1.26
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4139
Received: 30/08/2021
Respondent: Mr paul giles
The transport model used by AECOM is fundamentally flawed because the model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4161
Received: 30/08/2021
Respondent: Mrs MARGARET TURNER
The transport model used by AECOM is fundamentally flawed because the model has not been
validated/ calibrated (particularly with respect to public transport), the National Trip End Model
(NTEM) should not be used below district / county level, no uncertainty log has been prepared, it
doesn’t include household survey data, and the data has not been adequately tested. Strategic
models are not designed for use in a scheme specific assessment. The latter requires a revised
forecast model produced from a recalibrated base year model using additional and more recent data
with a more specific geographical focus of resources and modelling.
The transport model used by AECOM is fundamentally flawed because the model has not been
validated/ calibrated (particularly with respect to public transport), the National Trip End Model
(NTEM) should not be used below district / county level, no uncertainty log has been prepared, it
doesn’t include household survey data, and the data has not been adequately tested. Strategic
models are not designed for use in a scheme specific assessment. The latter requires a revised
forecast model produced from a recalibrated base year model using additional and more recent data
with a more specific geographical focus of resources and modelling.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4462
Received: 31/08/2021
Respondent: Mrs Lucy Crawford
The transport model used by AECOM is fundamentally flawed because the model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
"20 to 25 outbound car vehicle trips in the am peak hour"
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4538
Received: 01/09/2021
Respondent: Mrs Kathryn Smith
The transport model used by AECOM is fundamentally flawed. The model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model (NTEM) should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
The transport model used by AECOM is fundamentally flawed. The model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model (NTEM) should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4626
Received: 01/09/2021
Respondent: Mr Melvyn Chase
The transport model used by AECOM is fundamentally flawed because the model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
I have severe Parkinson’s and cannot type easily. Please duplicate all of Lucy Crawford’s responses for my views. Her email address is Lucy_crawford@hotmail.com and she lives at 33, Staploe PE19 5JA
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4629
Received: 01/09/2021
Respondent: Mr Melvyn Chase
The transport model used by AECOM is fundamentally flawed because the model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
I have severe Parkinson’s and cannot type easily. Please duplicate all of Lucy Crawford’s responses for my views. Her email address is Lucy_crawford@hotmail.com and she lives at 33, Staploe PE19 5JA
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4685
Received: 01/09/2021
Respondent: Mr Joshua Zwetsloot
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document. (para 2.4.3 of document inserted here).
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated.
In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4864
Received: 02/09/2021
Respondent: Ms Tara Skey
The transport model used by AECOM is fundamentally flawed because it has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model (NTEM) should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
The transport model used by AECOM is fundamentally flawed because it has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model (NTEM) should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4882
Received: 02/09/2021
Respondent: Mr Kevin Morrall
The brown development scenario shows Staploe Parish as urban. It is rural.
The brown development scenario shows Staploe Parish as urban. It is rural.
Support
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4972
Received: 02/09/2021
Respondent: Mr Chris Giles
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated.
In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 4992
Received: 02/09/2021
Respondent: Rainier Developments Limited (Bromham)
Agent: Marrons Planning
A Technical Note has been prepared by Jubb on behalf of Rainier Developments Limited, and is submitted by email separately.
A Technical Note has been prepared by Jubb on behalf of Rainier Developments Limited, and is submitted by email separately.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5002
Received: 02/09/2021
Respondent: Rainier Developments Limited (Roxton)
Agent: Marrons Planning
A Technical Note prepared by Jubb on behalf of Rainier Developments Limited is submitted by email separately.
A Technical Note prepared by Jubb on behalf of Rainier Developments Limited is submitted by email separately.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5014
Received: 02/09/2021
Respondent: Rainier Developments Limited (Roxton)
Agent: Marrons Planning
A Technical Note has been prepared by Jubb on behalf of Rainier Developments Limited and is submitted by email separately.
A Technical Note has been prepared by Jubb on behalf of Rainier Developments Limited and is submitted by email separately.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5015
Received: 02/09/2021
Respondent: Rainier Developments Limited (Wootton)
Agent: Marrons Planning
A Technical Note has been prepared by Jubb on behalf of Rainier Developments Limited and is submitted by email separately.
A Technical Note has been prepared by Jubb on behalf of Rainier Developments Limited and is submitted by email separately.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5176
Received: 03/09/2021
Respondent: Mr Ian Francis
Development north of Bedford has been ruled out because of the capacity constraints on the A6. However, the traffic
studies conducted already show that the capacity on the A6 will be exceeded when you include the existing
development planned for Local Plan 2030. Since then Bedford Borough Council have specified that the new East
West rail station must be in Bedford town centre so the issues on the A6 need to be resolved even without further
development north of Bedford. Twinwoods site can therefore not be defavoured on the grounds of inadequate capacity of the A6.
Development north of Bedford has been ruled out because of the capacity constraints on the A6. However, the traffic
studies conducted already show that the capacity on the A6 will be exceeded when you include the existing
development planned for Local Plan 2030. Since then Bedford Borough Council have specified that the new East
West rail station must be in Bedford town centre so the issues on the A6 need to be resolved even without further
development north of Bedford. Twinwoods site can therefore not be defavoured on the grounds of inadequate capacity of the A6.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5582
Received: 06/09/2021
Respondent: Mrs Julie Kilby
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5632
Received: 07/09/2021
Respondent: Mr Phillip Yockney
The transport model used by AECOM is fundamentally flawed because the model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model (NTEM) should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5684
Received: 07/09/2021
Respondent: Miss amber scally
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5736
Received: 07/09/2021
Respondent: Miss Hannah Hambleton-Jewell
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5770
Received: 07/09/2021
Respondent: Mrs Gillian Tagg
• The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
• No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
• It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
• TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
• For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
• Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
• These types of checks have not been undertaken to validate / calibrate the model.
• AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
• It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document. (extract inserted here)
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
100-word summary
The transport model used by AECOM is fundamentally flawed because the model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model (NTEM) should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5844
Received: 08/09/2021
Respondent: Mr Norman Hoy
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document. (Extract of document inserted here).
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
100 word summary
The transport model used by AECOM is fundamentally flawed because the model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model (NTEM) should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 5964
Received: 08/09/2021
Respondent: Staploe Parish Council
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document. [Extract inserted here.]
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node. Also Dennybrook will definitely by very heavy car reliant due to location and lack of transport links.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
100 word summary
The transport model used by AECOM is fundamentally flawed because the model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model (NTEM) should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 6005
Received: 08/09/2021
Respondent: Mrs Christina Farmer
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 6099
Received: 09/09/2021
Respondent: Jen Giles
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated.
In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 6203
Received: 09/09/2021
Respondent: Peter Coles
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 6304
Received: 10/09/2021
Respondent: Mr Paul Zwetsloot
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
pg. 11 of 25
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated.
pg. 12 of 25
In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 6426
Received: 13/09/2021
Respondent: Ms Donna Thompson
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
[PARAGRAPH 2.4.3 OF NEW SETTLEMENT WEST OF WYBOSTON DOCUMENT]
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 6432
Received: 13/09/2021
Respondent: Mr Steven Kent
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
pg. 15 of 23
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 6531
Received: 13/09/2021
Respondent: Mrs Susan Trolley
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document.
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
Object
Local Plan 2040 Draft Plan - Strategy options and draft policies consultation
Representation ID: 6590
Received: 14/09/2021
Respondent: Mr Aiden Farmer
The Transport Modelling undertaken by AECOM in support of the strategic options in the Draft Local Plan 2040 is fundamentally flawed for the following reasons.
No validation or calibration of the traffic model has been undertaken which is not in keeping with Department for Transport WebTAG guidance.
It is assumed that the Bedford Borough Transport Model was undertaken using Saturn, which was the model of choice for the Bedford Town Centre modelling project in 2015. In this case, Saturn cannot directly Model Public Transport therefore it is assumed that the engineers have made some significant assumptions with respect to public transport and trips being used, which have not been validated or calibrated.
TAG unit M1.2 introduces the National Trip End Model (NTEM). It includes forecasts of population, households, workforce and jobs over 30 years which are used in a series of models that forecast population, employment, car ownership, trip ends and traffic growth by Middle Layer Super Output Area (MSOA). The NTEM data set can be viewed using the TEMPro (Trip End Model Presentation Program) software. TEMPro estimates of trip ends at any level below aggregate regions (e.g. MSOA, district, or county level) are subject to uncertainty and should not be used as constraints in matrix development process without verification and possible adjustments. No uncertainty log was prepared which is a recommendation of WebTAG modelling guidance.
For direct use in matrix development, trip rate information estimated from household survey data should be considered instead to underpin trip end estimates at zone level. There is a risk that model may not be realistic or sensible due to the error around the model parameters used, or limitations in the extent to which the model can represent human behaviour. Therefore, before using any mathematical model, it is essential to check that it produces credible outputs consistent with observed behaviour. This is usually done by running the model for the base year (either the current year or a recent year), and:
• comparing its outputs with independent data (validation);
• checking that its response to changes in inputs is realistic, based on results from independent evidence (realism testing); and
• checking that the model responds appropriately to all its main inputs (sensitivity testing).
Five types of data can be collected and used to inform most models:
• data on the transport network, including the physical layout, number of lanes, signal timings, public transport frequencies and capacities;
• counts of vehicles or persons on transport services, links or at junctions;
• journey times;
• queue lengths at busy junctions;
• interview surveys, in which transport users are asked to describe trips either through household travel diaries or intercept surveys (e.g. roadside interviews, public transport onboard interview surveys.
These types of checks have not been undertaken to validate / calibrate the model.
AECOM have derived trip ends using CTripEnds for a number of journey purposes. Expanding synthetic trip ends produced by CTripEnd to the local zoning system is considered to be subject to significant discrepancies from observed especially if validation and the calibration exercise has not been undertaken.
It is also important to note that strategic models are not designed for use in a scheme specific assessment. For such an assessment it is recommended a revised forecast model would be produced from a recalibrated base year model using additional and more recent data and targeted to reflect a more specific geographical focus of resources and modelling effort.
As part of the Bedford Borough Transport Model documents it is quoted that average departing trips are 20 to 25 vehicles, which may be below the trip rates assumed as part of a detailed development assessment. The extract below is taken from the New Settlement West of Wyboston document. [Para 2.4.3 extract inserted.]
It is unknown what scenario of Dennybrook (site 977) development that the above “20 to 25 outbound car vehicle trips in the AM peak hour” relate to, however an outbound TRCS residential trip rate is somewhere between 0.23 to 0.33 vehicles per dwelling.
The development scenario ranges from 2,500 dwellings to 10,150 dwellings. On this basis and using a 0.25 departure trip rate results in 625 to 2,538 departing trips all of which would be home based departure trips. The model assumes 5 loading zones which therefore means there could be 125 to 508 vehicles per loading zone. This is significantly higher than the 20 to 25 outbound vehicle used by the AECOM model, assuming they have loaded it per node.
AECOM may claim that some of the departing trips will be internal and therefore will not cross cordon line however taking the 125 departing vehicle trips associated with 2,500 dwellings scenario; 20% of these departing vehicles are considered not to be leaving the area. This percentage decreases further if the worst case number of dwellings is being considered, i.e. 10,150 dwellings. It has previously been highlighted that the AECOM model has not be validated / calibrated and now given the apparent significant under valuation of the likely vehicle trips that will be generated, it is clear that the assessment of the capacity of junctions and the highway network is fundamentally flawed.
The significant undervaluation of generated vehicle trips could be argued by AECOM as being a reduction due to the impact of the public transport. However, the proposed new railway stations associated with the East West Rail Link are located to the east of the A1, which is significantly far enough away for the Dennybook development to be considered to not directly serve it without requiring a vehicle car trip to be generated. In this scenario it more likely that occupiers of Dennybrook (site 977) dwellings will continue their journey by car as opposed to transferring onto rail.
Given this all of the assessments undertaken by AECOM to determine the rerouting and vehicle km travelled for any scenario are highly unlikely to be representative.
Town planning principles are that new development should be centred on and around existing sustainable urban area where local infrastructure exists and allow residents to travel using public transport to serve the development which can be easily extended.
If larger new settlements are the only realistic option then they should be centred on transport hubs such as a new railway station so that they become the heart of the community and the de facto mode of travel. Locating a new settlement on the edge of town / out of town where the transport hub is also not well connected leads to a disjointed sustainable public transport which will always be second best to car travel.
1.26 100 word summary
The transport model used by AECOM is fundamentally flawed because the model has not been validated / calibrated (particularly with respect to public transport), the National Trip End Model (NTEM) should not be used below district / county level, no uncertainty log has been prepared, it doesn’t include household survey data, and the data has not been adequately tested. Strategic models are not designed for use in a scheme specific assessment. The latter requires a revised forecast model produced from a recalibrated base year model using additional and more recent data with a more specific geographical focus of resources and modelling.