1.23

Object

Representation ID: 8358

Received: 03/09/2021

Respondent: Mrs K Francis

BBC have concluded that Twinwoods creates such a traffic problem at the Clapham Road/Manton Lane junction in Bedford that it is not a suitable development site as the developer has not proposed a solution to the congestion at that junction. Staploe Parish Council believe that conclusion is incorrect.
• The transport model starts with the 2018 base year model previously developed and then adds to that the growth identified by Bedford Borough Council in the adopted local plan to 2030 and includes the mitigations (traffic schemes) that are planned to happen by 2030. This then creates the reference case at year 2030, against which the different development scenarios to 2040 and to 2050 are compared.
• One of the measures of the impact the developments will have on the highway network, is the Junction-Volume Capacity Ratio. This shows how congested the junctions will be – so a figure of 100% means that the junction is fully utilised, i.e. congested, leading to delays at that junction.
• Tables 3.15 (for 2040) and 3.16 (for 2050, but incorrectly titled for 2040) show the Junction-Volume Capacity Ratios for the PM peak Hour in 2040 and 2050 for the unmitigated and mitigated Twinwoods scenarios. The 4 lines for the Clapham Road/Manton Lane junction as follows:
see table 3.15 and 3.15 of AECOM report




• You will see that the black boxes denote 100% or more Ratio – i.e. the junction is completely full (on 3 of the 4 legs) and congested.
• The report at paras 3.5.21 and 3.5.22 states:
• 3.5.21 Table 3.9 to Table 3.16 highlight that there is forecast to be significant delays and congestion issues at the Clapham Road / Manton Lane Junction, particularly in the PM Peak hour. These forecast delays and high volume-capacity ratios are present within the 2030 reference case, with volume-capacity ratios forecast to be above 100% on three out of the four arms at this junction. These high forecast volume capacity ratios are maintained or are forecast to worsen in the 2040 and 2050 forecasts including the proposed Twinwoods and / or Colworth developments.
• 3.5.22 As part of the forecasting assumptions for the reference case (see Table 2.2), an improvement scheme at this location, which provides a dedicated left-turn lane for Clapham Road southbound traffic to Manton Lane and the part-signalisation of the roundabout, is included. Further mitigation at this location was considered as part of this study to alleviate the forecast congestion, but due to the constraints at this location (such as existing buildings and Bedford Modern School) no further mitigation has been proposed as part of this study.
• The junction is already completely full at 2030 before any new developments or the addition of an east west rail statoin. Therefore this is a Bedford Borough Council problem that will already happen due to the growth in the adopted Local plan 2030. Bedford Borough Council will have to solve this – not the developers of Twinwoods.
• It should be noted that when Twinwoods is included the Junction-Volume Capacity Ratios increase (on 3 of the 4 legs) from 100% to between 101% and 105% which is negligible in the overall scale of the issue.
• Para 4.2.9 concludes :
• 4.2.9 Significant forecast delays and capacity constraints are forecast at the Clapham Road / Manton Lane roundabout in northern Bedford, primarily in the PM Peak hour, both in the reference case and with the inclusion of the proposed developments and mitigation measures. The reference case includes improvements to this junction; however, further mitigation at this junction to alleviate the forecast congestion has not been proposed as part of this study due to the physical constraints at this location. Without further capacity improvements or measures to reduce the forecast traffic at this location, the forecast congestion at this junction is likely to be a constraint on the delivery of growth along the A6 corridor to the north of the borough.
• This demonstrates that this is not a new development issue, but an existing issue that Bedford Borough Council will have to solve before 2030 – particularly in view of the fact that all traffic wanting to access the new East West Rail Station from the north of the Borough will need to use the A6 to reach the station in central Bedford.
• 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.

Object

Representation ID: 8428

Received: 03/09/2021

Respondent: Mr Theodore Cassell

BBC have concluded that Twinwoods creates such a traffic problem at the Clapham Road/Manton Lane junction in Bedford that it is not a suitable development site as the developer has not proposed a solution to the congestion at that junction. I believe that conclusion is incorrect.
• The transport model starts with the 2018 base year model previously developed and then adds to that the growth identified by Bedford Borough Council in the adopted local plan to 2030 and includes the mitigations (traffic schemes) that are planned to happen by 2030. This then creates the reference case at year 2030, against which the different development scenarios to 2040 and to 2050 are compared.
• One of the measures of the impact the developments will have on the highway network, is the Junction-Volume Capacity Ratio. This shows how congested the junctions will be – so a figure of 100% means that the junction is fully utilised, i.e. congested, leading to delays at that junction.
• Tables 3.15 (for 2040) and 3.16 (for 2050, but incorrectly titled for 2040) show the Junction-Volume Capacity Ratios for the PM peak Hour in 2040 and 2050 for the unmitigated and mitigated Twinwoods scenarios. The 4 lines for the Clapham Road/Manton Lane junction as follows:
see Table 3.15 and table 3.16 of AECOM report
You will see that the black boxes denote 100% or more Ratio – i.e. the junction is completely full (on 3 of the 4 legs) and congested.
• The report at paras 3.5.21 and 3.5.22 states:
• 3.5.21 Table 3.9 to Table 3.16 highlight that there is forecast to be significant delays and congestion issues at the Clapham Road / Manton Lane Junction, particularly in the PM Peak hour. These forecast delays and high volume-capacity ratios are present within the 2030 reference case, with volume-capacity ratios forecast to be above 100% on three out of the four arms at this junction. These high forecast volume capacity ratios are maintained or are forecast to worsen in the 2040 and 2050 forecasts including the proposed Twinwoods and / or Colworth developments.
• 3.5.22 As part of the forecasting assumptions for the reference case (see Table 2.2), an improvement scheme at this location, which provides a dedicated left-turn lane for Clapham Road southbound traffic to Manton Lane and the part-signalisation of the roundabout, is included. Further mitigation at this location was considered as part of this study to alleviate the forecast congestion, but due to the constraints at this location (such as existing buildings and Bedford Modern School) no further mitigation has been proposed as part of this study.
• The junction is already completely full at 2030 before any new developments or the addition of an east west rail station in Bedford Town Centre. Therefore this is a Bedford Borough Council problem that will already happen due to the growth in the adopted Local plan 2030 (1500 new homes all north of Bedford which will impact the A6 by 2030). Bedford Borough Council will have to solve this – not the developers of Twinwoods but a development at Twinwoods might contribute some infrastructure funding to help mitigate the problems on the A6
• It should be noted that when Twinwoods is included the Junction-Volume Capacity Ratios increase (on 3 of the 4 legs) from 100% to between 101% and 105% which is negligible in the overall scale of the issue.
• Para 4.2.9 concludes :
• 4.2.9 Significant forecast delays and capacity constraints are forecast at the Clapham Road / Manton Lane roundabout in northern Bedford, primarily in the PM Peak hour, both in the reference case and with the inclusion of the proposed developments and mitigation measures. The reference case includes improvements to this junction; however, further mitigation at this junction to alleviate the forecast congestion has not been proposed as part of this study due to the physical constraints at this location. Without further capacity improvements or measures to reduce the forecast traffic at this location, the forecast congestion at this junction is likely to be a constraint on the delivery of growth along the A6 corridor to the north of the borough.
• This demonstrates that this is not a new development issue, but an existing issue that Bedford Borough Council will have to solve before 2030 – particularly in view of the fact that all traffic wanting to access the new East West Rail Station from the north of the Borough will need to use the A6 to reach the station in central Bedford.


• 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.

1.23 100 word summary

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. Therefore infrastructure funds from a new development could contribute to this.

In addition the AECOM transport modelling is fundamentally flawed.

Object

Representation ID: 8533

Received: 03/09/2021

Respondent: Mrs Claire francis

BC have concluded that Twinwoods creates such a traffic problem at the Clapham Road/Manton Lane junction in Bedford that it is not a suitable development site as the developer has not proposed a solution to the congestion at that junction. I believe that conclusion is incorrect.
• The transport model starts with the 2018 base year model previously developed and then adds to that the growth identified by Bedford Borough Council in the adopted local plan to 2030 and includes the mitigations (traffic schemes) that are planned to happen by 2030. This then creates the reference case at year 2030, against which the different development scenarios to 2040 and to 2050 are compared.
• One of the measures of the impact the developments will have on the highway network, is the Junction-Volume Capacity Ratio. This shows how congested the junctions will be – so a figure of 100% means that the junction is fully utilised, i.e. congested, leading to delays at that junction.
• Tables 3.15 (for 2040) and 3.16 (for 2050, but incorrectly titled for 2040) show the Junction-Volume Capacity Ratios for the PM peak Hour in 2040 and 2050 for the unmitigated and mitigated Twinwoods scenarios. The 4 lines for the Clapham Road/Manton Lane junction as follows:
See Table 3.15 and 3.16 of AECOM report
• You will see that the black boxes denote 100% or more Ratio – i.e. the junction is completely full (on 3 of the 4 legs) and congested.
• The report at paras 3.5.21 and 3.5.22 states:
• 3.5.21 Table 3.9 to Table 3.16 highlight that there is forecast to be significant delays and congestion issues at the Clapham Road / Manton Lane Junction, particularly in the PM Peak hour. These forecast delays and high volume-capacity ratios are present within the 2030 reference case, with volume-capacity ratios forecast to be above 100% on three out of the four arms at this junction. These high forecast volume capacity ratios are maintained or are forecast to worsen in the 2040 and 2050 forecasts including the proposed Twinwoods and / or Colworth developments.
• 3.5.22 As part of the forecasting assumptions for the reference case (see Table 2.2), an improvement scheme at this location, which provides a dedicated left-turn lane for Clapham Road southbound traffic to Manton Lane and the part-signalisation of the roundabout, is included. Further mitigation at this location was considered as part of this study to alleviate the forecast congestion, but due to the constraints at this location (such as existing buildings and Bedford Modern School) no further mitigation has been proposed as part of this study.
• The junction is already completely full at 2030 before any new developments or the addition of an east west rail station in Bedford Town Centre. Therefore this is a Bedford Borough Council problem that will already happen due to the growth in the adopted Local plan 2030 (1500 new homes all north of Bedford which will impact the A6 by 2030). Bedford Borough Council will have to solve this – not the developers of Twinwoods but a development at Twinwoods might contribute some infrastructure funding to help mitigate the problems on the A6
• It should be noted that when Twinwoods is included the Junction-Volume Capacity Ratios increase (on 3 of the 4 legs) from 100% to between 101% and 105% which is negligible in the overall scale of the issue.
• Para 4.2.9 concludes :
• 4.2.9 Significant forecast delays and capacity constraints are forecast at the Clapham Road / Manton Lane roundabout in northern Bedford, primarily in the PM Peak hour, both in the reference case and with the inclusion of the proposed developments and mitigation measures. The reference case includes improvements to this junction; however, further mitigation at this junction to alleviate the forecast congestion has not been proposed as part of this study due to the physical constraints at this location. Without further capacity improvements or measures to reduce the forecast traffic at this location, the forecast congestion at this junction is likely to be a constraint on the delivery of growth along the A6 corridor to the north of the borough.
• This demonstrates that this is not a new development issue, but an existing issue that Bedford Borough Council will have to solve before 2030 – particularly in view of the fact that all traffic wanting to access the new East West Rail Station from the north of the Borough will need to use the A6 to reach the station in central Bedford.


• 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.

Object

Representation ID: 8605

Received: 13/09/2021

Respondent: Mr Henry Zwetsloot

BBC have concluded that Twinwoods creates such a traffic problem at the Clapham Road/Manton Lane junction in Bedford that it is not a suitable development site as the developer has not proposed a solution to the congestion at that junction. Staploe Parish Council believe that conclusion is incorrect.
• The transport model starts with the 2018 base year model previously developed and then adds to that the growth identified by Bedford Borough Council in the adopted local plan to 2030 and includes the mitigations (traffic schemes) that are planned to happen by 2030. This then creates the reference case at year 2030, against which the different development scenarios to 2040 and to 2050 are compared.
• One of the measures of the impact the developments will have on the highway network, is the Junction-Volume Capacity Ratio. This shows how congested the junctions will be – so a figure of 100% means that the junction is fully utilised, i.e. congested, leading to delays at that junction.
• Tables 3.15 (for 2040) and 3.16 (for 2050, but incorrectly titled for 2040) show the Junction-Volume Capacity Ratios for the PM peak Hour in 2040 and 2050 for the unmitigated and mitigated Twinwoods scenarios. The 4 lines for the Clapham Road/Manton Lane junction as follows:
[TABLE 3.15 AND TABLE 3.16 from evidence base document]
• You will see that the black boxes denote 100% or more Ratio – i.e. the junction is completely full (on 3 of the 4 legs) and congested.
• The report at paras 3.5.21 and 3.5.22 states:
• 3.5.21 Table 3.9 to Table 3.16 highlight that there is forecast to be significant delays and congestion issues at the Clapham Road / Manton Lane Junction, particularly in the PM Peak hour. These forecast delays and high volume-capacity ratios are present within the 2030 reference case, with volume-capacity ratios forecast to be above 100% on three out of the four arms at this junction. These high forecast volume capacity ratios are maintained or are forecast to worsen in the 2040 and 2050 forecasts including the proposed Twinwoods and / or Colworth developments.
• 3.5.22 As part of the forecasting assumptions for the reference case (see Table 2.2), an improvement scheme at this location, which provides a dedicated left-turn lane for Clapham Road southbound traffic to Manton Lane and the part-signalisation of the roundabout, is included. Further mitigation at this location was considered as part of this study to alleviate the forecast congestion, but due to the constraints at this location (such as existing buildings and Bedford Modern School) no further mitigation has been proposed as part of this study.
• The junction is already completely full at 2030 before any new developments or the addition of an east west rail station in Bedford Town Centre. Therefore this is a Bedford Borough Council problem that will already happen due to the growth in the adopted Local plan 2030 (1500 new homes all north of Bedford which will impact the A6 by 2030). Bedford Borough Council will have to solve this – not the developers of Twinwoods but a development at Twinwoods might contribute some infrastructure funding to help mitigate the problems on the A6
• It should be noted that when Twinwoods is included the Junction-Volume Capacity Ratios increase (on 3 of the 4 legs) from 100% to between 101% and 105% which is negligible in the overall scale of the issue.
• Para 4.2.9 concludes :
• 4.2.9 Significant forecast delays and capacity constraints are forecast at the Clapham Road / Manton Lane roundabout in northern Bedford, primarily in the PM Peak hour, both in the reference case and with the inclusion of the proposed developments and mitigation measures. The reference case includes improvements to this junction; however, further mitigation at this junction to alleviate the forecast congestion has not been proposed as part of this study due to the physical constraints at this location. Without further capacity improvements or measures to reduce the forecast traffic at this location, the forecast congestion at this junction is likely to be a constraint on the delivery of growth along the A6 corridor to the north of the borough.
• This demonstrates that this is not a new development issue, but an existing issue that Bedford Borough Council will have to solve before 2030 – particularly in view of the fact that all traffic wanting to access the new East West Rail Station from the north of the Borough will need to use the A6 to reach the station in central Bedford.


• 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.

Object

Representation ID: 8672

Received: 13/09/2021

Respondent: Mr J Francis

BBC have concluded that Twinwoods creates such a traffic problem at the Clapham Road/Manton Lane junction in Bedford that it is not a suitable development site as the developer has not proposed a solution to the congestion at that junction. Staploe Parish Council believe that conclusion is incorrect.
• The transport model starts with the 2018 base year model previously developed and then adds to that the growth identified by Bedford Borough Council in the adopted local plan to 2030 and includes the mitigations (traffic schemes) that are planned to happen by 2030. This then creates the reference case at year 2030, against which the different development scenarios to 2040 and to 2050 are compared.
• One of the measures of the impact the developments will have on the highway network, is the Junction-Volume Capacity Ratio. This shows how congested the junctions will be – so a figure of 100% means that the junction is fully utilised, i.e. congested, leading to delays at that junction.
• Tables 3.15 (for 2040) and 3.16 (for 2050, but incorrectly titled for 2040) show the Junction-Volume Capacity Ratios for the PM peak Hour in 2040 and 2050 for the unmitigated and mitigated Twinwoods scenarios. The 4 lines for the Clapham Road/Manton Lane junction as follows:
[TABLE 3.15 AND TABLE 3.16 from evidence base document]
• You will see that the black boxes denote 100% or more Ratio – i.e. the junction is completely full (on 3 of the 4 legs) and congested.
• The report at paras 3.5.21 and 3.5.22 states:
• 3.5.21 Table 3.9 to Table 3.16 highlight that there is forecast to be significant delays and congestion issues at the Clapham Road / Manton Lane Junction, particularly in the PM Peak hour. These forecast delays and high volume-capacity ratios are present within the 2030 reference case, with volume-capacity ratios forecast to be above 100% on three out of the four arms at this junction. These high forecast volume capacity ratios are maintained or are forecast to worsen in the 2040 and 2050 forecasts including the proposed Twinwoods and / or Colworth developments.
• 3.5.22 As part of the forecasting assumptions for the reference case (see Table 2.2), an improvement scheme at this location, which provides a dedicated left-turn lane for Clapham Road southbound traffic to Manton Lane and the part-signalisation of the roundabout, is included. Further mitigation at this location was considered as part of this study to alleviate the forecast congestion, but due to the constraints at this location (such as existing buildings and Bedford Modern School) no further mitigation has been proposed as part of this study.
• The junction is already completely full at 2030 before any new developments or the addition of an east west station. Therefore this is a Bedford Borough Council problem that will already happen due to the growth in the adopted Local plan 2030. Bedford Borough Council will have to solve this – not the developers of Twinwoods
• It should be noted that when Twinwoods is included the Junction-Volume Capacity Ratios increase (on 3 of the 4 legs) from 100% to between 101% and 105% which is negligible in the overall scale of the issue.
• Para 4.2.9 concludes :
• 4.2.9 Significant forecast delays and capacity constraints are forecast at the Clapham Road / Manton Lane roundabout in northern Bedford, primarily in the PM Peak hour, both in the reference case and with the inclusion of the proposed developments and mitigation measures. The reference case includes improvements to this junction; however, further mitigation at this junction to alleviate the forecast congestion has not been proposed as part of this study due to the physical constraints at this location. Without further capacity improvements or measures to reduce the forecast traffic at this location, the forecast congestion at this junction is likely to be a constraint on the delivery of growth along the A6 corridor to the north of the borough.
• This demonstrates that this is not a new development issue, but an existing issue that Bedford Borough Council will have to solve before 2030 – particularly in view of the fact that all traffic wanting to access the new East West Rail Station from the north of the Borough will need to use the A6 to reach the station in central Bedford.


• 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.

Object

Representation ID: 8735

Received: 28/09/2021

Respondent: Mrs Nicola Gooch

1.23 Bedford Borough Transport Model New Settlements and the A6 – AECOM
BBC have concluded that Twinwoods creates such a traffic problem at the Clapham Road/Manton Lane junction in Bedford that it is not a suitable development site as the developer has not proposed a solution to the congestion at that junction. I believe that conclusion is incorrect.
• The transport model starts with the 2018 base year model previously developed and then adds to that the growth identified by Bedford Borough Council in the adopted local plan to 2030 and includes the mitigations (traffic schemes) that are planned to happen by 2030. This then creates the reference case at year 2030, against which the different development scenarios to 2040 and to 2050 are compared.
• One of the measures of the impact the developments will have on the highway network, is the Junction-Volume Capacity Ratio. This shows how congested the junctions will be – so a figure of 100% means that the junction is fully utilised, i.e. congested, leading to delays at that junction.
• Tables 3.15 (for 2040) and 3.16 (for 2050, but incorrectly titled for 2040) show the Junction-Volume Capacity Ratios for the PM peak Hour in 2040 and 2050 for the unmitigated and mitigated Twinwoods scenarios. The 4 lines for the Clapham Road/Manton Lane junction as follows:
• See table 3.15

• See table 3.16

• You will see that the black boxes denote 100% or more Ratio – i.e. the junction is completely full (on 3 of the 4 legs) and congested.
• The report at paras 3.5.21 and 3.5.22 states:
• 3.5.21 Table 3.9 to Table 3.16 highlight that there is forecast to be significant delays and congestion issues at the Clapham Road / Manton Lane Junction, particularly in the PM Peak hour. These forecast delays and high volume-capacity ratios are present within the 2030 reference case, with volume-capacity ratios forecast to be above 100% on three out of the four arms at this junction. These high forecast volume capacity ratios are maintained or are forecast to worsen in the 2040 and 2050 forecasts including the proposed Twinwoods and / or Colworth developments.
• 3.5.22 As part of the forecasting assumptions for the reference case (see Table 2.2), an improvement scheme at this location, which provides a dedicated left-turn lane for Clapham Road southbound traffic to Manton Lane and the part-signalisation of the roundabout, is included. Further mitigation at this location was considered as part of this study to alleviate the forecast congestion, but due to the constraints at this location (such as existing buildings and Bedford Modern School) no further mitigation has been proposed as part of this study.
• The junction is already completely full at 2030 before any new developments or the addition of an east west rail station in Bedford Town Centre. Therefore this is a Bedford Borough Council problem that will already happen due to the growth in the adopted Local plan 2030 (1500 new homes all north of Bedford which will impact the A6 by 2030). Bedford Borough Council will have to solve this – not the developers of Twinwoods but a development at Twinwoods might contribute some infrastructure funding to help mitigate the problems on the A6
• It should be noted that when Twinwoods is included the Junction-Volume Capacity Ratios increase (on 3 of the 4 legs) from 100% to between 101% and 105% which is negligible in the overall scale of the issue.
• Para 4.2.9 concludes :
• 4.2.9 Significant forecast delays and capacity constraints are forecast at the Clapham Road / Manton Lane roundabout in northern Bedford, primarily in the PM Peak hour, both in the reference case and with the inclusion of the proposed developments and mitigation measures. The reference case includes improvements to this junction; however, further mitigation at this junction to alleviate the forecast congestion has not been proposed as part of this study due to the physical constraints at this location. Without further capacity improvements or measures to reduce the forecast traffic at this location, the forecast congestion at this junction is likely to be a constraint on the delivery of growth along the A6 corridor to the north of the borough.
• This demonstrates that this is not a new development issue, but an existing issue that Bedford Borough Council will have to solve before 2030 – particularly in view of the fact that all traffic wanting to access the new East West Rail Station from the north of the Borough will need to use the A6 to reach the station in central Bedford.


• 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.

1.23 100 word summary

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. Therefore infrastructure funds from a new development could contribute to this.

In addition the AECOM transport modelling is fundamentally flawed.

Object

Representation ID: 8764

Received: 29/09/2021

Respondent: Staploe Parish Council

BBC have concluded that Twinwoods creates such a traffic problem at the Clapham Road/Manton Lane junction in Bedford that it is not a suitable development site as the developer has not proposed a solution to the congestion at that junction. Staploe Parish Council believe that conclusion is incorrect.
• The transport model starts with the 2018 base year model previously developed and then adds to that the growth identified by Bedford Borough Council in the adopted local plan to 2030 and includes the mitigations (traffic schemes) that are planned to happen by 2030. This then creates the reference case at year 2030, against which the different development scenarios to 2040 and to 2050 are compared.
• One of the measures of the impact the developments will have on the highway network, is the Junction-Volume Capacity Ratio. This shows how congested the junctions will be – so a figure of 100% means that the junction is fully utilised, i.e. congested, leading to delays at that junction.
• Tables 3.15 (for 2040) and 3.16 (for 2050, but incorrectly titled for 2040) show the Junction-Volume Capacity Ratios for the PM peak Hour in 2040 and 2050 for the unmitigated and mitigated Twinwoods scenarios. The 4 lines for the Clapham Road/Manton Lane junction as follows:
SEE TABLES 3.15 AND 3.16 OF BEDFORD BOROUGH TRANSPORT MODEL NEW SETTLEMENTS AND THE A6

• You will see that the black boxes denote 100% or more Ratio – i.e. the junction is completely full (on 3 of the 4 legs) and congested.
• The report at paras 3.5.21 and 3.5.22 states:
• 3.5.21 Table 3.9 to Table 3.16 highlight that there is forecast to be significant delays and congestion issues at the Clapham Road / Manton Lane Junction, particularly in the PM Peak hour. These forecast delays and high volume-capacity ratios are present within the 2030 reference case, with volume-capacity ratios forecast to be above 100% on three out of the four arms at this junction. These high forecast volume capacity ratios are maintained or are forecast to worsen in the 2040 and 2050 forecasts including the proposed Twinwoods and / or Colworth developments.
• 3.5.22 As part of the forecasting assumptions for the reference case (see Table 2.2), an improvement scheme at this location, which provides a dedicated left-turn lane for Clapham Road southbound traffic to Manton Lane and the part-signalisation of the roundabout, is included. Further mitigation at this location was considered as part of this study to alleviate the forecast congestion, but due to the constraints at this location (such as existing buildings and Bedford Modern School) no further mitigation has been proposed as part of this study.
• The junction is already completely full at 2030 before any new developments or the addition of an east west rail station in Bedford Town Centre. Therefore this is a Bedford Borough Council problem that will already happen due to the growth in the adopted Local plan 2030 (1500 new homes all north of Bedford which will impact the A6 by 2030). Bedford Borough Council will have to solve this – not the developers of Twinwoods but a development at Twinwoods might contribute some infrastructure funding to help mitigate the problems on the A6
• It should be noted that when Twinwoods is included the Junction-Volume Capacity Ratios increase (on 3 of the 4 legs) from 100% to between 101% and 105% which is negligible in the overall scale of the issue.
• Para 4.2.9 concludes :
• 4.2.9 Significant forecast delays and capacity constraints are forecast at the Clapham Road / Manton Lane roundabout in northern Bedford, primarily in the PM Peak hour, both in the reference case and with the inclusion of the proposed developments and mitigation measures. The reference case includes improvements to this junction; however, further mitigation at this junction to alleviate the forecast congestion has not been proposed as part of this study due to the physical constraints at this location. Without further capacity improvements or measures to reduce the forecast traffic at this location, the forecast congestion at this junction is likely to be a constraint on the delivery of growth along the A6 corridor to the north of the borough.
• This demonstrates that this is not a new development issue, but an existing issue that Bedford Borough Council will have to solve before 2030 – particularly in view of the fact that all traffic wanting to access the new East West Rail Station from the north of the Borough will need to use the A6 to reach the station in central Bedford.


• 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.

1.23 100 word summary

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. Therefore infrastructure funds from a new development could contribute to this.

In addition the AECOM transport modelling is fundamentally flawed.

Object

Representation ID: 8885

Received: 30/09/2021

Respondent: Mr Peter Mills

BBC have concluded that Twinwoods creates such a traffic problem at the Clapham Road/Manton Lane junction in Bedford that it is not a suitable development site as the developer has not proposed a solution to the congestion at that junction. I believe that conclusion may be incorrect.
• The transport model starts with the 2018 base year model previously developed and then adds to that the growth identified by Bedford Borough Council in the adopted local plan to 2030 and includes the mitigations (traffic schemes) that are planned to happen by 2030. This then creates the reference case at year 2030, against which the different development scenarios to 2040 and to 2050 are compared.
• One of the measures of the impact the developments will have on the highway network, is the Junction-Volume Capacity Ratio. This shows how congested the junctions will be – so a figure of 100% means that the junction is fully utilised, i.e. congested, leading to delays at that junction.
1.23 100 word summary
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. Therefore infrastructure funds from a new development could contribute to this.

Object

Representation ID: 8925

Received: 01/10/2021

Respondent: Mr James Browning

BBC have concluded that Twinwoods creates such a traffic problem at the Clapham Road/Manton Lane junction in Bedford that it is not a suitable development site as the developer has not proposed a solution to the congestion at that junction. I believe that conclusion is incorrect.
• The transport model starts with the 2018 base year model previously developed and then adds to that the growth identified by Bedford Borough Council in the adopted local plan to 2030 and includes the mitigations (traffic schemes) that are planned to happen by 2030. This then creates the reference case at year 2030, against which the different development scenarios to 2040 and to 2050 are compared.
• One of the measures of the impact the developments will have on the highway network, is the Junction-Volume Capacity Ratio. This shows how congested the junctions will be – so a figure of 100% means that the junction is fully utilised, i.e. congested, leading to delays at that junction.
• Tables 3.15 (for 2040) and 3.16 (for 2050, but incorrectly titled for 2040) show the Junction-Volume Capacity Ratios for the PM peak Hour in 2040 and 2050 for the unmitigated and mitigated Twinwoods scenarios. The 4 lines for the Clapham Road/Manton Lane junction as follows:
•

•

• You will see that the black boxes denote 100% or more Ratio – i.e. the junction is completely full (on 3 of the 4 legs) and congested.
• The report at paras 3.5.21 and 3.5.22 states:
• 3.5.21 Table 3.9 to Table 3.16 highlight that there is forecast to be significant delays and congestion issues at the Clapham Road / Manton Lane Junction, particularly in the PM Peak hour. These forecast delays and high volume-capacity ratios are present within the 2030 reference case, with volume-capacity ratios forecast to be above 100% on three out of the four arms at this junction. These high forecast volume capacity ratios are maintained or are forecast to worsen in the 2040 and 2050 forecasts including the proposed Twinwoods and / or Colworth developments.
• 3.5.22 As part of the forecasting assumptions for the reference case (see Table 2.2), an improvement scheme at this location, which provides a dedicated left-turn lane for Clapham Road southbound traffic to Manton Lane and the part-signalisation of the roundabout, is included. Further mitigation at this location was considered as part of this study to alleviate the forecast congestion, but due to the constraints at this location (such as existing buildings and Bedford Modern School) no further mitigation has been proposed as part of this study.
• The junction is already completely full at 2030 before any new developments or the addition of an east west rail station in Bedford Town Centre. Therefore this is a Bedford Borough Council problem that will already happen due to the growth in the adopted Local plan 2030 (1500 new homes all north of Bedford which will impact the A6 by 2030). Bedford Borough Council will have to solve this – not the developers of Twinwoods but a development at Twinwoods might contribute some infrastructure funding to help mitigate the problems on the A6
• It should be noted that when Twinwoods is included the Junction-Volume Capacity Ratios increase (on 3 of the 4 legs) from 100% to between 101% and 105% which is negligible in the overall scale of the issue.
• Para 4.2.9 concludes :
• 4.2.9 Significant forecast delays and capacity constraints are forecast at the Clapham Road / Manton Lane roundabout in northern Bedford, primarily in the PM Peak hour, both in the reference case and with the inclusion of the proposed developments and mitigation measures. The reference case includes improvements to this junction; however, further mitigation at this junction to alleviate the forecast congestion has not been proposed as part of this study due to the physical constraints at this location. Without further capacity improvements or measures to reduce the forecast traffic at this location, the forecast congestion at this junction is likely to be a constraint on the delivery of growth along the A6 corridor to the north of the borough.
• This demonstrates that this is not a new development issue, but an existing issue that Bedford Borough Council will have to solve before 2030 – particularly in view of the fact that all traffic wanting to access the new East West Rail Station from the north of the Borough will need to use the A6 to reach the station in central Bedford.


• 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.

Object

Representation ID: 8994

Received: 01/10/2021

Respondent: Bedfordia Developments Ltd and Marcol Industrial Investments LLP

Agent: Lichfields

Comments on transport modelling evidence– for full assessment see attachment (appendix 1)
64. The transport modelling evidence presented thus far is incomplete and, in its current form, is not a sufficient level of evidence upon which to base planning based decisions. It fails to identify a number of critical elements which will undoubtedly influence the decision making process.
65. It fails to acknowledge the limitations of the modelling software in terms of how it is calibrated, how simplistic mode shift and sustainable transport is considered, that the time periods are restricted to single hours and that it is based on an assumption that current travel movements will be reinforced by traffic growth.
66. There is a significant lack of consideration being given to sustainable and active modes within the development of a mitigation strategy.
67. There is a failure to distinguish between development specific impacts and those which occur as a result of the application of an additional 10 years of traffic growth.
68. The inclusion of 10 years ‘generic’ growth is, in itself, questionable as it makes it difficult to discern development specific impacts and means that the mitigation strategy derived through the modelling is one which can only reinforce existing travel patterns and exacerbate car dependence.
69. The exacerbation results from continuing to seek to provide capacity for predicted traffic movements all of which are based on a set of assumptions around growth and trip generation which have not, themselves, been suitably tested. By not assessing the sensitivities of conclusions to certain modelling assumptions it cannot be determined how critical to the plan any of the measures identified may be.
70. There is a failure to consider the relationship between development strategy and mitigation. No regard has been given, within the isolated scenario tests, to understanding which developments are likely to rely on or contribute towards different mitigation measures. Consistent application of certain measures across all scenarios means it is not possible to determine if a development is dependent upon a measure (as a series of measures are included from the onset rather than those which are essential for a development to be delivered). Similarly, where Reference Case mitigation is not yet fully funded or permitted it should be identified as such to ensure that the reliance on mitigation of differing levels of certainty is fully identified within the assessment work.
71. The strategic model is not, in isolation, a suitable tool upon which judgements about junction capacity can be made but this is not made clear within the reporting. More refined modelling should be undertaken in areas where capacity has been identified as a constraining factor. This refined testing should consider an approach which better reflects capacity (ideally Microsimulation but, as a minimum Isolated junction modelling). It should also test how sensitive these conclusions are to other factors such as the omission of the generic TEMPRO growth and/or peak spreading and retiming of trips to allow judgements on whether mitigation is essential or desirable (i.e. if a modest change in demand negates the need for a scheme then it can, at best, only be determined as desirable).
72. Further testing should be cognisant of what it is reasonable and realistic to expect each development to deliver by way of mitigation, uniform inclusion of certain measures which are not yet permitted and/or lack funding for full delivery obfuscates the identification of development impacts, specifically when considering different development specific allocation strategies. More critically, this fails to recognise that each development brings with it unique benefits by way of mitigation strategies, especially if a foundation of mitigation is assumed in each option regardless of wether it can be delivered. Larger developments have the ability to deliver more mitigation without adversely impacts viability but this has not been considered in the modelling to date.