Object

Representation ID: 5984

Received: 08/09/2021

Respondent: Staploe Parish Council

Infrastructure items are already identified within the adopted Local Plan, principally at policy 90S. What is critical is the timing for delivery of necessary infrastructure to support the adopted Local Plan and draft Local Plan going forward. If there is a transport corridor approach to growth then additional junction improvements may be required, and priority bus routes that interconnect with existing and proposed rail stations, including the East West rail station to the south of St Neots. We also believe that it is important to improve the A6 to the north of Bedford to enable those in the north of the Borough to access the town centre and the new East West rail station.
I do not believe that the transport modelling was adequate. 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 centre on transport hubs such as a new railway stations 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.

If Little Barford is deemed unsuitable our second preferred option would be a new settlement of 2,500 homes at Twinwoods or Colworth. The Parish Council believe that the problems on the A6 north of Bedford are going to need to be resolved anyway in order to support the housing development proposed in the 2030 plan and for residents to access the east west rail station in the centre of the town. We believe that development of a new settlement of up to 3,000 homes at Twinwoods (site 883) or Colworth (site 1002) could provide the infrastructure funding to support improvements to the A6 which have long been needed and provide residents with access to the east west rail station in Bedford. A northern parkway station could be considered in future to provide sustainable transport for those in the north of the Borough. Twinwoods would include a significant proportion of brownfield land and Colworth includes lower quality (grade 3) agricultural land and so would comply with the NPPF requirement to utilise brownfield land or lower quality agricultural land before high quality agricultural land. These sites would also support Bedford Town Centre. Colworth was the site supported in the 2035 plan which was later reviewed. The A6 was not a considered sufficiently problematic to prevent this site being adopted so we find it hard to understand why the A6 is deemed such an insurmountable problem now.
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), a strategic model has been used incorrectly and the data has not been tested. AECOM have significantly undervalued the number of vehicle trips. Dennybrook is too far from the proposed new E-W rail station to cause such a significant reduction in car use. Therefore we believe that if a new settlement is required it should be at Little Barford. Our second choice would be Twinwoods with a guided busway or parkway station.