I hearby reitterate the view on my parish council, and employed planning consultant on this matter..
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.

pg. 11 of 31
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 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.
For this reason we believe that if a new settlement is required the preferred option should be Little Barford as it will be
very close to the new East West Rail station and within walking distance of the current mainline station at St Neots.
However, our second preferred option would be Twinwoods where we believe a parkway station and mitigations for
the A6 can be provided towards the end of the plan period. Much of the site is brownfield land, there are no flooding
issues and it does not engulf a local existing settlement.