Transport Assessment

A Transport Assessment is a comprehensive and systematic process that sets out transport issues relating to a proposed development. It identifies what measures will be taken to deal with the anticipated transport impacts of the scheme and to improve accessibility and safety for all modes of travel, particularly for alternatives to the car such as walking, cycling and public transport.

In some cases, the transport issues arising out of a development proposal may not require a full Transport Assessment to inform the process adequately and identify suitable mitigation. In these instances, it has become common practice to produce a simplified report in the form of a Transport Statement. There will also be situations where the transport issues relating to a development proposal are limited, and no formal assessment is necessary.

Transport Assessments should consider the impact of the development on all transport modes, set out proposals to minimise the impact of the development on the transport network and promote measures to encourage sustainable transport. To this end, it is a usual requirement that a Transport Assessment is accompanied by a Travel Plan that will be implemented as part of the development proposals upon occupation and sets out measures to encourage sustainable transport.

The Transport Assessment process and the development of measures to encourage sustainable travel should be developed through consultation with the relevant authorities. This is an iterative process that often requires a number of revisions to the development proposals and sustainable travel measures before it can be agreed that the transport impact of the development has been reduced to a minimum. At this point the residual transport impact is assessed and mitigation measures are designed as necessary. The diagram below outlines the normal approach:-

Recommended Approach to a Transport Assessment

This iterative approach to the Transport Assessment ensures that improvements to sustainable modes of transport are always considered first, with measures to increase the capacity of roads or junctions only considered at the end of the process to mitigate the residual traffic impact of the development.

Transport Assessments identify the impact of the development in ‘person trips’, which are then broken down by transport mode. This normally involves the use of the nationally accepted TRICS database that enables the calculation of person/vehicle trips rates for different forms of development. Alternatively the use of bespoke survey data from other development sites are used, which can give a more accurate estimate of trip generation if a suitably representative site can be found in close proximity to the development site being considered.

Once development trips have been estimated, the distribution of trips can be predicted though various techniques, including gravity models or using existing travel pattern information or other empirical data. Information is also gathered on any existing person/vehicle trips from the existing use of the site and these are discounted from the network, to produce a net increase or decrease in trips within agreed assessment periods, which are usually considered during weekday AM/PM and weekend peak hour periods.

Once the net trip predictions are known, the local transport network is examined to establish whether capacity exists that can adequately accommodate development trips. When assessing the traffic impact on the highway network, this usually requires assessment of the immediate highway links and junction connections, with the scope of assessment limited to the highway network where the potential for material impact is anticipated. The traffic assessment will potentially include junction modelling of traffic movements in existing, opening and future design year scenarios, which are normally at least 5 years hence. Surveys of existing traffic flows on the local network are required to establish the base situation, with traffic growth factors applied to predict future design year conditions, derived through the National Trip End Model (NTEM) forecasts or other empirical data.

Where the traffic assessment identifies that the level of additional traffic movements cannot be accommodated by existing infrastructure, then off site highway improvements need to be considered to ensure that the impact of the development is neutral, i.e. that it is no worse than existing circumstances. Similarly pedestrian/cycle routes and public transport facilities are examined and if improvements are necessary to accommodate development trips, then improvements need to be considered to these facilities to encourage access by sustainable modes.

The operational safety of a development is a key consideration and a detailed appraisal of the recorded personal injury accident records for the local highway network is usually required, determining casualty, linked factors and common problems that may need to be addressed as part of the development.

The assessment concludes with a summary of its findings and recommendations outlining the developments compliance with the National Planning Policy Framework (NPPF 2018) and other Governmental Departmental Guidance.

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Transport Assessment, Anticipated Transport Impacts, Transport Statement, Transport Network Sustainable Transport, Travel Plan, Department For Transport, Person Trips, National Planning Policy, NPPFTRICS, Gravity Models, Local Transport Network, National Trip End Model