Transport assessments for planning

Many developers in England hear early on that their scheme needs a transport assessment or a transport statement.

These notes explain what each one is and how the traffic side is put together. They follow the government's planning guidance and the National Planning Policy Framework.

Assessment or statement

A transport assessment is a thorough study of how a development will affect travel around it. A transport statement is a lighter version. It suits a scheme whose transport effects are expected to be limited.

The planning framework asks for one or the other where a development is likely to generate significant amounts of movement. It also asks for a travel plan, which sets out how walking, cycling and public transport will be encouraged over time. Where the effects are not significant, none of these may be needed.

Agreeing the scope early

The government's guidance says the need, scale and level of detail should be settled as early as possible. The council, the developer and the relevant transport authorities should agree what is needed for each scheme.

Early agreement helps in a practical way. It can shape the design of the development while changes are still easy to make. Local plans may also set their own thresholds for what counts as a significant amount of movement.

What goes into one

The guidance lists the topics a transport assessment or statement should consider when its scope is settled. They include these.

The site layout and how people will get in and out by every mode of transport.
Current public transport services and how often they run.
Current traffic flows on nearby roads and junctions, and which ones matter most.
Injury accident records near the site access for the latest three years, or five in a high accident area.
Trips from other committed development nearby that is likely to go ahead within three years.
Parking, and measures to reduce the need to travel.

Where traffic modelling comes in

An assessment needs a view of traffic in the future, not only today. The guidance says forecasts should normally use local traffic projections such as TEMPro. TEMPro is free software from the Department for Transport that shows trip forecasts by area, mode, time of day and purpose.

The study usually looks at normal conditions, such as a school-term weekday. It may also look at regular peaks such as rush hours. The current framework asks for reasonable future scenarios, including cumulative effects and trips by every mode. It also asks the study to start from a vision of what the development is trying to achieve.

Motorways and major A roads

National Highways runs the strategic road network in England, which is the motorways and major trunk A roads. It is a statutory consultee in the planning system.

It offers a pre-application service and invites early contact where a scheme may affect safety or queuing on its roads. It aims to answer most enquiries within 21 days. Its policy asks that assumptions behind traffic forecasts are stated clearly, and that the scenarios tested are agreed with it.

How a decision is reached

The framework says significant adverse effects on capacity, congestion or highway safety should be mitigated to an acceptable degree. A proposal should be refused only where its effect on the network would be severe, or its effect on highway safety unacceptable, after taking mitigation into account. That test covers the construction phase as well as the finished scheme.

In Wales, the national guidance on transport and planning is Technical Advice Note 18.