Appendix C: Assessing the transport impacts of development proposals

1.1 It is necessary to carry out a proper assessment of the impact a development will have on highways and transportation to establish if it can be satisfactorily integrated into the existing infrastructure network. PPG13 also makes clear that the assessment of new development proposals should include their accessibility by a range of transport methods and developers are required to demonstrate how they will reduce travel to the site by car. So a thorough, properly-prepared transport assessment (TA) is often essential to support a development proposal.

1.2 This guidance is based on the Department for Communities and Local Government and the Department for Transport document ‘Guidance on Transport Assessments’ (GTA). You should read it with Part 2 of this document. Among other things, Part 2 gives guidance on the level of assessment - transport statement or transport assessment – that will normally be required for a range of different development types.

1.3 The general purpose of these guidelines is to set out clearly to you and your consultants what issues you may need to cover in either a transport statement or transport assessment. They are intended to help you prepare assessments that will allow us and the planning authority to properly understand and consider your development proposals. The aim should always be to reach agreement on transport issues before you submit any planning application; this reflects the emphasis placed in the GTA on the value of early pre-application discussions including both the highway and planning authorities. This should then avoid abortive work (work that doesn't produce the intended result) and unnecessary delays in determining any planning application.

1.4 Despite this guidance, it is difficult to impose rigid rules on the scope and content of a transport assessment, as this will depend on the circumstances which exist at each development site. You should always hold early discussions with us to agree site-specific requirements.

1.5 When you prepare a transport assessment (whatever the level), you consider the following:

You should consider these matters at an early stage in preparing a development proposal. The work you do on developing the transport assessment can then be used as a basis for discussions about the location of the site and the scale and mix of uses proposed.

1.6 We are currently preparing our own travel plan guidelines, but this appendix includes some general interim guidance.

1.7 The purpose of this section is to explain the general requirements for the different types of transport assessment and for scoping reports.  As part of the pre-application discussions, you should agree with us the type of assessment required before you start to prepare it. Please refer to Section TAG5 for more detailed guidance on assessment criteria and Section TAG6 for general guidance on travel plans.

1.8 A Transport statement (TS) should set out the transport issues relating to a proposed development site (existing conditions) and details of the development proposals (proposed development). Table PDP1 gives a general indication of the types and scales of development where a TS will normally be required.

1.9 A TS should be based on a sound analysis of existing conditions. You should provide a full description of:

This information should be accurately established to show how the development proposal fits in to existing conditions. The description should include at least the following:

1.10 A TS should clearly demonstrate how you are going to provide safe and satisfactory access to the development for pedestrians, cyclists (and if appropriate) public transport. As well as the site access junction, it should also consider any barriers to walking, cycling or using public transport in the immediate vicinity of the site access. Barriers can include:

The TS should contain a full description of the proposed development including the following.

1.11 The above is not a complete list of requirements. In certain circumstances it may be necessary to expand the scale and scope of a TS, for example:

You won’t necessarily have to consider all the above matters for a proposed development that requires a TS. So, you should always discuss and agree with us the requirements for your site before you begin to prepare a TS.

1.12 We will not normally require a draft travel plan as part of a TS. As indicated in Part 2, Table PDP1, we will normally only require a concept proposal as standard to support a TS for a residential development, and then normally only for one with more than 25 dwellings. Where we do require a concept proposal, it should fit together, clearly, consistently and logically with the TS, with any assumptions in one reflected in the other. For example, it will not be acceptable for the TS to state that occupiers will make a large number of cycle trips without the concept proposal demonstrating how you will provide good, safe, cycle access and facilities in practice.

1.13 You should always discuss and agree the site requirements with us before you begin to prepare a TS.

1.14 A transport assessment (TA) will normally be required for larger developments likely to have impacts over a wide area. Table PDP1 in Part 2 of this document gives a general indication of some of the types and scales of development.

1.15 A TA is more comprehensive than a transport statement (TS). Figure TAG1, which is based on extracts from the GTA sets out the general steps which you could typically need to follow when preparing an assessment and the basic components in the process of producing one.

Note: This Figure is based on GTA Figure Fig 4.1 and Fig 4.2. The Guidance on Transport Assessments is copyright of the Department for Transport and Department for Communities and Local Government.

You should discuss the site requirements with us as soon as possible. A TA should normally deal with the following issues:

- Reducing the need to travel, especially by car. Make sure from the beginning that you think about:

       to promote multipurpose or linked trips.

- Sustainable accessibility. You should:

- Dealing with residual trips. You should:

- Mitigation measures. Make sure as far as possible that the proposed measures to reduce the impact of the development promote innovative and sustainable transport solutions.

1.16 A draft travel plan should normally form part of a TA. As indicated in Part 2, Table PDP1, residential developments requiring a TA will normally also require a concept proposal. For retail, general employment, office, warehousing and other types of development requiring a TA, you should discuss and agree the need for a concept proposal with us.

1.17 The TA, draft travel plan and any concept proposal should fit together clearly, consistently and logically, with any assumptions in one reflected in the others. For example, it will not be acceptable for the TA to state that occupiers will make a large number of cycle trips without the concept proposal demonstrating how you will provide good, safe, cycle access and facilities in practice.  And, the draft travel plan should set out supporting measures and incentives to encourage cycling.

1.18 You should normally first prepare and agree a scoping report with us to determine the TA requirements for your site.

1.19 PPS13 states that you should hold early discussions with us to clarify whether we are likely to accept your proposals in principle in transport terms and to ‘scope’ (identify) the requirements for any transport assessment.  The Government’s ‘Guidance on Transport Assessments’ (GTA) also highlights that wherever pre-application consultation (discussion before an application is submitted) identifies a need for a TA, it is good practice to agree, as part of the pre-application consultation, to prepare a scoping report before you begin the TA.

1.20 You will normally need to prepare a scoping report (SR) before you prepare a TA. The purpose of the SR is to establish key factors that will influence later stages of work. These include an assessment of highway capacity, safety implications and the nature of improvements and measures which might be required to off-set the proposed developments impacts on the surrounding highways and transportation infrastructure. Establishing these key factors should avoid the possibility of you carrying out abortive work, based on incorrect assumptions, at the later stages. You should discuss and agree the SR with us before you prepare the TA and it should normally cover the following.

Depending on the nature of the development, you may need to provide a breakdown of vehicle type.

1.21 Based on the Government’s guidelines (GTA) a TA should normally include at least the following:

1.22 This may not be a complete list for your particular development. You should discuss site specific requirements with us at the earliest opportunity and agree the necessary details when you submit your scoping report.

1.23 Based on the Government’s guidelines (GTA) a TA should normally include at least:

1.24 This may not be a complete list for your particular development. You should discuss site specific requirements with us at the earliest opportunity and agree the necessary details when you submit the scoping report.

1.25 The purpose of this section is to detail assessment criteria.

1.26 The criteria below set down our normal requirements for the various aspects of assessing traffic impacts. You should discuss and agree details about specific sites with us before you prepare any scoping report or any type of transport assessment.

1.27 The site junction: This includes new junctions on to the highway network and existing junctions either in their current form or in an improved form. In all cases, junctions should normally be assessed at least:

1.28 The surrounding network: Existing junctions and links within any assessment area should normally be assessed in line with paragraph 1.27.

1.29 Proposed highway improvements: Where any improvements are required they should normally be assessed in line with paragraph 1.27.

1.30 We will require counts for peak-hour turning movements at existing junctions. In certain circumstances, for example, where the number of HGVs is an important consideration, we may need these counts classified. We may need other counts, for example:

in certain circumstances depending on the scale, nature and location of the development.

1.31 The scoping report and transport assessment should justify that the base traffic data reasonably reflects the normal, general current circumstances on the road network serving the site, and is valid for assessment purposes.

1.32 Assessments should normally include at least committed development traffic. Committed development will normally include development plan allocations and other development sites with a current planning consent.

1.33 It may also be appropriate to allow for general traffic growth. This will be assessed on a site-by-site basis, and will depend mainly on the constraints on the surrounding road network.

1.34 Where you need to project forward existing traffic flows, you should normally use either the National Road Traffic Forecasts (NRTF) or TEMPRO. In certain circumstances, however, we may have survey data that would enable you to establish a growth rate local to the site.

1.35 If a development site has or had an existing use, it may be appropriate to offset the likely traffic impacts of the proposed development against the site’s existing traffic impacts when considering its redevelopment.

1.36 If this is acceptable to us in principle, you will need to quantify the traffic impacts of any existing uses for the assessment periods. Where an existing use is still in full operation, you should normally establish its traffic impacts by up-to-date traffic counts at the site accesses.

1.37 For existing uses not in full operation, it may still be appropriate to carry out traffic surveys and then agree with us how much the increase in traffic is likely to be if the site is redeveloped (but see paragraph 1.38).

1.38 We will consider each site separately, particularly where the existing land uses no longer operates.  We will, where appropriate, take into account the validity of increasing the site’s operation or bringing the existing buildings back into operation without needing planning permission.

1.39 You should first work out the total trips – that is by all modes of transport (including walking) – that you expect the proposed development to generate. You can usually do this using TRICS*, or other data such as a traffic survey, where the new development is an expansion of an existing similar use, or a survey of a similar development in the same area. Where you use TRICS or other databases, the sites you choose should be appropriate and relevant to the proposed development, and the transport assessment should clearly demonstrate this. Whichever data source you use, you should include details of the sites used to form the basis of the predicted trip generation in the assessment.

*Note: Where TRICS or other appropriate databases do not contain enough information on similar sites, you will normally have to base the trip estimate on a detailed analysis of the proposed daily operation of the development.

1.40 85^th %ile trip generation rates should normally be used as a starting point, as the GTA recommends, but see also paragraph 1.42.

1.41 For retail developments, you should normally split trips by vehicles in to different types such as:

You should agree with us the percentage of each type of trip as part of the scoping report

1.42 Sometimes, it is suggested that the level of predicted vehicle trips can be reduced to reflect proposed improvements to public transport and walking and cycling facilities (‘sustainable transport’). We will normally only consider a reduction where:

1.43 For any committed developments, you should use data from the transport assessment prepared for that development where it is available. Otherwise, you should establish traffic generation as described in paragraph 1.39.

1.44 Depending on the scale, nature and location of the development appropriate methods might include:

1.45 You need to explain your methodology for distributing and assigning trips to the network.  If you have used a traffic model, you should set out the basis for the model assignment and include the following information:

1.46 If you have developed a manual gravity model, you should explain the formulae you have used and the assumptions you have built into the model.

1.47 If any committed developments are to be included in a transport assessment, where possible you should use available data from the assessment prepared for that development. Otherwise, traffic should be distributed in an appropriate method to be agreed with us.

1.48 The normal area should generally include all junctions where the increase in any traffic turning movement is:

1.49 Even where the overall traffic impact may be relatively small, you may still need to expand the area of assessment beyond the above to cover other parts of the road network, for example:

Note: In the following ‘base traffic’ means:

1.50 The highway capacity analysis should normally include at least:

1.51 The site access should normally be of a standard that will safely and satisfactorily accommodate whichever situation in paragraph 1.50 gives the worst traffic impact . Where further highway works are required on the network serving the development, they should normally be to a standard that ensures traffic conditions are no worse at any time during the period than if the development had not taken place.

1.52 There may be circumstances where the improvements needed to meet the normal requirement might not be appropriate. Examples might include:

1.53 We may be prepared to consider accepting a lower standard of improvement in such circumstances. We may, for example, accept a solution that, during the year that the development opens, leaves conditions no worse than if the development had not taken place. However, we will apply a graduated approach to accepting any lower-standard solution, similar to the approach of our highway access policy. Also, we will only accept a solution in a location where highway safety is not affected. We will seek to resist developments, for example by recommending refusal of any planning applications, where they would result in congestion that causes safety and environmental problems.

1.54 Any type of transport assessment should normally include an analysis of the previous five years’ accidents. We hold accident data which we will provide to you for a fee. As well as a summary of accident types and numbers, the assessment should also normally include a comparison of accident rates with national casualty rates and, where available, local county rates. It should also include reference to any identified ‘cluster’ sites.

1.55 In addition to the current situation, the transport assessment should also take into account our casualty-reduction targets. By 2010, we aim to:

compared to the average for 1994 - 98.

1.56 Where there are identified areas in the road network with safety problems, you should assess how any additional traffic may make existing problems worse.  You should include your findings in the transport assessment and propose possible measures to reduce the problems where appropriate. We will resist development proposals that could adversely affect road safety and threaten our casualty-reduction targets.

1.57 Where new junctions, improvements to existing junctions or other highway improvements are required as a result of the development, we will normally require road safety audits.

1.58 Where the nature, location and scale of a development proposal require a travel plan, a draft plan should form part of the transport assessment. You can find a general indication of some of the types and scales of development in table PDP1 in Part 2 of this guidance.

1.59 A travel plan is a package of measures or agreed outcomes aimed at reducing reliance on the private motor vehicle and reducing congestion. It is a process rather than a policy document. Indeed, completing the document itself is only the start of the process. A successful travel plan involves continuous monitoring (for example, surveys), review and improvement over time. So it does require a high level of debate about transport problems, options and future action, as well as a high-level management commitment. But where a plan is likely to deliver significant reductions in the use of private cars, this could reduce the scale of highway works required to off-set the development’s traffic impacts and could, in certain circumstances, result in the need for less off-street parking.

1.60 We are currently developing our own guidelines on preparing travel plans. In the meantime, before you prepare a transport assessment or scoping report, you should discuss likely draft plan requirements with us. Examples of likely broad issues to be considered and agreed include:

1.61 Where mitigating works and measures are required (to off-set the impact a development has on highways and transportation), these will normally be secured through planning conditions or appropriate legal agreement. The scale and nature of the works and measures will normally determine the appropriate approach.

1.62 Where improvements are required to the existing road network, these are normally carried out under a Section 278 agreement of the Highways Act. Please refer to Part 6 of this document.