Research and analysis

Land use and transport planning: DfT Science Advisory Council paper

Published 29 April 2024

The Department for Transport (DfT) Science Advisory Council (SAC) convened on 2 October 2023 to provide an independent perspective on the opportunities for science and evidence to encourage land use and transport planning decision-making which supports policy outcomes as well as commercial imperatives. The session included input from additional government officials and external experts^{[footnote 1]}, but the content of this paper is the responsibility of the SAC alone.

Context

The spatial and modal patterns of demand for freight and passenger movements, both locally and nationally, are substantially influenced by locations and densities of land use, which are in turn affected by commercial and governmental decisions on planning and development. Land use and resulting patterns of demand have a strong influence on trip lengths and intensities and, in conjunction with transport network and service provision, on the modal shares of trips.

Hence, a wide range of transport-related policies with the following aims are directly or indirectly affected by land use planning:

• reducing greenhouse gas emissions
• delays and congestion
• air pollution
• road traffic accidents
• nuisance noise

Successful delivery of these transport policies matters – many aim to support a healthier society, which in turn is more economically active and prosperous.

In theory, academic and transport professionals have collectively recognised for over half a century the connections between land use and movement patterns, such as in the Ministry of Transport-commissioned report on traffic in towns in 1963. A growing body of empirical evidence has demonstrated this relationship. However, in practice, the use of this evidence to inform planning decisions has been inconsistent and rather limited, with non-transport factors playing a more major role.

This SAC meeting sought to evaluate the state of scientific and technical evidence that underpins land use and transport planning policies and the extent to which this is reflected in current implementation. Views were provided by consultants, planners and sustainable mobility agencies with extensive experience in the area.

Summary of expert views and discussion

Many larger housing developments can by many mobility measures be considered to be ‘in the wrong place’ from a transport perspective. They often are mainly accessible only by car and provide limited opportunities for using other modes of transport that may be lower in greenhouse gas emissions or support public health through active travel. They may not support an ageing population where accessibility of local facilities and public transport becomes important to personal independence and quality of life.

Developments often lack comprehensive internal pedestrian and cycle networks and may be poorly connected to high quality public transport services and regional cycle networks. The primary development goal is often to build houses, rather than to create communities with facilities close at hand. The post-war new towns adopted a more comprehensive community perspective and achieved higher proportions of internal commuting trips than comparable settlements developed in different eras. A broader, systems-thinking approach is now required, which starts with a comprehensive vision for a new development and then designs it to achieve the intended outcomes.

In general, there are few examples of new settlements in the UK that have been built fully on sustainability principles, including prioritising sustainable transport modes. There are however some international examples, such as Freiburg in Germany, where a major and sustained investment in public transport, walking and cycling has led to substantial reductions in car travel^{[footnote 2]}.

There is a need for better visibility of case studies showing what ‘good’ or ‘different’ looks like, with robust data on how design and planning subsequently influence travel patterns, lifestyles and more generally well-being.

This would be supported by designs based on a triple access planning^{[footnote 3] [footnote 4]} model, that supports sustainable mobility, access to residents’ needs within a short walk or cycle ride, and support digital connectivity for all. Planning and design of new settlements, and the creation of success metrics, will require a refocusing of objectives around maximising accessibility, rather than mobility. For example, transport patterns and community behaviour patterns may change if a food store and primary school are close by in a development.

DfT is developing a postcode-based connectivity tool for assessing/scoring the sustainability of a potential development site. This has the potential to provide a UK-wide self-consistent approach to considering the contextual accessibility of development and its potential for supporting different travel options. The tool, together with local planning policies, could be used to enhance the sustainability of developments by encouraging developers to increase sustainable transport infrastructure within and around low-scoring developments.

Alternatively, developments in high-scoring locations might be permitted to build at a higher density. Embedding the tool in the National Planning Policy Framework, with a requirement for a minimum connectivity score to gain planning approval, could lead to developments offering a wider range of travel options beyond the car.

Public transport services and facilities that can be provided locally on a commercial or semi-commercial basis depend heavily on the density of that development. Densities in the UK tend to be lower than in most European countries, at around 15 homes gross per hectare. Relatively little research has been undertaken into the effects of higher residential densities on the viability of local service provision, and how to design these developments in ways that meet people’s expectations for public space, privacy and so on.

Furthermore, where attempts have been made to provide good bus service or local facilities, these only become viable (and are introduced) after a substantial portion of the development has been occupied – by which time early residents have developed car-based living patterns that rely on reaching destinations away from the settlement. Looking forward, innovative services, such as on-demand or shared mobility need to be considered within the mix of local transport options available. Potentially long-lasting impacts on transport choices during transitionary phases of development are poorly evidenced at present.

For most new developments, local authority officers are required to produce a traffic impact assessment. This provides estimates of peak hour traffic generation from the site and its likely impact on the surrounding road network. For smaller schemes, these estimates are taken from databases – such as the trip rate information computer system (TRICS) – that use data from comparable existing developments.

However, as previously noted, there are very few examples and hence datasets of sustainable mobility developments on which to draw – so most data within these models relate to car-oriented developments. For larger developments, authorities generally rely on estimates provided by the national trip end model (NTEM). These estimates do not consider the influence of local connectivity on trip modal shares but rather use regional averages within which most developments are car-oriented. The decision-makers on local planning committees do not necessarily feel well enough informed to challenge these estimates provided by DfT.

The consequence is that most major housing developments require substantial road building and/or junction capacity increases to meet the anticipated increases in car trips and so be approved. These investments are generally hugely expensive (tens to hundreds of millions of pounds). If some fraction of that investment were directed towards high-quality active travel, public transport networks and local community facilities then levels of car use could be substantially reduced and the net community benefits could be much greater.

The limited number of examples of new housing developments have supported primarily investments in sustainable mobility rather than car-based access, and the poor monitoring and evaluation of these cases, have resulted in a shortage of evidence of its effectiveness. This represents a major evidence barrier to encouraging more sustainable developments.

Linked to this, there is a case for considering a wider range of factors and datasets when assessing the impacts of a proposed development, including its:

• walkability and the quality of the public realm
• transport equity
• physical, mental health and well-being
• local economic vitality
• social capital

Meeting net zero targets locally and nationally will require development and planning to place greater emphasis on likely carbon emissions and capital/embedded carbon. Promotion of meeting broader economic, health and well-being objectives is something that DfT and the Department for Levelling Up, Housing and Communities (DLUHC) could take a leadership role in promoting – successfully meeting these wider objectives is likely to affect the designs of developments that are approved. A major technical barrier is the lack of access to data on impacts and how they are affected by design considerations.

Recent research by consultants and academics, using a proposed development at Elton Reservoir in the Bury area as a case study, has shown the need to combine sustainable land use policies and innovative mobility solutions if transport carbon reduction targets are to be achieved^{[footnote 5]}.

The national planning policy framework sets out to encourage sustainable development through references to high-quality, walkable places and planning sustainable development into schemes. However, collective experiences indicated that the policy was frequently not being put into effective practice. The wording in the framework may not sufficiently empower local authorities to reject schemes that do not fit the framework without the risk of losing at appeal. For example, there must be an ‘unacceptable impact’ on highway safety, which is difficult to prove.

More generally, definitions of what is ‘sustainable’ are vague. Given multiple pressures, for example, to deliver additional housing alongside climate action, improved health and wider environmental gain (for example, in biodiversity, air quality and noise), there is an opportunity for this national framework to be reviewed.

The structures and processes for planning and approving developments are not comprehensive or consistent. Practitioners often report what is implemented by developers can differ significantly from what local planners originally had in mind. There are no clear lines of responsibility for decision-making, resulting often in a lack of consistency in the translation of policy into delivery. There are substantial risks of siloed working and lack of collaboration across the professions and organisations involved. When development proposals are subject to an examination in public, there can be limited consideration of transport issues.

At a practical level, local planning authorities can be limited in their access to the skills and expertise needed for ensuring successful cross-organisation/professional collaboration. Planning authorities are often not effective at negotiating with developers on issues, such as how sites should be laid out and what financial support should be provided to underwrite local services during the build-out phase.

More generally, meeting DfT goals may need a change in culture that better defines sustainability and better supports its delivery through re-framing and training for decision-makers, including the Planning Inspectorate.

Recommendations

Local highway and planning authorities are cautious about approving developments based on infrastructure that encourages movement patterns based on active travel and public transport, supported by high levels of digital connectivity. These developments would have correspondingly lower levels of residential car parking and network capacity for car movements within and to/from the site.

Local authorities’ presumption is generally in favour of replicating existing patterns of transport provision, ‘just in case’ occupants choose to drive everywhere – implicitly prioritising car use over other passenger modes.

Scientific and evidence recommendations include:

1. There is a need for more robust datasets collating evidence that shows the effects of building sustainable transport networks and local facility provision into new developments. These datasets need to include trip numbers, trip lengths and mode shares – plus wider health, social, economic and environmental indicators. Given the limited evidence available in the UK, data should be sought from international case studies. There is a need to build a wider evidence base of what ‘good’ looks like for a variety of contexts and scales, referenced to designs of new developments for car-independency that are shown to have been successful.

2. There is an opportunity to quantitatively evaluate how higher-density residential developments might play a role in supporting better quality public transport (including demand-responsive) services and a wider range of local community facilities. Evidence is needed to show how good planning and design can rise to the challenge of meeting residents’ needs (and allaying their concerns) and maximising the attractiveness of these developments.

3. The tools used to estimate the trip/traffic generation of new sites and larger developments (such as TRICS and NTEM) should be refined to reflect the connectivity and sustainable mobility provisions of a proposed development, and its likely impacts on travel patterns. This should be linked to the DfT connectivity tool and assessments made which take into account a much wider range of indicators, including a greater emphasis on carbon impacts. These analyses should be consolidated in a comprehensive transport impact assessment as part of the assessment of individual developments and local plans.

4. Further evaluation is needed of the current incentive structures that motivate the various actors to promote largely car-dependent developments and identify pricing or regulatory changes that would help align commercial interests with other objectives around public health, net zero and quality of life.

5. A study should be commissioned into the governance arrangements that underpin the land use planning process and its operation in practice, taking a broader systems view and accounting for the various private and public sector actors, at both local and national levels. The aim would be to identify barriers and conflicting pressures when trying to promote sustainable developments, including community facilities and sustainable transport networks.

6. The national planning policy framework should be reviewed to ensure it fully reflects the current science and evidence in support of delivering sustainable developments including recommending the DfT connectivity tool as a site-sifting mechanism; and ensuring that its wording empowers local authorities to reject schemes that do not fit the framework without the risk of losing at appeal.

7. Training using the latest data and evidence should be provided to enable important actors – in local and national government, the private sector and relevant agencies – to better address sustainability considerations and work collaboratively, along with the resources needed to support and promote sustainable developments that provide realistic travel choices.

Authors

• Professor Peter Jones, University College London (lead author)
• Professor William Powrie, University of Southampton (lead author)
• Professor Alastair Lewis (SAC Chair), University of York
• James Gaade, The Faraday Institution
• Anna-Marie Greenaway, University of Cambridge
• Dr Siddartha Khastgir,  WMG, University of Warwick
• Professor Ricardo Martinez-Botas, Imperial College London
• Professor Rob Miller, University of Cambridge
• Professor Nick Pidgeon, Cardiff University
• Dr Emma Taylor, Cranfield University
• Professor Patricia Thornley, Aston University

1. David Milner, Deputy Director of Create Street, Jon Sandford from Homes England, Lynda Addison, Chair of Transport Planning Society, Ben Plowden, PA Consulting and Chair of Transport Planning Society, Mike Axon, Global Director of Transport at SLR Consulting, Graham Grant from Active Travel England. ↩

2. Buehler and Pucher, Sustainable transport in Freiburg: lessons from Germany’s environmental capital. International Journal of Sustainable Transport, Vol 5, Issue 1. 2011. ↩

3. See Tap for uncertainty for more information. ↩

4. See Transport extra article for more information. ↩

5. See the Bridging the gap research study, (PDF) for more information. ↩