Planning for Sustainable Travel

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Settlement size refers to the total population or number of dwellings within a contiguous built-up area. Larger settlements provide an opportunity for greater self-containment and a mix of uses offering access to a range of shops, services and employment within the built-up area, thereby reducing the need for inter-urban travel. We should aim to maximise the proportion of new development which is allocated within or immediately adjacent to larger towns and cities.

Settlement Size

Key Questions

1. What is the ideal settlement size for sustainable travel?

There are many factors that are associated with sustainable travel and they tend to be inter-related, but data trends, using National Travel Survey (NTS) analysis, show that metropolitan areas and large urban areas and (at a minimum) settlements with a population of 25,000 tend to have shorter annual travel distances and lower car mode shares than average.

2. How much can larger settlements help reduce travel by car?

There is broadly an inverse linear relationship with increased average distance travelled as settlement size decreases:

More data trends are here.

Settlement size is very closely related to factors such as density, mix of use and accessibility. These factors, and others such as socio-economic and attitudinal characteristics, also have a strong influence on travel. In the larger urban areas, a number of centres can be developed, reflecting the concepts of ‘polycentricity’ or ‘decentralised concentration’, where suburban centres are developed as local town centres, complementing the ‘compact’ high order main urban centre.

Selective Policy Guidance ShowHide

“At a regional level the Regional Spatial Strategy should identify broad locations for new housing so that the need and demand for housing can be addressed in a way that reflects sustainable development principles…taking into account:

  • the contribution to be made to cutting carbon emissions from focusing new development in locations with good public transport accessibility and/or by means other than the private car
  • options for accommodating new housing growth (or renewal of existing housing stock) taking into account opportunities for, and constraints on, development. Options may include, for example, the re-use of vacant or derelict sites, additional housing in established residential areas, large scale redevelopment and redesign of existing areas, expansion of existing settlements through urban extensions and creation of new freestanding settlements.” (PPS3, para 37)

‘‘Where need and demand are high it will be necessary to identify and explore a range of options for distributing housing, including the role of the growth area, growth points, new freestanding settlements, major urban extensions and the managed growth of settlements in urban and rural areas and/or where necessary review any policy constraints.” (PPS3, para 37)

More here

Planning Checklist: Settlement Size

The following issues should be considered while planning at the regional and sub-regional level.

1.1. Consider the advantages of locating development in selected larger urban areas (metropolitan areas, cities and large towns, or above 25,000 population at a minimum), to (a) reduce the need to travel, and (b) support public transport provision, by:

  • increasing the likelihood of residents finding jobs and utilising facilities, or of services drawing their employees and customers, from within the same urban area
  • tending to have higher development density
  • creating higher volumes of traffic demand on the main corridors
  • [higher densities and better public transport] requiring and facilitating a managed approach to car parking which itself contributes to lower car ownership and use

It may not always be practicable or desirable to maximise development in or adjacent to the largest urban areas within any region/sub-region because of the local incidence of housing need, support for smaller, rural communities and their services, restricted land availability and/or environmental or infrastructure constraints. However, expansion of larger settlements is generally preferable to ‘leapfrogging’ development to smaller towns or ‘spreading’ development across a number of settlements:

1.2. Where applicable, development should not be dispersed across and replicating the existing settlement pattern. Strategic traffic generation impacts should contribute to locational considerations. This may involve a review of Green Belt and similar urban containment policies (from the perspective of sustainable transport) where the expansion of settlements may have been prevented. Consider the option of selective release of land at the edge of larger settlements and in public transport corridors taking into account:

  • the relative accessibility by public transport of alternative locations to jobs and major facilities
  • the likely difference in per capita car mileage
  • the potential to ‘swap’ other locations for open space provision

Evidence and Examples

The evidence given here is necessarily selective, but gives an introduction to the research on this topic. More details are found in the background technical report.

Ecotec (1993) and Banister et al (1997) provided early analyses of the UK National Travel Survey (NTS) dataset, finding that there are relationships between settlement size (and other variables) and travel. The Ecotec work in particular established a base of understanding about land use and transport relationships in the UK and fed into the development of the 1994 version of PPG13.

WSP and Arup (2005) also note that travel distance decreases with increased settlement size. Their analysis suggests that there are advantages in locating residential development in urban areas with a minimum of 25,000 population.

Research on settlement size and energy efficiency of travel in South Oxfordshire paints a complex picture. The most energy efficient settlement included in the study was one of the largest towns (Henley), where there was a high trip generation rate (i.e. total number of trips) but low energy consumption rate per person and trip, reflecting a good provision of local facilities and services. The least energy efficient settlement was a small, remote settlement (Ewelme) with limited services and facilities. The settlement was too small to be self-sufficient and travel by car was essential to reach work and facilities. Towns in the intermediate settlement sizes produced a confused picture where population structure, distance from employment and other facilities, and levels of car ownership were all important factors in determining the energy efficiency of travel [strongly correlated with carbon emissions] (Banister, 1980; Banister, 1992). This research demonstrates the importance of settlement size and accessibility to other urban areas and other factors in determining travel patterns.

Various models of urban structure can help us to conceptualise differences in travel behaviour across settlements of similar size. ‘Polycentricity’ and ‘deconcentrated concentration’ both involve growth concentrated at multiple locations, or town centres, as found in larger urban areas such as Greater London or some of the larger metropolitan areas. This structure may reduce trip distances by providing local facilities (Owens, 1992; Breheny and Rookwood, 1993). Hall and Ward (1998), Hall and Pain (2006) also encourage development clusters along public transport infrastructure, including [re-opened] railway lines, in the UK. This linear development pattern uses the strategic [public] transport network as its structural spine.

Further reading here

Summary Guide Summary Guide Background Technical Report Background Technical Report Sherford, Plymouth

Sherford, Plymouth - Devon County and South Hams District Council have chosen to meet “rural” housing demand by an urban extension to Plymouth, at Sherford, rather than (an) isolated development(s) in the countryside.
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Didcot, Oxfordshire - Historic Green Belt policy in Oxford has led to residential development being diverted to the country towns surrounding Oxford. This has led to some concerns, from the sustainable transport perspective, in light of the negative impacts of long-distance commuting and other concerns. The recent South East Plan proposes a review of the Green Belt and a major urban extension to the south east of Oxford.
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Northstowe, South Cambridgeshire - Northstowe (Cambridge) is a new community that will provide 9,500 dwellings for up to 24,000 people as well as shops, services and employment centres.
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