THEME 3 - STRATEGIC TRANSPORT NETWORK
The strategic transport network refers to transport infrastructure that supports medium and long-distance travel, generally between towns and cities or along major corridors in urban areas. It includes all modes whose configuration and design serves, and could potentially influence, spatial development patterns (e.g. rail, bus priority route and highway). The strategic network can be conceived as an integrated network of different modes and ownership – with combined conflicts and opportunities. For example, the solution to potential future congestion on the trunk road network may lie in the location of new development.
Built-up areas are not generally ‘self-sufficient’. To increase the sustainability of long-distance travel between settlements, the aim should be to:
- Increase the efficiency and reliability of the existing public transport network (rail and bus) and invest in public transport infrastructure improvements.
- Create development patterns that support public transport usage and discourage the use of the strategic highway network for short and medium distance travel. Major development should hence be located near to public transport nodes where capacity exists or can be developed.
1. Does locating development next to the strategic transport network lead to longer trips?
Research in Oxfordshire (M40) (Headicar, 1997, 2000) and Surrey (M25/M3/A3; rail commutes into London) (Hickman and Banister, 2007a) demonstrates the impact of locating development with easy access to the strategic route network – road and rail. Households increase travel distance on aggregate, and tend to favour the mode in question.
2. To what extent does expansion of the strategic transport network “induce” traffic demand?
This topic has been well researched, certainly in relation to highway capacity, indicating that induced traffic exists – the size of which varies according to context. Elasticities for capacity improvements range from 10% of the base traffic in the short run, and 20% in the long run (Goodwin et al, 2004; SACTRA, 1999). The induced travel effects of public transport expansion are less well understood. There are also reverse effects evident – road capacity reductions leading to a “degeneration” of traffic at the area-wide level (Cairns, Atkins, Goodwin, 2002). There likely to be contextual influences, including spatial location and form.
3. Do improvements to the strategic transport network lead to new land development?
Expansion of the highway network can lead to long term land use changes where land is available for development. Similarly, the availability of public transport infrastructure can facilitate new development or a higher intensity of development. See related themes on strategic development location and density.
“The [Highways] Agency cannot be expected to cater for unconstrained traffic generated by new development proposals. Such growth would be unsustainable and would restrict opportunities for future development where available capacity is limited. Development should be promoted at sustainable locations, and the Agency will expect to see demand management measures incorporated in development proposals.” Circular 2/07 (para 23)
“The likely availability and use of public transport is a very important ingredient in determining locational policies designed to reduce the need for travel by car.[…] The aim should be to establish a high quality, safe, secure and reliable network of routes, with good interchanges, which matches the pattern of traffic demand in order to maximise the potential usage of public transport.” PPG13 (para 72)
“Quick, easy and safe interchange is essential to integration between different modes of transport. Local authorities should promote more sustainable travel choices, by:
- ensuring that interchange points are well related to travel generating uses, and that the design, layout and access arrangements of surrounding development and interchanges are safe and convenient so as to maximise the walking and cycling catchment population for public transport services;
- identifying and, where appropriate, protecting sites and routes, both existing and potential, which could be critical in widening choices for passengers and ensuring that any such disused transport sites and routes are not unnecessarily severed by new development or transport infrastructure. In relation to rail use, this should be done in liaison with the SRA.” PPG13 (para 48)
Planning Checklist: Strategic Transport Network
Key issues to consider in regional and sub-regional planning are outlined below:
3.1. Develop sub-regional and city-regional governance structures (e.g. Multi-Area Agreements) that support an effective process for achieving integration in transport and urban planning.
3.2. Develop key public transport linkages and networks between cities and towns and within larger conurbations (in collaboration with national government) and locate development adjacent to nodes to make use of capacity.
3.3. Improve the efficiency of the strategic transport network by increasing integration between modes, for example at important urban and edge-of-town interchanges and park-and-ride sites.
3.4. Prioritise public transport infrastructure investments that support desired development patterns.
3.5. Make more efficient use of available road capacity through traffic demand management measures and road space reallocation to more sustainable modes.
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.
Analysis of travel behaviour in Oxfordshire has shown that new housing development located close to the strategic transport network increases travel distance and influences mode split (Headicar, 1996 and 2000). Similarly, research in Surrey shows that households located close to the strategic highway network are associated with high energy consumption patterns: the A31 (in particular), A3, M25 and M3 all contribute to lengthy commutes by car. Better access to the strategic road network in Surrey extends the distance that can be travelled in a fixed time (Hickman and Banister, 2007a).
Induced travel refers to shifts from other modes, longer trips and new trips resulting from improvements to the transport network. This is over and above trips that shift in time of day, route and/or destination as a result of network expansion (Goodwin et al, 2004; SACTRA, 1999; Litman 2009). A review of evidence on induced traffic demand from road network expansion shows that effects are greater over the long term, with short-term effects having an elasticity of 0 to 0.4 and long-term elasticities ranging from 0.5 to 1.0. This means a 10% increase in road capacity would cause up to a 4% increase in vehicle miles travelled (VMT) in the short term and up to a 10% increase in the long term (Schiffer et al, 2005).
The induced travel effects of public transport expansion are less well understood. The concept of stable travel budgets means that, overall, people tend to spend the same amount of time and money on travel relative to other activities no matter the options available to them (Schafer, 2008). Thus, a faster, more reliable or cheaper public transport network would encourage people to shift from other modes, to make longer trips or to make extra trips by public transport. However, the need to access public transport by another mode (e.g. walking and cycling) means that these types of adjustments may be more constrained by development patterns than similar behavioural changes that have been observed as the result of road capacity expansion.
The availability of public transport has an impact on modal share and trip rates. A study of the San Francisco Bay Area showed that pedestrian and bicycle modal shares and trip rates tended to be considerably higher, in some cases five time as high, in transit-oriented than in auto-oriented neighbourhoods with similar socio-economic characteristics. Transit neighbourhoods also averaged around 70 more daily transit work trips per 1,000 households than auto-oriented neighbourhoods, though trip rates varied considerably by socio-economic factors and other neighbourhood characteristics. Higher residential densities were also found to have a proportionately greater impact on transit commuting in transit-oriented than in auto-oriented neighbourhoods (Cervero, 1996).
Investment in the strategic road network can lead to changes in the spatial pattern of development and induced traffic demand is partly reflected in the spatial distribution of activities over the long term (Noland and Lem, 2001; Boarnet, 1998; Chandra and Thompson, 2000).
With respect to public transport, research from the San Francisco Bay Area shows that the availability of vacant and developable land is an important predictor of whether land-use changes will occur near public transport stations. In this case, the Bay Area Rapid Transit (BART), in and of itself, was not able to induce large-scale land-use changes but under the right circumstances (i.e. available land) it appeared to be an important contributor to new development (Cervero and Landis, 1997).
Transit Oriented Development refers to the practice of encouraging high-density, mixed-use development within a short walking distance of a public transport station and often includes specific measures, such as reduced parking, to encourage public transport use. Three conditions are necessary for such development to occur successfully: (1) favourable zoning policy, (2) sites attractive to developers, and (3) a strong development market. Where one or more of these does not apply, development may not follow transit provision.
Development clusters – selective expansion and new communities – are encouraged along the public transport network (Hall and Ward, 1998), potentially linked together at the regional and international scale to form agglomerations of polycentric cities (Hall and Pain, 2006).
Further reading here
Milton Keynes / South Midlands - Northamptonshire County Council has obtained funding to build a bus rapid transit system between Wellingborough and Northampton. Luton Borough Council is developing a rapid transit Busway between key housing and employment centres.
Greater Manchester - The Association of Greater Manchester Authorities has developed a transport strategy that embodies a corridor planning approach, based on 15 radials, each of which contains a major public transport facility – rail, tram or bus rapid transit.
Northstowe, South Cambridgeshire - The 25km Cambridgeshire Guided Busway will provide a viable alternative to driving between Cambridge and St. Ives/Huntingdon and is an integral part of the new Northstowe development. Crucially it is being provided in advance of the new development.
North East of England - The Tees Valley Joint Strategy Unit has developed a sub-regional transport strategy with input from 5 local authorities. Both the transport strategy and the general city region work strongly encourage a multi-modal view of the strategic transport network.