Planning for Sustainable Travel

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Empirical Evidence

There is a very rich body of research covering the urban structure and traffic demand topic. Much of this, however, is US-based. There is comparatively little evidence covering the UK experience. Much of the literature, particularly the early research, has been simplistic in methodological approach. The early analysis (Newman and Kenworthy, 1989; Gordon and Richardson, 1989; Cervero, 1989 and 1996; Breheny and Rookwood, 1993; and Ewing, 1995) was pioneering and illuminating, but often open to several interpretations. It tended to be inconclusive and causalities remained largely unproven.

Important contributions were made in the UK on the role of density and settlement size (Ecotec, 1993; Banister et al, 1997) and location (Curtis and Headicar, 1994; Headicar, 2003). Stead (2001), using NTS data at the UK level, shows that socio-economic determinants of travel behaviour change are more important than land use factors, accounting for some 21%-58% of the variation in distance travelled. However land use factors are important, accounting for up to 27% of the variation in distance travelled at the local area level.

The latest research on this topic is providing more clarity in statistical terms, with a focus on multi-variate analysis and some assessment of the more difficult empirical issues, such as co-linearity (variables are inter-related), causality (impacts may be two-way) and attitudinal/self selection issues (whether particular urban forms are associated with certain travel behaviours, or whether people with particular types of attitude are attracted to certain urban forms). Some of the recent authors here are Bohte et al (2009), Naess (2009), Cao et al (2009), Levinson and Krizek (2008), Hickman and Banister (2007), Aditjandra et al (2007), Schwanen and Mokhtarian (2005), Handy (2005), Handy et al (2005), Krizek (2003), Ewing and Cervero (2001), Boarnet, and Crane (1999), Kockelman (1997) and Kitamura et al (1997).

The wide ranging potential of urban structure – including issues of density, settlement size, regional structure and accessibility, provision and mix of land use, jobs-housing balance, location, local street layout and neighbourhood design – covers interventions at a range of scales. It is clear that there are significant associations between the built environment and travel behaviour, even when socio-economic characteristics and attitudes have been accounted for. Trip lengths and mode share are the most likely of the travel variables to be affected by the form of the built environment.

Typical Coverage of the Literature

Urban Structure/ Socio-Economic Variable Travel “Dependent” Variable Method of Analysis
  • Density
  • Settlement size
  • Provision and mix of land use, jobs housing balance
  • Location
  • Regional structure and accessibility
  • Local street layout, neighbourhood design, parking
  • Socio-economic characteristics
  • Attitudinal and cultural characteristics
  • Traffic volume
  • Number of trips
  • Travel distance
  • Mode
  • Car ownership
  • Journey purpose, e.g. journey to work, non-work travel
  • Congestion
  • Energy consumption
  • CO2 emissions
  • Electronic social interaction rather than physical travel
  • Theoretical argument
  • Descriptive analysis
  • Bi-variate analysis, e.g. correlation analysis
  • Multi-variate analysis, e.g. regression analysis
  • Simulation, e.g. modelling, including land use and transport integration models
  • Various datasets, e.g. aggregate and disaggregate level travel surveys
  • Some limited longitudinal analysis, but mainly cross sectional data used

The impact of changes in the price of travel, and wider issues such as housing availability and price relative to income, availability of transport infrastructure and traffic demand management regime, remain poorly understood in terms of the land use/transport interaction debate. To analyse the more complex temporal relationships requires longitudinal data, allowing the dynamic processes to be explored by tracking individuals, households and businesses over time. This is one of the areas where future research can be focused. Much of the current available analyses are based on cross sectional data, allowing a view of one ‘snapshot’ in time.

Key Themes: Practical Steps and Actions

Alongside the academic evidence, there are guidelines that practitioners can follow to help achieve sustainable travel. These are elaborated in terms of key themes listed to the top left of the page.

Further reading here

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

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