Based on the sustainable development agenda and the evidence base of built-environment and transportation relationships, policy responses have evolved to reduce vehicle miles by private transport and promote public transport and non-motorised travel. The planning policy tools to achieve this involve land use, transport and urban design measures. Land use measures include controlling new development, densities and mix of uses. Transport measures include public transport services, road space allocation between modes, traffic calming, parking policy and new infrastructure. Urban design measures include street layouts, public space provision and architectural design. Sustainable urban planning depends on integrating these various elements synergistically together.
This research focuses on city-wide interactions between land use, transportation networks and accessibility. Local scale aspects of transportation planning and urban design are considered here only tangentially, yet this is not to imply these factors are insignificant, as they have very significant roles to play (Cervero, 1998; Urban Task Force, 1999).
The „elephant in the room‟ for sustainable transport policy is typically fuel taxation which, as the previous international review of transportation energy use highlighted, is likely to be the most influential policy lever in influencing long term private vehicle use. Fuel taxation is however beyond the control of city governments and transport planners. At national level where taxation policy is determined, increases in fuel duty of the scale required to produce significant behaviour change typically have strong political opposition. Furthermore there are issues with the „blunt instrument‟ of fuel taxation which cannot differentiate costs spatially or temporally. Pricing tools have been developed to better target private vehicle costs in areas of extreme congestion, with London‟s congestion charging scheme being a notable example, though these remain atypical cases at present.
A milestone land use planning policy document in the UK was Planning Policy Guidance Note 13 (DoE 1994) which established the core goals of
concentrating higher density development at public transport nodes, allocating
isolated from public transport, avoiding small new settlements, and promoting a mix of commercial and residential uses where feasible. This approach was expanded on to connect density levels and public transport services to a hierarchy of urban centres, as proposed in the Urban Task Force (1999) report (Figure 3.28).
Figure 3.28: Plans for a Transit Orientated City. Source: Urban Task Force (1999).
In cities with a strong history of public transport use, such as major European cities, the hierarchy of town centres envisaged in Figure 3.23 are, to a greater or lesser extent, already in place, having emerged in the 19th and early 20th
centuries around railway and tram networks. For these cities planning priorities generally involve the improvement and better integration of existing services and the directing of new development to existing or integrated newly-built centres. Greater challenges exist where transit orientated structures have to be
„retro-fitted‟ on to automobile dominated cities. A conceptual diagram for such a process by Newman and Kenworthy (1999) is shown in Figure 3.29. When one considers the costs in terms of new infrastructure development and potentially land purchasing for such a process, in addition to established infrastructure and lifestyles built around car travel, clearly the challenges for this model are vast.
Figure 3.29: Transit Infrastructure Plan for Automobile Cities.
Source: Newman and Kenworthy (1999).
Amongst planning researchers concerned with sustainable development there is a strong consensus around the nodal development ideas described above, but there are differing views within this general approach. There have been critiques of urban models that are dominated by the city centre, and that overly
monocentric structures bring long distance one-way congested travel patterns (Maguire et al., 2004). The alternative is for a „flatter‟ hierarchy of centres through polycentric structures, achieved through processes of „decentralised concentration‟ leading to larger sub-centres with more advanced employment roles. This is broadly similar to the network city model (Meijers, 2007) described earlier in Sub-Section 2.2.4.
3.5 Chapter Conclusions
This chapter set out to address Research Aim 2, which was “to define urban sustainability in relation to the transportation sector, and analyse evidence on the links between urban form and transportation environmental impacts”. We defined sustainability narrowly in terms natural resource management, ecosystem preservation and mitigating anthropogenic climate change.
Transportation is amongst the largest sectors of energy consumption and carbon emissions, and has increased in relative terms as carbon emissions have fallen in other sectors. These increases have been caused by a five-fold increase in travel distances since 1960, overwhelmingly through increased car use, as individuals have sought to maximise their spatial opportunities in housing, employment, social and other activities. We concluded that the empirical analysis of transportation sustainability needs to focus on the two key issues of mode-choice and travel distances, as these factors underpin energy use and carbon emissions.
Urban form has been promoted as a means to achieving greater urban
sustainability in travel patterns. There is massive international variation in per-capita transportation energy use and this variation is correlated with measures of urban form such as densities. The empirical research evidence however reveals complex cross-correlations between socio-economic, urban form and
accessibility variables at various scales. Whilst the most sustainable cities are overwhelmingly high density, it is questionable whether urban form measures have a direct causal role in determining travel patterns, with socio-economic factors such as income, fuel taxation and car ownership being amongst the most influential in statistical models. The research evidence supports the theoretical argument that accessibility is the key geographical factor influencing travel patterns. Urban form measures such as density and land use influence absolute and relative accessibilities by various modes, as do transportation infrastructure and policies related to fares, fuel taxation and parking. The most sustainable cities achieve synergies between land use, transport, taxation, built-environment and cultural factors, and urban research needs to embrace this comprehensive
scope rather than narrowly focussing on any one particular aspect of urban structure.
What then are the consequences of these conclusions for the empirical measurement of urban structure and transport sustainability undertaken in the following chapters? Firstly we need to measure a comprehensive range of socio-economic, built-environment and accessibility dimensions, as these all have relationships with travel patterns. Key socio-economic factors include income, household structure and car ownership, whilst key built-environment factors include density and land use. These factors need to be considered in
combination with accessibility measures, as accessibility drives property markets (as discussed in Chapter 2) and is closely connected to land use and socio-economic housing market outcomes. In terms of how accessibility should be measured empirically, several conclusions stand out from the review. These are the importance of regional accessibility (identified as the most influential factor in the meta-analysis in Section 3.3.4); the need to measure both trip origin and trip destination accessibility with arguments that trip destination measures may be more influential; and finally the desirability of more accurate accessibility measures based on network analysis.
The review has also identified a number of areas where research evidence is thin and additional analysis is needed. Given that regional accessibility is identified as being highly influential in statistical modelling, it is problematic that there is a lack of studies taking a comprehensive regional approach. This means that important questions regarding the sustainability and efficiency of city-region structures, such as monocentric and decentralised forms, cannot be sufficiently assessed. This research thesis advocates a meso-scale intra-metropolitan analysis as the most appropriate means of incorporating the influence of regional accessibility (and other regional housing and labour markets) into sustainable travel research, thus providing relevant evidence for strategic planning policy. Further to the point of research knowledge gaps, there is also a distinct lack of analysis exploring how employment dynamics and agglomeration (identified as central to changing urban structure in Chapters 1
destination points, as well as the wider need to incorporate findings from economic geography into sustainable travel analysis. Analysing the
relationships between employment geography and travel patterns is central to the research in the following chapters.