The quantity of vehicular miles traveled (VMT) in 1985 represents an approximate 40% decline from 2010 levels. The ability to achieve such a reduction, or one even more significant, is dismissed by this study as nearly impossible, despite their inclination to find a large negative elasticity between the two factors. While overtly recognizing the national development pattern as unsustainable (“…these dispersed, automobile-dependent development patterns have come at a cost, consuming vast quantities of undeveloped land; increasing the nation’s dependence on petroleum, particularly foreign imports; and increasing greenhouse gas emissions that contribute to global warming.”), the board was unwilling to declare suburbanization a reversible trend. They were also overly eager to dismiss self-selective behavior, presumably as an oddity or minority behavior, instead of recognizing its potential indicative qualities or its contribution to VMT decline.
Credit is due to the research council for tacking onto their mandate the question of determining density thresholds that would enhance transit feasibility. Unfortunately they come to no conclusion after dismissing previous transportation studies as outdated and citing an inadequacy in the number and quality of studies related to non-motorized transportation. Also unfortunate is the politicization inherent in the report’s representation of energy dependence as simply a cost/security issue. While more palatable to the report’s direct intended audience, this does not respect the urgency related to potential resource unavailability as touched upon in the University of Utah Metropolitan Research Center’s response (http://www.smartgrowthamerica.org/documents/ResponsetoTRBSpecialReport.pdf).
The primary findings and recommendations of the report are as follows:
- Developing more compactly, that is, at higher residential and employment densities, is likely to reduce vehicle miles traveled (VMT).
- The literature suggests that doubling residential density across a metropolitan area might lower household VMT by about 5 to 12 percent, and perhaps by as much as 25 percent, if coupled with higher employment concentrations, significant public transit improvements, mixed uses, and other supportive demand management measures.
- More compact, mixed-use development can produce reductions in energy consumption and CO2 emissions both directly and indirectly.
- Illustrative scenarios developed by the committee suggest that significant increases in more compact, mixed-use development will result in modest short-term reductions in energy consumption and CO2 emissions, but these reductions will grow over time.
- Promoting more compact, mixed-use development on a large scale will require overcoming numerous obstacles. These obstacles include the traditional reluctance of many local governments to zone for such development and the lack of either regional governments with effective powers to regulate land use in most metropolitan areas or a strong state role in land use planning.
- Changes in development patterns significant enough
to substantially alter travel behavior and residential building efficiency
entail other benefits and costs that have not been quantified in this
- Policies that support more compact, mixed-use development and reinforce its ability to reduce VMT, energy use, and CO2 emissions should be encouraged.
- More carefully designed studies of the effects of land use patterns and the form and location of more compact, mixed-use development on VMT, energy use, and CO2 emissions should be conducted so that compact development can be implemented more effectively.
- Longitudinal studies
- Studies of spatial trends within metropolitan areas
- Before and after studies of policy interventions to promote more compact, mixed-use development
- Studies of threshold population and employment densities to support alternatives to automobile travel
- Studies of changing housing and travel preferences