Thursday, October 18, 2012

Driving and the Built Environment

Is there nothing we can learn from the past?  Why is the behavior of self-selectors so easily dismissed?  Why must the definition of mixed-use be so narrowly defined?  Is it unreasonable to believe that economic conditions stand to change greatly during a period of resource contraction?  These are some of the questions that repeated themselves in my mind as I read and analyzed the Transportation Research Board’s special report ( that attempted to definitively correlate compact development to a reduction in vehicular miles traveled, and by extension, to a reduction in energy consumption and emissions.

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  Unfortunately they come to no conclusion after dismissing previous transportation studies as outdated and citing an inadequacy in the number and quality of studies related to non-motorized transportation.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 (

The primary findings and recommendations of the report are as follows:


  1. Developing more compactly, that is, at higher residential and employment densities, is likely to reduce vehicle miles traveled (VMT).
  2. 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.
  3. More compact, mixed-use development can produce reductions in energy consumption and CO2 emissions both directly and indirectly.
  4. 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.
  5. 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.
  6. 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 study.


  1. Policies that support more compact, mixed-use development and reinforce its ability to reduce VMT, energy use, and CO2 emissions should be encouraged.
  2. 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.
    1. Longitudinal studies
    2. Studies of spatial trends within metropolitan areas
    3. Before and after studies of policy interventions to promote more compact, mixed-use development
    4. Studies of threshold population and employment densities to support alternatives to automobile travel
    5. Studies of changing housing and travel preferences
The research council is rather reluctant to draw conclusions or advocate for significant adjustments to national cultural arrangements despite developing a correlation between residential density and VMT.  Many statements are made in defining Finding 2 that support additive layers of density enhancement that would push VMT reduction to the high end of the predictive range, but that also beg questions about the ways these elements are defined and the exclusion of certain others.

Increasing residential density alone will have little to no effect on VMT as long as large swaths of land are relegated to single-use zones as is acknowledged in Finding 5.  Questions arise from the report’s (and the general consensus) interpretation of mixed-use and the jobs-housing balance.  While I will admit that organic emergent urbanism created some untenable relationships between residents and heavy industrial sites from a health and safety standpoint, I would argue that this was still a more vibrant urbanism that allowed for a less energy intensive existence at the household level.  Now the pendulum has swung too far in the opposite direction.  Contemporary light industrial endeavors re-integrated into residential zones would augment one’s ability for transit or non-motorized commuting.  Mixed-use in today’s parlance seems to imply a rigid proportion of retail and residential, some office space often the only departure from the paradigm.  An eye to this type of potential utilization should become a bigger part of adaptive re-use efforts in order to diversify employment opportunities in reinvestment districts.  This will require a reversion of legislation that has made integrated communities, like the one seen at left, illegal.

The issue of adjusting for self-selection as it pertains to transportation preference and habit dominates the literature review somewhat unfairly.  It has been stated, most recently in George Washington University’s, ‘DC: The WalkUP Wake-Up Call (,’ that demand for real estate in pedestrian-friendly urban neighborhoods significantly exceeds supply.  Shifting demographics and preference is one factor that the report acknowledges itself lacking as it pertains to the ability to interpret future trends.  Does the motivation of a resident of compact development devalue the neighborhood contribution toward reduced resource consumption?  Doesn’t policy play a major role in incentivizing behavior?  Would self-selection be so easily dismissed if it were a strategic decision rather than preference?

In closing, there must be a point at which the growing number of self-selecting individuals who prefer to avoid personal vehicular transportation becomes statistically significant enough that it cannot be dismissed as minority behavior.  Suburbanization was greatly aided by subsidizing the vast expansion of road capacity, mortgage availability and tax modification, zoning, and plentiful cheap energy.  One can envision a growing cohort of households which self-select due to economics rather than preference in a financial environment characterized by credit and capital scarcity.  These conditions undermine the ability to purchase, insure, maintain, and own personal vehicles.

1 comment:

Mike said...

In addition to quantifying the benefits of higher density in terms of reduced VMT and CO2 emissions, it'd be helpful if someone would calculate the economic savings over time; for the household, the municipality, and the country as a whole.

People don't pay much attention to CO2, land and oil consumption unless there is a very personal dollar figure attached to it.