Summary of paper by Larry Frank, Assistant Professor, Georgia Institute
This study documents how land use impacts both household travel choices and
vehicle emissions. The paper finds that people in areas of the region with higher
employment density, residential density and street connectivity (the number of
street blocks per unit of area) drive and pollute less on a daily basis. This
relationship proved to be true even when controlling for income, household size,
and the number of vehicles owned per household. The most interconnected street
network is situated upon a grid pattern, while the most disconnected pattern of
street layout is based on the dead-end or cul-de-sac These findings indicate that
both proximity and connectivity are required to reduce vehicle miles/hours of
travel and vehicle trips.
This study provides evidence that land use policies are required for the long-term
reduction of traffic congestion and improved air quality. The inability to modify
current land development practices will likely undermine other ongoing efforts to
reduce traffic congestion and emissions. Findings from this study provide direction
for altering local land use actions to reduce vehicle dependence and emissions.
Matching Growth and Regional Transportation Regional efforts
improve traffic and air quality conditions need to focus growth on existing
and emerging centers in a manner that achieves higher levels of density and
land use mix, and provides the infrastructure for a pedestrian environment.
Regional transportation investments targeted at increasing the desirability
and accessability of carpooling, transit, and non-motorized travel will have
limited effect on altering travel patterns and reducing mobile source
emissions without these supportive land use policies.
One Size Does Not Fit All Land Use Strategies are required
the unique social and physical characteristics of central, suburban and ex-
urban areas of the region. Strategies are required to address the unique sets
of issues associated with retrofitting existing communities, such as
providing quality pedestrian and bicycle linkages between existing
residential, office, and commercial uses already located in proximity to one
another. In emerging communities, it is critical to provide alternatives to
auto travel. This can be achieved by locating residential, commercial and
recreational areas near developing transit corridors.
Comprehensive Approach Land use policies required to reduce auto dependence need
to encourage both proximity and connectivity. Travel distances can be lessened through
the consolidation and intermixing of uses and the provision of increased pedestrian
connectivity and linkages between uses. Increasing the levels of density and land use mix
alone will not yield effective changes in travel patterns.
Demographic Factors It is critical to recognize the
underlying forces that manifest
themselves through community development patterns. Land use strategies to combat
congestion and air pollution will be ineffective if they are not accompanied by incentives to
spatially match housing types and labor markets and to address the effects of schools and
perceived levels of crime in residential locations.
Education and Empowerment The general public needs to
be made aware of the
hidden costs of current development practices and the potential benefits to the quality of
life that can be achieved through land use reform. Moreover, we need to get across the
fact that being stuck in traffic is linked with large lot, cul-de-sac subdivision planning
practices and that reduced traffic congestion, better air, and better physical health can be
achieved without giving up single family dwellings with private yards.
The study concludes that households located in areas that are more compact
in nature and inter-
connected with commercial and/or employment districts are less auto dependent. The research
presented here indicates that moderate increases of two to five dwelling units per acre can be
linked to significant reductions in vehicle miles traveled and decrease the generation of harmful
emissions including NOx, carbon monoxide (CO), and volatile organic compounds (VOC).
Furthermore, moderate increases in street connectivity are also associated
with reductions in
driving and air pollution per household. However, increasing residential or employment densities
or the level of street connectivity alone will likely yield little change in travel choice. Instead, land
use changes need to be made within the context of accessible transit service for regional travel and
high quality pedestrian environment to encourage walking. Land use reform, regional transit
investment, and an improved walking environment need to go hand in hand. Given these
qualifiers, the results of this study indicate that the improvement of Atlanta's air quality can be
partially achieved through the alteration of current land use practices.