Driving and the Built Environment

The long awaited TRB report "Driving and the Built Environment: The Effects of Compact Development on Motorized Travel, Energy Use, and CO2 Emissions" was released today.

About the TRB Report


We’re excited that TRB took on the important work of examining the contribution that development patterns play in climate change and our energy usage, concluding that ‘policies that support more compact, mixed-use development and reinforce its ability to reduce VMT, energy use, and CO2 emissions should be encouraged.’ Since nearly a third of greenhouse gas emissions and 70 percent of our oil use are from the transportation sector, we’re not going to be able to reach our climate and energy goals without reductions in vehicle miles traveled.

The report confirms what the dozens of studies before it showed, as well: that making our communities more walkable, connected, and with better transportation choices can make a significant dent in greenhouse gas emissions, oil usage, and vehicle miles traveled. And the report finds, as real world communities have, that the other benefits of moving to more smart growth-oriented development are significant: ‘More compact, mixed-use development should reduce some infrastructure costs, increase the feasibility and cost-effectiveness of public transit, and expand housing choices where compact developments are undersupplied. Other benefits include less conversion of agricultural and other environmentally fragile areas and greater opportunities for physical activity by facilitating the use of nonmotorized modes of travel, such as walking and bicycling.’

The report rightly concludes that increasing density levels in our communities isn’t the only answer, but that to best reduce vehicle miles traveled rates, we need a comprehensive solution. Research by University of Utah professor Reid Ewing, who reviewed more than 50 vehicle miles traveled studies for his book Growing Cooler made the same conclusion: residential and employment densities were actually less important as a determinant of VMT levels than other factors such as accessibility to jobs and other destinations. Additionally, having a mix of uses in communities (like housing near shops, etc.) and a well-designed street network with sidewalks are just as important as density levels to VMT reduction.

The important number in the report is the estimate that coupling more compact development with better street connectivity, public transportation improvements, and other complementary measures, would result in a 25 percent reduction in vehicle miles traveled. That type of reduction would have a comparable level of reduction in greenhouse gas emissions per increment of new development.

The Center for Clean Air Policy has done research showing that even with the progress we’ve made on fuel efficiency standards and low carbon fuels, a major factor driving the increasing levels of GHG emissions from the transportation sector are the inefficient, sprawling development patterns of many American communities. For example, the number of miles Americans drive has grown three times faster than the U.S. population since 1980. CCAP estimates that even with the higher fuel efficiency standards passed by Congress last year and a low carbon fuel standard implemented nationwide, projected vehicle miles traveled increases would still leave us far above our climate targets for the transportation sector by 2030.

The TRB report makes a conservative projection about the impact that development patterns can make on vehicle miles traveled and climate change emissions, but underestimates the popularity and potential of strategies to help people drive less, while accomplishing more in their daily lives. The average American spends 100 hours in their car every year just commuting to work alone, and spends nearly 20 percent of their household budget on transportation costs. Fifty percent of Americans lack access to regular, quality public transportation.

The report is right that change is never easy, but Americans are clamoring for more convenient, walkable neighborhoods that offer the opportunity to spend less time in their cars. A 2004 Survey by Smart Growth America and the National Association of Realtors showed that 6 in 10 prospective homebuyers chose walkable neighborhoods with less time spent driving. Transit ridership reached its highest level last year since the 1950’s. And with an aging population and more households without children, these trends towards living in places closer to downtowns and near public transportation, are only projected to increase in the future.

Finally, the report underestimates the data and real-world examples showing clearly that significant reductions in vehicle miles traveled result from better designed, more walkable communities with real transportation choices. More than 200 studies have been conducted in recent years on the connection between development patterns and vehicle miles traveled, and there are examples around the country of communities that have seen reductions in VMT, greenhouse gas emissions, and oil usage due to better community design. Here’s just a sampling:



· Portland has a 20 percent lower vehicle miles traveled per capita, due to its investment in walkable, compact neighborhoods and public transportation choices. At the same time, the city saves thee equivalent of $2.6 billion annually in gasoline and time because of these measures, according to a CEOs for Cities report.



· In Georgia, the Atlantic Station redevelopment project in Atlanta has 30 percent lower driving rates compared to surrounding developments.



· A Seattle study found that households located in the most interconnected areas of the city generated less than half the VMT of households located in the least-connected areas of the region, holding true after adjusting for household size, income, and vehicle ownership.



· A study in the Bay Area of California by the Metropolitan Transportation Commission found that for people who both live and work within a half-mile of a rail or ferry stop, 42 percent commute by transit. For those who neither work nor live near these transit stations, only 4 percent commute by transit.



· The Center for Neighborhood Technology has an analysis of the CO2 levels per acre and household for 55 regions. Looking at the CO2 per household figures for each of the regions clearly shows the dramatic difference between center cities and out-lying suburbs, due to increasing amounts of auto travel: http://htaindex.cnt.org



Additional critiques of the study

The study’s more ‘moderate’ scenarios, which estimate reductions of only 5-12 percent less driving in more compact development, are out of touch with the reality of how much less people drive in areas that are smart growth oriented, versus business as usual development. The study itself estimates that the average reductions that are possible through smart growth development is a reduction of 25 percent, and Growing Cooler (based on a meta-analysis of dozens of VMT studies) found an average of 20-40 percent VMT reductions in smart growth versus typical sprawl developments.


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Kate Rube
Policy Director