Early last week the State Smart Transportation Initiative, a sustainable transport program funded by the Department of Transportation, released some charts on the continued decline of vehicle-miles traveled in the United States. Overall VMT dropped 1.2 percent in 2011 from the previous year, reaching its lowest total since 2003, and per capita VMT fell 2.1 percent to levels not seen since 1998:
Researchers have been saying for several years now that cities in the United States and other developed countries may have reached "peak driving" — a level of vehicle miles at or near the saturation point. The idea is that the sheer volume of VMT can't possibly rise at the same rate it did in the second half of the 20th century, so mileage will either increase far more modestly than it has in the recent past, or perhaps even start to decline.
So far that prediction seems on point. SSTI notes a DOT study from 2006 [PDF] that estimated a rise of 50 to 60 percent in VMT from 2001 to 2025. That would be a significantly slower rise than over the previous 25-year period, 1977 to 2001, during which VMT rose 151 percent. But even this conservative estimate now seems incredibly generous: "In the first 10 years of the period, per capita VMT actually declined by nearly 3 percent," SSTI reports.
The 64-mile-per-gallon question is why. The simplified and convenient answer is often gas prices, and with today's New York Times reporting the "spector" of $5 a gallon fuel prices it may become a favored political one this election year. But an equally compelling reason is a rise in the embrace of sustainable land-use patterns. A brief analysis by SSTI found a weak connection between VMT and gas prices, and a rather strong one between vehicle miles and urban density:
The connection between land use and VMT continues to be debated, but the rationale behind it is sound. With a rise in urban density comes an ease of accessibility. On its own that would lead to an increase in trip-making, but accessibility also makes the length of each trip shorter and more direct, and creates a favorable situation for the use of non-automobile travel modes. "It is generally observed that greater accessibility associated with better transportation-land use coordination will result in lower VMT," the 2006 DOT study stated.
The logic harmonizes with some of the best research on "peak driving" to date. In a paper published last June [PDF] in the journal World Transport Policy and Practice, Australian researchers Peter Newman and Jeff Kenworthy presented the reversal of urban sprawl and the rise of urbanism as two of the six major reasons VMT has plateaued. Newman and Kenworthy examined the densities of a number of cities around the world from 1960 to 2005 and found that a turning point has been reached in previously auto-dependent cities. With the continued development of urban land use patterns, the researchers expect the growth of VMT to slow down as a result:
In an influential study of VMT released in late 2008 [PDF], the Brookings Institution examined travel behavior in the 100 largest metro areas in the United States and found evidence of lower per capita VMT rates in cities with high-density development and strong transit systems. On the flip side, unsurprisingly, places with low density have high levels of VMT. "These trends should force a hard look at the correlation between metropolitan development, accessibility characteristics, and the effects on VMT and auto ownership patterns," Brookings authors Robert Puentes and Adie Tomer concluded. It seems like they're doing just that.
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