But until recently, the increase in gas prices has not been reflected in diminished gasoline consumption. Earlier this month, the Wall Street Journal reported that gas consumption had fallen 1.1% in the first six weeks of 2008, compared to the same period last year — the first time in 16 years that gas consumption had slackened. The Journal wrote that “there is evidence that Americans are changing their driving habits and lifestyles in ways that could lead to a long-term slowdown in their gasoline consumption,” citing moves towards downtown living and more fuel-efficient vehicles.

Preliminary data from the Federal Highway Administration’s Traffic Volume Trends also shows a shift in travel behavior, with national Vehicle Miles Traveled for 2007 dropping by 0.4% compared to 2006 numbers.

Economist and TSTC board member Charles Komanoff has pointed out that gas prices are more elastic than these raw consumption and VMT figures indicate. In an analysis factoring in gross domestic product as a measure of the economy, he finds that a 10% increase in gas prices results in a 2% decline in gas consumption, and suggests that the effect of higher prices on demand had been hidden by economic growth, which until recent months had been strong. Had oil prices not risen, gasoline use over the last few years would have been higher than it was.

So maybe, as the Journal suggests, Americans are finally responding to higher gas prices by driving less and trading in their SUVs for more fuel efficient vehicles. Sales of light trucks, a category which includes pickup trucks and SUVs, were 19% lower in January 2008 than in January 2007. Large car sales fell by 26.5% in the same time frame, while small car sales rose by 6.5%.

A recent article from New Jersey Future argues that New Jersey’s ample transit service and compact development patterns leave the state well-positioned to respond to rising gasoline prices because a relatively high proportion of residents have the option of leaving their car at home. The same argument can be made for New York City and the tri-state region’s more transit-friendly communities. Unfortunately, few places in the United States have the transit service and compact, walkable and bikeable communities needed to accommodate a shift in travel behavior.

The obvious lesson to glean from these trends is that auto-centric planning is becoming increasingly irrelevant to economic realities. As transit agencies must adapt to a potential age of climate change and peak oil, so too must planners. Not doing so will eventually leave residents in an economic bind, with no short-term way out.