THE AVERAGE AMERICAN FAMILY devotes more than half of its income (52 percent) to housing and transportation combined, according to a study put out by the Surface Transportation Policy Partnership and the Center for Neighborhood Technology, two nonprofit research groups that crunch Bureau of Labor Statistics data. But the proportion a family allocates to one versus the other varies by market, and research suggests that the amount a family spends on transportation may be in many cases inversely proportional to what it spends on housing.

Houstonians, who endure the highest commuting costs in the nation, devote roughly 21 percent of their income to transportation and 32 percent to housing, according to the study, “Driven to Spend,” while San Francisco residents spend only 16 percent getting to work, but a heftier 38 percent on housing. In Cleveland, the second most-expensive commuter city, residents fork over 20 percent for commuting costs and 33 percent for shelter. New Yorkers, who inhabit one of the nation's least-expensive commuter cities, spend only 15 percent on transportation, but fork over 38 percent for the roofs over their heads.

Transportation costs are often lowest in metro areas with well-established mass transit systems, according to the study, which tracked expenses related to gas, tolls, public transit fares, car payments, and auto maintenance in 28 major metro areas. Researchers noted four of the five cities with the lowest transportation costs as having “large” or “extensive” rail systems, while five of the six cities with the highest transportation costs were found to have small, start-up, or nonexistent rail systems.

The study authors further noted that a low-income, workforce family's ability to afford housing is significantly affected by higher transportation costs, since commuting expenses gobble up a larger proportion of the family budget. In locales where public transit options are sparse and cars are the predominant mode of transportation, such families may be especially vulnerable to volatile spikes in gas prices. Here's hoping those don't come in tandem with ARMS that are kicking into high gear.

FOR A BREAKDOWN OF HOUSING AND TRANSPORTATION EXPENSES BY U.S. METRO AREA, VISIT OUR WEB SITE AT WWW.BUILDERONLINE.COM, CLICK ON “THE MAGAZINE” TAB, AND THEN CLICK ON THE NOVEMBER ISSUE.