Big Macs and big gulps have thus far played leading roles in America’s obesity blame game as covered by the national media. Some state governments, including California, have already begun charging a "fat tax" on snacks and soda. But are governments and others missing the big picture?

Medical research has shown that there is more to obesity than what one eats; gaining weight is also a matter of physical activity. Could our elected governments’ car-heavy transportation policies be as guilty in America’s obesity epidemic as Big Macs? Many health experts have suspected that spending hours sitting in cars, particularly in sprawling areas not negotiable by foot, contributes more to obesity than other modes of transportation including walking, biking or moving between bus and rail stops, which are not usually found in sprawling areas.

In a recent study by the Surface Transportation Policy Project, "Measuring the Health Effects of Sprawl," the sprawl-obesity hypothesis was backed by statistics for the first time. The analysis showed that residents of sprawling areas tend to weigh more and are more likely to be obese than those living in more densely populated areas. Other research has shown that those living in sprawling, more car-dependent areas do more driving and less walking than those in dense areas with public-transit .

The government escalated the car-based transportation system and related sprawl with the Eisenhower Federal Highway Act of 1956 and has since spent billions of Americans’ gas tax dollars building highways and enabling neighborhoods to move further out. Federal highway spending still outstrips alternative transit spending for rail, bus, sidewalks and bike lanes several times over. The result has been a reshaped society where the overwhelming majority of Americans now live in areas that are less welcoming to pedestrians and bicyclists than they are to cars. The Texas Transportation Institute’s "2003 Urban Mobility Study" shows that American urbanites are ever more tied to their cars, spending more time stuck behind the wheel and driving more miles each year.

Researchers are just now beginning to link the country’s transportation policies to our obesity, but it is unclear whether the general public is making that connection. Could some Americans be as addicted to cars as they are to cigarettes or to fatty foods? Cars are not physically addicting. But neither are Oreos and that has not stopped the public or the government from taking action.

Medical experts have warned that obesity is rapidly reaching epedemic proportions. But how at fault is our car-based transportation system, which Americans pay for each time they fill up?

Many might say this would just be another attempt of Americans to blame others for poor personal decisions. Others might say choices about how to get around town are a bit more limited than what to order for dinner.

Whatever the case, people are looking for someone to hold accountable for the country’s expanding waistline and weight-related health costs. Fat taxes and lawsuits against fatty food providers have been the first attempts at accountability.

Many, including the STPP researchers, say the state and federal governments should diversify their road diet with more sidewalks, bike lanes, and public transportation. It may also be time for government to take another look at the provisions in gas tax law.

Catherine Rentz-Pernot studies regional transportation issues for the Gulf Coast Institute.