Stiffer Roadways = Better Fuel Economy?

A vehicle's tires deform the pavement they roll over such that they are constantly moving slightly uphill, according to civil engineers at the Massachusetts Institute of Technology.

The effect is subtle. But the researchers say it causes America's vehicle fleet to burn about 273 million barrels of crude oil per year or at least 7,000 gallons of gasoline per lane-mile on roads with high traffic volume. They say improving the properties of asphalt, concrete and other materials could reduce that usage by as much as 80%.

Prof. Franz-Josef Ulm and doctorate student Mehdi Akbarian considered such variables as pavement thickness, stiffness, subsoil, vehicle type and vehicle weight. They found that the maximum deflection caused by a rolling tire pressing down on the road surface occurs behind the center of the tire's contact patch, thus producing a slight upward slope.

Ulm and Akbarian, whose work was done through an MIT unit sponsored by the Portland Cement Assn., estimate that stiffer road surfaces could cut fuel costs $15.6 billion per year and reduce the country's annual carbon dioxide emissions by more than 46 million metric tons.

The team used mathematical modeling rather than physical experiments to study the physical forces at work. They say their statistical approach avoids variations caused by real-world testing and enables a more accurate assessment of potential fuel savings across America's 8.5 million lane-miles of roadways.