CAMBRIDGE, Mass. -- A new study by civil engineers at MIT shows that using stiffer pavements on the nation's roads could reduce vehicle fuel consumption by as much as 3 percent a savings that could add up to 273 million barrels of crude oil per year, or $15.6 billion at today's oil prices. This would result in an accompanying annual decrease in CO2 emissions of 46.5 million metric tons.
The study, released in a recent peer-reviewed report, is the first to use mathematical modeling rather than roadway experiments to look at the effect of pavement deflection on vehicle fuel consumption across the entire U.S. road network. A paper on this work has also been accepted for publication later this year in the Transportation Research Record.
By modeling the physical forces at work when a rubber tire rolls over pavement, the study's authors, Professor Franz-Josef Ulm and PhD student Mehdi Akbarian, conclude that because of the way energy is dissipated, the maximum deflection of the load is behind the path of travel. This has the effect of making the tires on the vehicle drive continuously up a slight slope, which increases fuel use.
The deflection under the tires is similar to that of beach sand underfoot: With each step, the foot tamps down the sand from heel to toe, requiring the pedestrian to expend more energy than when walking on a hard surface. On the roadways, even a 1 percent increase in aggregate fuel consumption leaves a substantial environmental footprint. Stiffer pavements which can be achieved by improving the material properties or increasing the thickness of the asphalt layers, switching to a concrete layer or asphalt-concrete composite structures, or changing the thickness or composition of the sublayers of the road would decrease deflection and reduce that footprint.
"This work is literally where the rubber meets the road," says Ulm, the George Macomber Professor in the Department of Civil and Environmental Enginee
|Contact: Denise Brehm|
Massachusetts Institute of Technology