A recent study conducted by civil engineers at MIT found that using stiffer pavements on U.S. roads could cut vehicle fuel consumption by as much as three percent. That savings could add up to 273 million barrels of crude a year.
Stiffer roads also would reduce annual carbon dioxide emissions by 46.5 million metric tons, according to the study released in a recent peer-reviewed report. There’s no shortage of road studies. This is the first to use mathematical modeling rather than roadway experiments to evaluate the effect pavement deflection has on fuel consumption across the entire U.S. road network, MIT said in a release.
The study’s authors, Professor Franz-Josef Ulm and student Mehdi Akbarian, modeled the physical forces that occur when a rubber tire rolls over pavement. They contend that the energy is dispersed so that the maximum deflection of the load is behind the path of travel. This makes the tires on the vehicle drive continuously up a slight slope — and in turn, increases fuel use. Just like it takes more energy to walk in sand than on a hard surface, cars use more fuel when there’s constant upward slope to deal with.
Road roughness and deflection are responsible for an annual average extra fuel consumption of 7,000 to 9,000 gallons per lane-mile on high-volume roads in the 8.5 million lane-miles that make up the U.S. network. The authors says up to 80 percent of that extra fuel consumption could be reduced through improvements in the basic properties of asphalt, concrete and other materials used to build roads.
The research was conducted as part of the Concrete Sustainbility Hub at MIT, which is sponsored by the Portland Cement Association and the Ready Mixed Concrete Research & Education Foundation and has a goal of improving the environmental footprint of that industry, MIT said.
The authors say the study isn’t meant to pit asphalt against concrete. However, they also say stiffer pavements can be achieved by improving the material properties, increasing the thickness of the asphalt layers, switching to a concrete layer or asphalt-concrete composite structure, or changing the composition of the sublayers of the road. Concrete has its own problems. Its massive use contributes about 5 percent of global carbon dioxide production.
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