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NEWS SCOPE RESEARCH ments. The mathematical model is there- fore based on the actual mechanical be- havior of pavements under load. To obtain their results, Ulm and Akbarian fed their model data on 5,643 representative sec- tions of the nation's roadways taken from Federal Highway Administration data sets. This data include information on the sur- face and subsurface materials of pave- ments and the soils beneath, as well as the number, type and weight of vehicles using the roads. The researchers also calculated and incorporated the contact area of ve- hicle tires with the pavement. Ulm and Akbarian estimate that the com- bined effects of road roughness and deflec- tion are responsible for an annual average extra fuel consumption of 7,000 to 9,000 gallons per lane-mile on high-volume roads (not including the most heavily traveled roads) in the 8.5 million lane-miles making up the U.S. roadway network. They say that up to 80 percent of that extra fuel consumption, in excess of the vehicles' nor- mal fuel use, could be reduced through im- provements in the basic properties of the asphalt, concrete and other materials used to build the roads. "We're wasting fuel unnecessarily because pavement design has been based solely on minimizing initial costs more than per- formance—how well the pavement holds up—when it should also take into account the environmental footprint of pavements based on variations in external conditions," Akbarian says. "We can now include envi- ronmental impacts, pavement performance and, eventually, a cost model to optimize pavement design and obtain the lowest cost and lowest environmental impact with the best structural performance." The researchers say the initial cost outlay for better pavements would quickly pay for itself not just in fuel efficiency and de- creased CO2 emissions, but also in reduced maintenance costs. "There's a misconcep- tion that if you want to go green you have to spend more money, but that's not nec- essarily true," Akbarian says. "Better pave- ment design over a lifetime would save much more money in fuel costs than the initial cost of improvements. And the state departments of transportation would save money while reducing their environmental footprint over time, because the roads won't deteriorate as quickly." "This MIT research pioneered a rigorous mathematical framework relating fuel con- sumption with mathematically predicted pavement deflection. This framework lays JULY 2012 | 23 a foundation for continued development and future improvement of advanced pave- ment-vehicle interaction models," says Lev Khazanovich, a professor of civil engineer- ing at the University of Minnesota not in- volved in this research. "Integration of the results of this study with the Mechanistic-Empirical Pavement Design Guide recently adopted by the American Association of State Highway Transportation Officials will enable trans- portation agencies to account for traffic fuel consumption in pavement design de- cisions. This makes Akbarian and Ulm's re- search especially important today in light of the efforts of transportation agencies to reduce the environmental footprint of the transportation system."