The findings of a U.S. study could have implications on Canadian pavement design. Using stiffer pavements on roadways could reduce vehicle fuel consumption by three per cent, and decrease carbon dioxide (CO2) emissions by 46.5 million metric tons, saving up to 237 million barrels of crude oil annually.
Professor Franz-Josef Ulm and PhD student Mehdi Akbarian at Massachusetts Institute of Technology (MIT) conducted a study using mathematical modelling instead of road experiments to look at the effect of pavement deflection on fuel consumption. They modelled physical forces when rubber tires rolled over pavement and found that because of the way energy is dissipated, the maximum load deflection is behind the path of travel—making the tires drive continuously up a slope, increasing fuel use.
“We’re wasting fuel unnecessarily because pavement design has been based solely on minimizing initial costs more than performance—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 explained. “We can now include environmental 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.”
Ulm and Akbarian input their data on 5643 representative sections of roads from U.S. Federal Highway Administration (FHWA) data sets, which included information on pavement and soil surface and subsurface materials, and number, type, and weight of vehicles using the roads. They also calculated and incorporated the contact area of vehicle tires with pavement.
The authors estimate the combined effects of road roughness and deflection are responsible for an annual average extra fuel consumption of 26,498 to 34,069 L (7000 to 9000 gal) per lane-mile on high-volume roads (not including the most heavily travelled roads) in the 8.5 million lane-miles making up the U.S. roadway network. They say up to 80 per cent of that extra fuel consumption, in excess of the vehicles’ normal fuel use, could be reduced through improvements in the basic properties of asphalt, concrete, and other materials used to build the roads.
Cement Association of Canada’s (CAC’s) Sherry Sullivan told Construction Canada Online the study results confirm financial and environmental arguments for using rigid, concrete pavements on roads in Canada or the United States. She explained based on the three per cent reduction in vehicle fuel consumption shown by the study, if all the 27,608 km (17,155 mi) of core routes in the Canadian National Highway System had been paved with concrete, annual fuel savings could now be in excess of $491 million, given today’s cost of diesel and CO2 reductions in excess of 1 million tonnes annually. This is equivalent to taking approximately 210,000 cars off the road or the carbon sequestered by over 27 million tree seedlings grown for 10 years.
“There are additional benefits too of course—concrete pavements last longer and require less maintenance than flexible asphalt pavements, they are cost-effective over their longer service life and competitive on initial costs, and they are produced locally, therefore representing a very sound value indeed,” said Sullivan.