Study Finds $15 Billion in Annual Fuel Savings From Building Roads With Harder Surfaces

This story appears in the March. 11 print edition of Transport Topics.

Building roads with harder surfaces could save more than $15 billion in annual fuel costs in the United States, according to a new study by researchers at the Massachusetts Institute of Technology.

The study examined the effect of pavement deflection, or the small dent in pavement that a vehicle creates as it moves across the surface of the roadway. The dent creates a slight but constant uphill climb, which burns more fuel.

Although the effect of deflection is very slight for individual vehicles, the aggregate effect on the entire road network can be significant, with trucks having notably larger changes in fuel consumption than passenger cars because of their heavier weights, the study found.

Stiffer pavements could reduce fuel consumption by as much as 3%, saving roughly 273 million barrels of crude oil a year and reducing emissions by 46.5 million metric tons, according to the study, which was conducted by MIT for the Portland Cement Association and the Ready Mixed Concrete Research and Education Foundation.

Larry Scofield, director of pavement innovation for the American Concrete Pavement Association and director of engineering and research for the International Grooving and Grinding Association, said the findings could accelerate a shift towards concrete pavements.

“With the ever-increasing cost of asphalt and the conversion of [asphalt] plants to more profitable gas-producing refineries, you will continue to see a market shift towards construction of more concrete pavements,” he said in an interview with Transport Topics.

Concrete roadways account for only 6% of all roads in the United States, according to a spokeswoman for the Portland Cement Association, based in Skokie, Ill.

The association helped to establish a Concrete Sustainability Hub at MIT in 2009.

There are a number of ways to achieve harder roadway surfaces, said Franz-Josef Ulm, a professor of civil and environmental engineering at MIT and co-author of the study.

“Stiffer pavements can be achieved by improving material properties or increasing the thickness of asphalt layers, switching to a concrete layer or asphalt-concrete composite structures, or changing the thickness or composition of the sublayers of the road,” Ulm said.

While concrete is inherently stiffer than asphalt, Ulm said, the research study “is not about asphalt versus concrete.”

“The ultimate goal is to make our nation’s infrastructure more sustainable. Our model will help make this possible by giving pavement engineers a tool for including sustainability as a design parameter, just like safety, cost and ride quality.”

Ulm said current methods to improve fuel efficiency are focused on switching to higher mileage vehicles or maintaining proper tire inflation, which are difficult to standardize.

Improving fuel efficiency through the design and maintenance of roadways can be controlled by governmental agencies that set standards for construction of streets and highways, he said.

The MIT researchers used data from 5,643 representative sections of roadways taken from Federal Highway Administration to test the behavior of pavements under load. The study is the first to use statistical analysis rather than actual roadway experiments to look at the effect of pavement deflection on vehicle fuel consumption across the entire U.S. road network.

“Previous empirical studies all looked at the impact of roughness and pavement type for a few nonconclusive scenarios, and the findings sometimes differed by an order of magnitude,” Ulm said. “Where do you find identical roadways on the same soils under the same conditions? You can’t. You get side effects. The empirical approach doesn’t work. So we used statistical analysis to avoid those side effects.”

Ulm said the combined effect of road roughness and deflection is responsible for an annual average extra fuel consumption of 7,000 gallons to 9,000 gallons per lane-mile on high-volume roads in the United States, where 8.5 million lane-miles are in the roadway network.

Up to 80% of that extra fuel consumption could be reduced through improvements in basic properties of the asphalt, concrete and other materials used to build the roads, said Ulm and fellow researcher Mehdi Akbarian, a doctorate student and co-author of the study.

“We’re wasting fuel unnecessarily because pavement design has been based solely on minimizing initial costs more than performance,” Akbarian said.

“Better pavement 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 wouldn’t deteriorate as quickly,” he said.