Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Civil engineers find savings where the rubber meets the road

23.05.2012
Study shows that pavement deflection under vehicle tires makes for a continuous uphill drive that increases fuel consumption

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 Engineering. "We've got to find ways to improve the environmental footprint of our roadway infrastructure, but previous empirical studies to determine fuel savings all looked at the impact of roughness and pavement type for a few non-conclusive scenarios, and the findings sometimes differed by an order of magnitude. 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."

The new study defines the key parameters involved in analyzing the structural (thickness) and material (stiffness and type of subgrade) properties of pavements. The mathematical model is therefore based on the actual mechanical behavior of pavements under load. To obtain their results, Ulm and Akbarian fed their model data on 5,643 representative sections of the nation's roadways taken from Federal Highway Administration data sets. These data include information on the surface and subsurface materials of pavements 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 vehicle tires with the pavement.

Ulm and Akbarian estimate that the combined effects of 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 (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' normal fuel use, could be reduced through improvements 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 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 says. "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."

The researchers say the initial cost outlay for better pavements would quickly pay for itself not just in fuel efficiency and decreased CO2 emissions, but also in reduced maintenance costs.

"There's a misconception that if you want to go green you have to spend more money, but that's not necessarily true," Akbarian says. "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 won't deteriorate as quickly."

This research was conducted as part of the Concrete Sustainability Hub at MIT, which is sponsored by the Portland Cement Association and the Ready Mixed Concrete Research & Education Foundation with the goal of improving the environmental footprint of that industry.

"This work is not about asphalt versus concrete," Ulm says. "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."

Denise Brehm | EurekAlert!
Further information:
http://www.mit.edu

More articles from Architecture and Construction:

nachricht Concrete from wood
05.07.2017 | Schweizerischer Nationalfonds SNF

nachricht Modular storage tank for tight spaces
16.03.2017 | FIZ Karlsruhe – Leibniz-Institut für Informationsinfrastruktur GmbH

All articles from Architecture and Construction >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>