Sometimes it’s the little things that matter. Sometimes they’re so little that they’re only 1/100 of a millimeter thick (about 0.0003 inches).
That’s the infinitesimally small indention your car makes in the pavement as it rolls on the road. From a microscopic perspective, asphalt is quite springy. That means that your wheels are effectively driving up a tiny hill with every rotation, like the effort of taking a footstep in beach sand.
The mundane sounding field of "pavement-vehicle interaction" is, well, mundane. But it does matter: a sizeable chunk of greenhouse emissions from wasted energy may be laid at the feet of old pavement that doesn’t hold its shape or surface as you drive over it.
A study by MIT civil engineers found stiffening the nation’s pavements could cut fuel use by 3%, the equivalent of 273 million barrels of crude oil, or $15 billion, per year. As a result, CO2 emissions (PDF) would fall by 46.5 million metric tons per year (more than Oregon emits from burning fossil fuels annually).
Even better, it’s free. Or, at least, the costs of improved pavements will pay for themselves over time, according Mehdi Akbarian and Franz-Josef Ulm of MIT, whose paper (PDF) on that subject will appear later this year in the Transportation Research Record.
"Better pavement design over a lifetime would save much more money in fuel costs than the initial cost of improvements," in a statement from MIT. "And the state departments of transportation would save money while reducing their environmental footprint over time, because the roads won’t deteriorate as quickly."
The study was backed by the MIT’s Concrete Sustainability Hub, an industry-finances research effort to reduce the materials’ environmental impact. As it happens, concrete tends to be a primary material for stiffer pavement. However, the researchers point out the study’ focus was to create the scientific foundation for greener infrastructure.
"This work is not about asphalt versus concrete," says Ulm. "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."