This is Scientific American's 60-second Science, I'm Christopher Intagliata.
When you walk on a sandy beach, it takes more energy than striding down a sidewalk—because the weight of your body pushes into the sand. Turns out, the same thing is true for vehicles driving on roads.
"The weight of the vehicles creates a very shallow indentation or, you know, deflection in the pavement—and it makes it such that it's continuously driving up a very shallow hill."
Jeremy Gregory, a sustainability scientist at M.I.T. His team modeled how much energy could be saved—and greenhouse gases avoided—by simply hardening the nation's roads and highways.
And they found that stiffening 10 percent of the nation's roads every year could prevent 440 megatons of carbon dioxide equivalent emissions over the next five decades—enough to offset half a percent of projected transportation sector emissions over that time period.
To put those emissions savings into context—that amount is equivalent to how much CO2 you'd spare the planet by keeping a billion barrels of oil in the ground—or by growing seven billion trees—for a decade.
The results are in the Transportation Research Record.
As for how to stiffen roads? Gregory says you could mix small amounts of synthetic fibers or carbon nanotubes into paving materials. Or you could pave with cement-based concrete, which is stiffer than asphalt. (It's worth noting the research was funded in part by the Portland Cement Association.)
This system could also be a way to shave carbon emissions without some of the usual hurdles.
"Usually, when it comes to reducing emissions in the transportation sector, you're talking about changing policies related to vehicles and also driver behavior, which involves millions and millions of people—as opposed to changing the way we design and maintain our pavements. That's just on the order of thousands of people who are working in transportation agencies."
And when it comes to retrofitting our streets and highways—those agencies are where you might say the rubber meets the road.
Thanks for listening for Scientific American's 60-second Science. I'm Christopher Intagliata.