When you walk on a sandy beach, it takes more energy than walking down a sidewalk, because the weight of your body pushes into the sand. It turns out that the same thing is true for vehicles driving on roads.
"The weight of the vehicles creates a very shallow indentation (凹陷) in the pavement, and it makes it such that it's continuously driving up a very shallow hill," said Jeremy Gregory, a scientist at MIT. He modeled with his teammates how much energy could be saved, and greenhouse gases avoided, by simply hardening the nation's roads and highways.
And they found that hardening 10 percent of the nation's roads every year could prevent emissions equal to 440 megatons of carbon dioxide over the next 5 decades—that amount is equal to how much CO2 you'd spare the planet by keeping a billion barrels of oil in the ground or by growing 7 billion trees for a decade. It reduces 0.5% of projected transportation emissions over that time period.
As for how to harden roads, Gregory says you could combine small amounts of certain fiber with high technology into paving materials. Or you could pave with specially-made concrete, which is harder than ordinary construction materials.
This system could also be a way to shave carbon emissions without some of the usual barriers. "Usually, when it comes to reducing emissions in the transportation department, 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 preserve our pavements. That's just on the order of thousands of people who are working in transportation agencies." And when it comes to improving our streets and highways, those agencies are where you might say the rubber meets the road.
