Green

Want to cut heat in the city? Paint the roads white

BMW's DriveNow is still relatively unknown in the San Francisco area
Image Credit: BMW

It’s fair to say we don’t give roads much thought unless they’re doing something wrong.

You certainly notice them when you run over a pothole, for example. But what about when they’re radiating heat on a hot summer’s day?

The effect of all those roads is estimated to increase city center temperatures by as much as 12 degress Fahrenheit. Could lighter roads be the answer?

It’s a question being asked by the Cool Change Cities Project (Renew Economy). As much as 24 to 35 percent of a city area is dedicated to roadways, and they’re typically paved with asphalt.

This dark surface absorbs the daytime heat, radiating it out again all day and into the night and raising overall temperatures. Combined with buildings and other human-made spaces, it contributes to the “heat island effect”, where urban areas are significantly warmer than rural land.

That, in turn, increases energy use. An extra 12 degrees of heat on a summer’s day means an extra 12 degrees of cooling to bring a building or car interior down to a comfortable temperature.

Painting building roofs white has already worked to great effect in tests, reducing the amount of energy a building uses to keep cool. The lighter exterior reflects heat better than a typical dark roof.

There was even a rumor several years back that the sale of black cars would be banned in California, based on similar thinking — though this did turn out to be just a rumor.

Roads wouldn’t need to be painted white, exactly — though doing so would reflect significantly more heat than existing surfaces.

Instead, using a pale resin in their construction or lighter aggregate particles to produce a lighter road surface would go some way to reflecting rather than absorbing daytime heat.

There are issues with this, to a degree. A fairly light surface could result in a lot of glare from the sun, particularly at higher latitudes during the winter, when road glare can be an issue even on dark asphalt.

It would also require roads to be dug up and replaced, which costs money and uses huge resources.

Still, it could save resources too. According to the Cool Change Cities Project’s leader, Michael Mobbs, one recent example of a road repaved in a pale surface cost $58 million, versus $57 million in energy savings.

And roads need repaving anyway — why not make them lighter when the time comes?

This story originally appeared on Green Car Reports.