Thanks to their bright yellow paint job, black stripes, and built-in stop signs, school buses are some of the most immediately recognizable vehicles on the road. A lot of them also have white tops—which, like other aesthetic elements of the buses’ design, serve a purpose.
As AccuWeather reports, that purpose is mainly to keep the interiors cool on hot days. This might seem self-evident to anyone who knows not to wear black or stand barefoot on asphalt during a blistering summer afternoon. Darker colors absorb more light, which then gets converted into heat. While school bus yellow may not exactly seem like a dark color by itself, it’s comparatively darker—and therefore faster to heat up in the sun—than white, which reflects almost all light.
Back in 1992, The New York Times reported on a study in North Carolina that found that school buses with white tops were roughly 10 degrees cooler inside on summer days than those with yellow tops. During the hottest hours, the contrast could rise to 17 degrees. Another upside of the white tops, as one assistant superintendent told The New York Times, was that other drivers had an easier time spotting school buses on the road. So the state started letting schools choose white roofs over yellow ones—a trend that was also already catching on in California, Florida, and Georgia.
The white tops didn’t just make the kids more comfortable during their commute; their behavior also apparently improved, too. “It seems like the kids are a lot calmer,” one bus driver told The New York Times.
Since a lot of school buses are air-conditioned these days, white roofs might not seem quite as crucial as they once did. But they do help make the A/C system’s job easier. And school buses aren’t the only vehicles to adopt the white-on-top custom: Some UPS trucks—not all of which are air-conditioned—feature white roofs, too. It’s not their only tactic for keeping things cool.
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