The title is the question.
Maybe it’s the cheapest thing with the right properties, but can’t it be painted with something a little more reflective, that won’t absorbe so much heat from the sun?
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Another reason–concrete does not need to be resurfaced regularly so the politicians can’t get regular kick-backs/donations from the road builders.
It’s cheap, highly available, easy to install, cures quickly, produces very little running noise, and can be removed easily for the next replacement.
Unfortunately, it wears and settles as an absurdly slow-moving liquid when subjected to extreme pressure, like say under the tires of a truck or bus, and it retains heat due to its chemical properties and low albedo (absorbs more light than it reflects, hence it retains the heat energy).
It’s a tradeoff that needs careful consideration, but the pros often outweigh the cons.
San Antonio TX is implementing this actually! They started with a pilot program where they tested multiple road materials and coatings. It is now rolling out to the city at large. It’s supposed to cool the area by 20 degrees farenheit.
It works, and it’s cheap. There really isn’t a reason to paint it, because it doesn’t really matter that the road is hot. Car tires are pretty heat resistant.
Why would you want your road to be reflective? That sounds very dangerous, not to mention it would be baking anything on top of it.
To combat the heat, they should plant more shade trees along the side of the road. This is a win-win for everyone.
Nobody has mentioned that asphalt is wildly good at maintaining traction for car tires. It’s even better than concrete in a lot of situations. Painting it makes it less so.
In addition to the other answers, tire marks. And every other type of stain. If you had white roads or yellow or any other color it would be hard to paint them to contrast, and they’d get marked up and scuffed from tires and you’d see all the oil that’s dripping out of everyone’s car all the time and whatever other fluid they’re leaking or dumping out the window
Alternatives have been tried but almost always end up being too costly to be considered widely applicable. Look up solar roadways. They launched in 2006 and didn’t get their first road equipped until 2016. It’s a good idea but who’s gonna fund it?
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