What’s the deal with the bus stops paved in concrete? I mean, why not just pave the suckers in asphalt like the rest of the road?

D.C. bus stops’ concrete slabs bear the burden of the daily stream of buses better than asphalt, says District Department of Transportation (DDOT) spokesman Bill Rice. If DDOT used asphalt rather than concrete for the 10-by-60-foot rectangles, Rice says, the asphalt would shift and create waves or ripples under the buses’ weight. And when asphalt shifts, it cracks and can create potholes.

Moreover, compared to asphalt, concrete is stronger, longer-lasting, and reflective at night—which helps distinguish the bus stops.

Bus stops that don’t have concrete rectangles are often a result of utility workers who tear up the road to do their work and then they pave over the slab in asphalt. In other instances, DDOT hasn’t yet caught up to a changed bus route.

But if concrete is so much better at handling use and weight, why not pave all the District’s roads in concrete? That’s because concrete is far more difficult to repair, Rice says.

Civil engineers call asphalt a flexible pavement. As such, asphalt roads generally consist of a thin layer spread over a gravel or stone base and sub-base. The layers rest over compressed soil. When a large weight—like a bus—rests on the asphalt, the gravel or stone base shifts.

In contrast, concrete surfaces may or may not have a base course between the pavement and subgrade. When a large weight rests on concrete, the weight is distributed over a relatively wide area of the subgrade. However, since concrete’s surface is thicker than asphalt, repairing concrete requires replacing the entire road, whereas repairing asphalt requires only scraping off the top surface and relaying a new surface.

And beyond the surfaces’ abilities to bear weight, asphalt provides for a smoother ride, Rice says.

Every Monday, the ‘Huh?’ Bub takes your questions. Got one?