Presumably it just depends on whether the road is congestion. Roads are essentially non-rivalrous (my use of the road doesn't reduce your ability to use the roa

Presumably it just depends on whether the road is congestion. Roads are essentially non-rivalrous (my use of the road doesn't reduce your ability to use the road), until the road is congested. Presumably most congested roads are used mostly by cars, so I suppose you could say that "cars cause congestion and congestion makes buses slower." But of course, the congestion also makes the cars slower as well.