I don't understand How C explains the paradox

@cynthia-lee your prediction of people avoiding the road during the rush hour would be a perfectly reasonable explanation, however it is not an answer choice. (C) is correct because it gives us an explanation of how lowering a speed limit could lead to faster travel times. It says that prior to the reduction, there were many high-speed crashes that caused long delays. The reduction in the speed limit reduces these high speed crashes, and thus reduces long delays. So even if the speed limit is lower, the reduction in delays can more than make up for the lower speeds. I hope that helps!

Got it, thanks