E,

Because more people prefer driving at night.

"Many drivers who avoid driving at night no longer did so."

D doesn't explain the reason of the increase.

E.

D explains the category of accidents but not the increase in accidents
E says that before the markings were painted, many ppl have avoided driving at night but after marking were painted these ppl have started driving at night. So due to painting of the markings, many ppl have started driving and hence increase in accidents.

I feel the answer will be E