While it is perfectly natural for a doe to deliver a set of twins, it is dependent on abundant food sources in the area. If, for instance, a very dry year and little mast is produced in the wooded areas and farm crops suffer, the pregnant doe, pregnant with twins...one will win and absorb the other in the womb. Pure survival of the fittest and guarantee that one will have a better chance of making it on low nutrient supply from the mother, due to less than perfect feeding conditions for the mother. So, if you see a doe with one fawn, it does not necessarily mean she lost one due to being hit by a car DUmmies.
That said, here on our farm they are a huge nuisance. They wreak havoc on the crops. We manage to take our 2 a year for our freezer, and we let several people hunt the farm to help control the population. Still, there were 5 deer standing out in the area in front of the shop when I came in this evening.