Driving around isn't going to give you enough of an idea of their numbers. You need to stake out in a field around 6:00 pm or thereabouts and watch for them flying over.
Went out yesterday from noon to 1:30. Not the time I prefer to be out dove hunting but I had to work last night so better than not going at all. No doves spotted though, which I had expected. I prefer hunting them from about 4:30 until dusk. Thats when I normally see the most birds.