So far the series hasn't established that though, that I can think of... The weird thing about the accident theory though, is a lot of the people dead in their cars are simplly sitting in a car, dead. No outward signs of trauma as it were, to neither the cars (in some cases) nor the people inside.
The random dead folks in the car does seem to be a bit of an enigma.
One theory I had though, considering this also appears to be not just an accident scene but a major traffic jam during a disaster/apocolyptic event, is that some of the occupants of the vehicles were killed by other motorists for what they had or wanted to take. Again, doesn't really jive with how som eof the people seemed to just die behind the wheel like they fell asleep or something till the car ran out of gas.
I find little things odd too but just chalk them up to mistakes like in movies and stuff. **** happens, and all that.