Not only do you have to deal with slightly higher voltages, but you'll also have to deal with fluctuations in voltages, as well as potential spikes; granted, these will likely be smaller at the rear of the auto vs the front (well, assuming your engine is at the front of the vehicle). You might want to read the following Atmel app notes for such applications:
http://www.atmel.com/Images/doc9108.pdf (*)
The one app note marked (*) is done so because Atmel noted it as "mature" and "not recommended for new designs"; it is probably still worth a look - I don't know about the other two, but you might want to review Atmel's documentation section - they have a lot of good stuff in there that may help you on your project.