I had my limbs crack on me about 4 years ago. I really didn't know any better and left my bow in the truck all day and it was hot. I was taking my bow to the shop after work that day to have them give it a once over like I always do and they noticed the cracked limb. Thank god I didn't pull it back. I don't think that having a bow in the car while your driving will do any damage. It's like others have said....leaving it in your car or trunk while the windows are rolled up.

I delaminated both limbs on a Mathews Ultra Max in 98' because I was a knucklehead
It was about a 90+ degree day and I put my cased bow (black case) in the bed of my truck with a black bedliner.
Even at highway speeds, 2hrs later the limbs were toast.

Lesson learned.

Year ago I ruined a bow by leaving it in the back of my jeep one day, all day, during August. I didn't know any better....