Related quandary - do you record audio too?
B/c that means that any conversation occurring in the car is at least potentially recorded.
This can also be seen as an invasion of privacy by any passengers. Or, even if you use your car stereo for a hands-free phone call.
Depending what state you happen to be in at the time, that may be a felony.
My take on it is this - the best setup is something that auto-deletes unless specifically told not to. Then you will only have access to something for which there was an explicit reason at the time, and you can then make the personal call if keeping/letting it be known that you have said recording based on the circumstances.
E.g. might want to give up on that video of a crazy vehicle you passed while talking to your girlfriend about when your wife was leaving town