While opening a car door, drivers check if any vehicles are behind.?
That is a pretty common sense question you are asking. You are actually entering a lane of traffic flow (my answer is for the USA, as you didnt stipulate what country you are talking about) and are a pedestrian and therefore responsible for using care so as not to cause an accident. In Calif. this could be considered jay walking if you were the cause of an accident while trying to enter a vehicle while traffic is flowing in the lane of the vehicle for which you are attempting to enter on the drivers side of the vehicle. That amongst other reasons is why I have a dash cam to prove what happened should an unfortunate incident like that were to happen to me. So in answer to your question, yes the same thing is applicable when entering the car. You may want to consider enrolling in a drivers safety course.