I realize you are talking about in reality about shooting at vehicles but this came to mind.
Actually this very circumstance is used in teaching cops and others in the use of force.
A car is coming towards you with the intention of causing bodily harm. There is nowhere to go. You draw your weapon and fire into the windshield killing the driver. This would be a justified act of self defense.
Same car coming at you with the intention of causing you bodily harm. This time just as he gets to close you jump to safety. As the car passes you fire into the back window killing the driver. This is not a justified act of self defense. The direct, immediate threat is gone. It does not matter what he coulda, woulda done. If he goes down the street and turns around to come back the scenario starts all over again.
In regards to shooting at vehicles. Windshields can be tougher than they look, standing in front of a car speeding toward you while taking aim for a shot on the driver's head is harder than it looks on TV, and if you are lucky and hit the driver now you have to deal with a speeding car headed towards you with no one controlling it, now what?
As stated move laterally or opposite to the cars direction. Get behind something if possible. If you have to take the shot not much else to do.