Back to vehicles.
Sometimes your car may be the only source of cover you have available, but to use it you have to know a few basic things. By and large, most cars are constructed of thin layers of metal, fiberglass and glass; none of which are well known for stopping bullets. Hiding behind your car door is not going to be a safe spot unless it has been armored.
If you have to engage a target immediately from the drivers seat, you can open the door and use the “A post” to provide you with a modicum of protection, but this is a “best you can do in the situation” firing position. It does give you the advantage of remaining behind the wheel so that you can drive away. You can see Clint Smith doing this in the following video:
On average, the best areas of cover behind a vehicle are the engine block and the axles. The block is the largest area of solid metal available, but the tires, rims, brake components and the axle itself will stop many projectiles. The advantage of the front end of the car is that you don’t have to make yourself “as small” as you would need to make yourself to hide behind the rear axle.
Another thing to remember about vehicles is that rounds can travel under them, either through direct fire or via ricochet. This can be used by your opponent or yourself.
As a LEO, something I try to do as I approach a location is estimate where the threat is most likely to be. What I want to try to avoid is pulling up so that the suspect/subject is on the drivers side of my vehicle. If I do that, I will be exiting the car directly into a possible line of fire. My only other options would be to drive off under fire or crawl across the seats and out the passenger side door. Wearing all the gear I do and considering all the equipment inside a squad car, that is not a tactic that places high on my list of options.
Therefore, what I try to do is pull up to location so that I can exit the vehicle and immediately use the engine block for cover if necessary.