Johannesburg is the carjacking capital of the world. I worked in Johannesburg and often drove a car at night, doing shifts. I was always armed.
The carjackings became so frequent that many hospital staff members were taking specialized 'anti-hijacking' courses (that's what they call it in SA, hijacking). The perpetrators are called hijackers, but I call them goblins.
I completed one of those courses in 2002. They had a vehicle on the range, and we fired from inside the car and from outside. This was done with a driver only and also with a passenger.
Here is what I found:
1) As another poster said, it is better not to stop somewhere where you can be surprised, boxed in or made to drive the vehicle where it is in a vulnerable position. This means you need good following distances, you are better off in an outside lane, and it is good practice to 'time' the traffic lights so that you catch them green.
2) A goblin can approach the car in the driver's blindspot. By the time the driver sees the goblin, it is too late and the goblin has the drop on the driver. The cure for this is to get one of those small blindspot mirrors and place that on the lower inside corner of the side mirror.
Check all of your mirrors frequently!
3) Whether you are wearing a seat belt or not, it is very difficult to draw quickly from an IWB holster (that's the only one I personally tried). Another trainee found it difficult to draw from an OWB holster. Any draw that has a rearward elbow movement can be impeded by the car seat.
4) If you're going to draw, you either have to do it very early in the encounter (before he gets the drop on you) or very late (as you are getting out the car or unclipping the seat belt). If you think you can out draw the goblin who is already at the driver's side window and has the drop on you, think again. If he is at the window already, and he has his gun drawn, you are in big trouble. You will be better off gunning the engine than trying to draw and pop the goblin.
5) If the goblin is experienced (and you have to assume that he is), then if you make any move whilst in the vehicle that doesn't fit in with a dude trying to take off his seat belt and get out of the car, you are going to get shot. In South Africa that means any kind of reach on the right hip, since the driver sits on the right and his seat belt release is on the left hip side. You have no business reaching low right, low centre or high left. The only logical place therefore (according to my experiments) to have the gun is low left.
6) I found that the best method of securing the gun was under my left thigh. yep, almost sitting on it. Only the grip is exposed on the left. If the goblin looks sharp and he has the drop on you, you might actually decide to ditch the gun between the seat and the centre console as you undo the seat belt and move to get out. You've still got the option to draw it after you release the seat belt, but I guess it would depend on whether you thought you could win or not.
7) In South Africa, I am resigned to left hand draw and fire and I practised that on the range, from within a vehicle. It wasn't my vehicle. The only practice I had in my vehicle was drawing and pointing. On one occasion I drew for real but didn't let the pedestrian see the pistol.
8) I found that the first time I fired from inside the car, with a passenger who was also firing (left hand seat, right side ejection port) I was distracted by brass landing on the roof and rolling down the windscreen.
9) If the goblin hasn't drawn level with the driver's side window yet, you can move pretty quickly and get out and shoot if you can't move the car. This is the sort of scenario where you have come home, the car is parked in the driveway and then the goblin makes his move.
10) in SA many hijackings happen when pulling out of the driveway or stopping at the gate when coming home. Many homeowners cut down hedges and bushes near the gate, or made sure they had an electric opener and didn't have to stop at all. There is a lot to be said for having good visibility of your yard, and of course good lighting in your driveway and outside your house on the street. Remember, goblins are like roaches and prefer to do their dirty deeds in the dark.
11) If you are really extreme, you can get a Blaster-type system, but I think in many places you will get into trouble for cooking someone like that, even if he is a goblin with a gun at your window.
If you take a car on the range and go through some scenarios, then take my advice:
a) Expect massive bruising on the underside of your right thigh (if it is a right hand drive vehicle) if you do a lot scenarios where you have to get out of the car in a hurry. When we were finished that course, we all had massive bruises and the pain was pretty good the next day.
b) Do not be tempted to rest your bare forearms between the windshield frame and the door frame when the vehicle is stopped and the door is open, and you are firing a Ruger Super Redhawk. That rubber on the windshield and door seal may look soft and feel soft at first, but it can cause serious scratches