No, what I meant was make sure the camera is locked off while shooting the greenscreen footage!
The camera in the car can move about no problem as the the guy getting run over will be tracked on to a point on the road, which reminds me, you might want to put a marker down on the road where the guy gets run over, just behind where you want him to be, then you won’t have to paint it out after. This will give you a location marker in the 3D track as well if you were to track that way.
The problem if you use a point track might be when the marker disappears under the bonnet when you get close in, you would then have to track something else in the seen and link them together. A 3d track would be a better option in my mind, as long as there was enough scenery in view outside the car to get a good track. Hope this helps.