I am pretty sure everyone gets frustrated when getting killed by a car that literally just touches him while it's moving. A car kill should be only possible when the car is moving over a specific speed limit, and the speed of the player getting hit by the car should be considered (Example: Say the cars are set to kill players while speeding over 15km/h. If a car is moving at 15km/h hits a player moving at 5km/h in the same direction, then the car shouldn't kill him, because it's only hitting him at the force of 10km/h).
Considering the kill speed of a car is 15km/h, what if a car hit a player while moving at a slower speed? Well, if it's close to the kill speed, let's say from 8km/h to 14km/h, it should knock the player off but not kill him immediately, and if the car was slower than 8km/h, it should just push the player. Now I may be asking for too much but while playing GTA IV, you will notice that pushing pedestrians with a car on low speed will make them 'ragdollialy' try to still vertical while they are being pushed, that would be amazing if it can be implemented in APB.
One last thing to point out. Pushing a player/ped with a car into a solid object (wall, car.. etc) should kill them without considering the speed.