Hmmm.... domove might work for ya here... used in a script it'll tell an AI unit where to go without the need for bothersome waypoints
so... you might have to loop it so the AI is continually getting the position of the car being chased and attempting to move there...
just thinking now that it might be possible to set up a repeatable trigger like this:
Condition: car1 distance pigs > 12
On Activation: pigs domove car1
causing the pigs to move to car1 every time the distance between the two is greater than 12 meters.. ( you can of course fool with the distance to get the desired result and prevent accidents
)