Yes, that's why I said, that it only makes sense against other cars
It is just a start, you would have to further split the events by adding sub-events, to catch all possible situations, e.g.
+ car's speed is negative
-> set a variable to -1
-> set a variable to 1
+ on bounce
++ colliding with another car
--> Set speed as mentioned
+++ variable is -1
---> do what is needed if the car hits anything but a car, while driving backward
---> do what is needed if the car hits anything but a car, while driving forward
It should be doable. But, of course, you can always try to do it with custom behavior. It's just, that you don't need to completely redo the car behavior, just those on bounce situations, and therefore events are the easier solution with less overhead.