cars pass through other cars

Hey Experts,
I need help! I want to collide cars with each other in free roam. So i fallow fallowing steps.
1) Once free roam started i loaded another car few distance from starting point & both cars are facing with each other.
2) I am using AI script manager & runs cars one by one and record the path.
3) When I play recording and when cars cuts each other path they just pass through each other but no collision at all.
So am i doing anything wrong? or I need change any settings?
please guide me, thanks in advance.

 

If you go the Settings, Gameplay & scroll down a bit, is the 'Simplified Collision Physics' option checked? If yes, uncheck it & that should solve the problem