Okay, but this causes something that looks kinda like what i call "the Gran Turismo effect", because you're speeding at 300km/h (miles?) and all of a sudden your car comes to a complete stop without a scratch, let alone a dent, heck, even your paint is still intact!
If you want to do something like that effect, try giving a slight logical reaction such as a broken hood, engine, fuel leak, a broken window or such.This would also give the whole "lifestyle" term a new breath, seeing as you could then go to a mechanic and have your carglass repaired, engine fixed, or what ever just broke...
On the other hand most of us wouldn't want/like it if you can't turn it on/off, beacuse this would lead to more law-abiding driving, so never mind that... All i'm saying is it should be slightly realistic, just even by making the cars move a bit, and have you arrested immediately after you broke it (the roadblock).You could also make the cars fly away into space for comical effect, but just have you arrested immediatly after that.
(If you really took the time to read all of this, i salute you :D )