Car and hittest

1

I am making a game with a simple car driving, what i want is so when the car drives over the MC(grass) it will slow down to speed =2. The problem is, depending on which side its entering, it will either go in reverse or go faster. Say its speed -= 2 and it enters from the front, it will just bounce off, but if i enter from the back, it will speed up. Is there any way just to slow down the speed when on the grass? and another problem is that i need it to ignore the bound box of the grass. I will post the code later.