Get the distance

[kefeihappy]

Hello sir ,  I have a question need  your help!
It's a Car's Game, The road is a Model of 3ds,
the car in the road,I want to get the Distance to the road on both sides of the car， 

to Make the car in the road!  ( both sides of road  is  wall!)

can you help me !
Thanks you!(Please forgive my English is not good, I'm from China)