Given rough road's not finished, they'll reverse vehicle (4)

I believe the answer is:

cart

I'm a little stuck... Click here to teach me more about this clue!

'vehicle' is the definition.
(I know that cart is a type of land vehicle)

I can't explain the remainder of the clue.

(Other definitions for cart that I've seen before include "Heavy open wagon" , "Open wagon (to come after, not before, the horse)" , "Farm vehicle" , "Primitive transport" , "Something not to be put in front of the horse" .)

I've seen this clue in The Irish Times.

Want a hint initially instead of a full solution? Install my app