[Mobhack]

Reversing takes 3 times the cost of that hex in forwards motion, not 1/3 of the units MP.

So - 3 MP on a road usually, 6 on clear terrain with a tracked vehicle typically, per reversed hex.

Stick chance (in a swamp say) is increased as well - by 25% I think it was. Reversing into poor going is not a good idea if you can avoid it.