You're going to have to give more information to get a complete answer. Please explain how he hit you in the west bound lane if you backed into the east bound lane? Did you have to cross the west bound lane to enter the east bound lane? Were there any skid marks and were they measured and documented on a police report? Does the damage on the vehicles indicate a high speed collision?
When determining liability you have to start somewhere. You always start with who has the right-of-way and in this case the other car does. Now if it can be proven that the other car was indeed speeding, then that is a contributing factor. But, it does not relieve you of the responsibility of using due care. Unfortunately for you unless the witnesses were cops with radar guns or a baseball scout with a "jugs" gun it's tougher to prove speed as a factor.
With out knowing the answers to all the questions, right now you have most if not all the liability.