Not sure about road asphalt but for roofing asphalt anything heavy with citric acid works great.
Also asphalt is brittle and can be chipped off quite easy with a hammer if its real cold and this will not leave any residue. I would definatly try beating on it before soaking ay solvents into it.
Id stay away from heat period. If youve got clean metal itll end up sticking to it more so while dirty rusty metal will help with breaking up the adhesion.
Jeff
