In the Freeway level (not the Highway loop) grab a few fire missiles and head off to the construction yard you should see two cranes. One to the left and one to the right your target is the one to the right. You will see a Control cage hanging in the middle of the crane all you need to do is hit this once with a missile. The best way to do this is angle yourself driving at the hill with a straight line between you and the Control Cage. Hit a turbo and launch off the hill. While in the air launch a missile. If done correctly the missile will hit the cage and cause the crane to lower a box. Drive over to the box and shoot it until it opens and gives you Axel. This one may take a few tries to get it is the most difficult character to unlock.