Looks to me like the drive tires are there to disengage the train from the lift chain before it gets to the holding brake, and then using the green piece you see immediately after the tires to engage the holding brake "anti-rollback dog" so that the holding brake can do its job. Usually the green bumps are used, at least from coasters I've been on like Mantis and Bizarro, to lift the anti-rollback over the drive tires so that nothing gets caught or broken. This is especially helpful when maintenance has to back out the trains for the night. Griffon, Sheikra, and all the other Dive Machines have the same thing, although on those two you can actually get tours to see them up close.
In the simplest terms just think of it as the anti-rollback device flipped backwards once it hits the green piece.
EDIT: Here's a sexy picture to show what I'm talking about: