I'm sure all of the driving was automated... they created a liquid texture thing, like the squids in the matrix... a group of solids that behave and flow like a liquid.

then they "dumped" the cars down through the map and let things fall as they may.

It's crap that the cars are allowed to clip through each other but not the buildings and ramps, and that they always land on their wheels to keep going down the hill.

Looks like a senior project for CGI school, not a polished piece of art.