We have just about completed the transfer to Verlet-based physics. We had car-car collisions working already but now we also generate verlet walls to keep the cars on track. It was relatively simple too- most of the wall code we had already was directly applicable to verlet. The only real problem was that tracks that were too long would cause out of bounds errors when creating all of the walls. Predicting when those cases would occur and generating a new, hopefully shorter, track fixed that up and has the happy side effect of limiting how long tracks end up being.
Fine tuning controls and balance as well as importing all of our various assets will be the entertainment for the coming days.
As far as me goes, I have thinking game design for the last few days non-stop. Any extra processing time my brain can find has been redirected from its regularly-scheduled recital of Lady Gaga lyrics to mulling over game design ideas and decisions. The challenge now is to find time to code all these ideas, which means learning how to efficiently prototype. Which will be a valuable thing to know!