Mindbleach, thanks for the great suggestion. I tested out variable tile speeds today and I think a time trial is the way to go to make it a proper game. Plus I can focus on focus on polishing the core driving mechanics, like collision/sliding. After staring at the "graphics" part for so long working on game mechanics will be a relief :)
Without more tracks you can still go forward or backward
I never thought about reflecting or reversing the track lookup table. That should be straightforward to try!