So today I am doing something completely different I've done so far - the physics system. It is the next big challenge aside from the track coordinates and AI.
For collision detection and simpler stuff I will be relying on Blender's Bullet Physics system, but more advanced things - track space constraints, hover spring-damper system, vehicle handling and behaviors I will have to write from a scratch. And as an artist I am very good at it :P. Fortunately we have an Internet and there are a lot of really helpful resources for this.
The first thing I tried to implement was a mass-spring-damper system. I will be using it to make the vehicles levitate above the ground/racetrack surface. The idea is to cast a ray from the vehicle's vertical axis down. If it collides with a surface the spring-damper simulation will run and apply the calculated force to the vehicle.
The most helpful resource I found had an actual Blender Game Engine implementation already :). HERE is the link where I found it. It is done by Sebastian Korczak, same guy who is making the Burster - a web browser plugin to allow publish and play Blender files online. I will be using it at one point of development to show off the progress.
So after some changes I had a nice springy levitating box.
Another thing I managed to create - a force field that will keep the race car close to speedway's surface, thus preventing the vehicle to fall off the track surface even if the speedway is oriented upside down.
blend file HERE