hey all.
Can somebody explain how the collision detection works for race tracks in games like need for speed or wipeout?

Thanks.

I don't know personally what collision systems those particular games use. However, there are several physics/collision engines available (Ogre, Bullet, ODE, etc.) which have been used for commercial games. Many of the websites for those engines "advertise" which games they've been used for. You may want to take a look at those pages.

In general, each graphical component (walls, cars, etc.) has a collision object/shape associated with it. Each frame, collision detection is performed, looking for objects which intersect. Information on each collision is stored and, following the collision detection phase, that information is passed to the physics engine which determines how each object responds to the forces on it that frame.

The corresponding graphical component for each object is then drawn appropriately for its new position/rotation.