Race any track on legend or veteran in the quick race mode and any track you race at, and if you win, you will unlock a new hidden track. The bonus tracks that you will unlock are the tracks behind the normal tracks that say locked, such as the Alabama 500 at Talledega, that is the night race. For example if you win Taledega you unlock the Alabama 500. This goes with every other track except Indianapolis speedway, New Hampshire and Bristol. These tracks do not have hidden tracks.