Wave the Flag:
At the title screen hold R1, R2, L1, and L2 and move the flag with the d-pad and the buttons.
Beat the Time Trial Bonus Track to get the black car.
Beat the arcade game at the loading screen and you will get a whole new selection of cars.
Right after the race has started, turn around and drive straight into the brick wall. There will be a sign on the top of your screen that says wrong way but ignore it, and keep driving straight into the wall. Then it will take you into the first tunnel except it will be a mirror version of the entire track.
Thanks to Revolution readers Austin Carter, Nick Altieri, Bill Shirer, Ryan, and Steve Read!