Test Drive 4
To enter a cheat code, first go to the Save Game screen. Select Slot 10, type in the cheat code and press [ENTER]. You can
use multiple cheat codes together. IT IS VERY IMPORTANT THAT EVERYONE IN THE LAN GAME USES THE SAME
CHEAT CODES. IF PEOPLE IN THE LAN GAMES HAVE DIFFERENT CHEAT CODES ON THE GAME MAY CRASH
!!! 

Cheat codes

NOAICARS = No AI racers in the LAN game
STICKIER = No 3D collisions (you can still spin each other but your cars will not leave the ground)
AARDVARK = All collisions turned off
ITSLATE = No special effects (3Dfx version only)
CREDITZ = Show Credits with cool pics
SRACLLA = Unlock All Cars
LEVELLLA = Unlock All Tracks
SPAZZY = Test Drive on Acid
BANDW = Black & White Mode
MIKTROUT = BIG Cars
MPALMER = Mini Cars
GONZON = Fast Forward Mode
GONZOFF = FF Mode Off
BIRDVIEW = View From Above
NITROXXX = nitro boost with horn button
BOBCRED = extra credits
COLOUR = changes screen back to color when in b and W mode

These codes also work, but not quite sure the effect (possibly multiplayer only?): 

ASTIDERC
TSTIDERC
DSTIDERC
MASTER