Type the following codes at any menu to activate the cheat:

RUSHHOUR heavy traffic
EMPIRE race on Empire City track
ELNINOR race with El Niņo car
MERC race with Mercedes
GOFAST enables super speed in Single Race mode
ALLCARS enables all cars, including Pursuit Vehicles

Type these codes right before you click the RACE button to drive the different nonplayer cars: 

GO01 Toyota Miata
GO02 Toyota Landcruiser
GO03 cargo truck
GO04 BMW 5 series
GO05 '71 Plymouth Barracuda
GO06 Ford pickup with camper shell

GO07 Jeep Cherokee
GO08 Ford full-size van
GO09 '64-'65 Mustang
GO10 '66 Chevy pickup
GO11 Range Rover
GO12 school bus

GO13 Caprice Classic taxi
GO14 Chevy cargo van
GO15 Volvo station wagon
GO16 sedan
GO17 Crown Victoria police car
GO18 Mitsubishi Eclipse police car

GO19 Grand Am police car
GO20 Range Rover police car/ranger vehicle
GO21 cargo truck (same as 03)