18-Wheeler: American Pro Trucker

Unlock Bonus Parking Levels
Finish each of the four parking levels to unlock a bonus parking level. Finish the bonus parking level to unlock a sixth parking level.
(Thanks to richie_starr@yahoo.com)

Unlock Bonus Trailers
Finish arcade mode with all four characters to unlock two bonus trailers in score attack mode, versus mode, and arcade mode (if the Nippon Maru is selected).
(Thanks to richie_starr@yahoo.com)

Unlock Lizard Tail
Beat the game with all of the trucks (including Nippon Maru).
(Thanks to richie_starr@yahoo.com)

Unlock Nippon Maru
Beat arcade mode with all four characters.
(Thanks to richie_starr@yahoo.com)