To unlock levels in Road Trip, go to the Press Start screen and enter the codes listed below to unlock the corresponding levels:

Las Vegas: Y, R-Trigger, L, L-Trigger, Right, Y
LA: Y, Left, B, B, Left, Y
Chicago: Y, Up, B, Up, B, Y
New Orleans: Y, Down, Right, Up, Left, Y
Portland: Y, A, A, B, B, Y
Boston: Y, Up, Down, Down, Up, Y