In every level, there is 1 hidden car somewhere on the map. And these are the locations.

Item	Location
4-Wheeler -Level 4-	In the trailer park, between 2 trailers
Boatmobile -Level 3-	Squidport, On the C.SPANKER, where the stacked boxes are, climb the boxes and will be on the other side of the green cargo crate
Obliterator -Level 5-	At the stadium, Replaces the fountain
Pink Cadillac -Level 6-	Planet Hype roof, crashed on the wall below you
RC -Level 7-	On The Roof of the Krustu burger
Rocket Car -Level 1-	Parked on the driveway of the Golden house on the rich side of Springfield
The Monorail -Level 2-	In Downtown after the stadium tunnel, before the highway, go to the Monorail Station and it will be on the ruins or the tracks.