Successfully complete the indicated task to unlock the corresponding
vehicle:

Bus: Finish in first place in all Eliminator events. 
Dinosaur head monster truck: Participate in 250 simple races. 
Dump Truck: Get the "Overachiever" trophy. 
Monarch Mk I car: Get the "Ranked Streak" trophy. 
Nord Viking truck: Get the "Hero" trophy. 
Ozutsu Ronin rally car: Get the "Veteran" trophy. 
Wombat Mudslide ATV: Get the "Rookie" trophy.