From the back of the box:
...And there they go! In the Crash Motor Melee, contestants maneuver around the course while avoiding the walls, other combatants, or their exhaust trails (which consist of potent chemicals that once burned will disable engines of vehicles which take in the fumes through their air intake system.) At the end of each round the smoke clears, vehicles are repaired, and the survivors who avoided the hazards successfully are awarded points. The first driver to reach enough points will be crowned Champion of the Crash Melee!
User summary:
Motor Crash Melee is played on a square grid. Each player controls a car on the grid. At the start of each round, each player selects a new direction for their car (ahead, left or right). Then, they draw a speed card that determines how many squares they move. Each car that crashes into the wall, another car or an exhaust trail is wrecked.