To beat Smithers to Mr. Burns in the last mission in level 1, purchase the Duff Truck from Gil and use it in the race. Immediately when the level starts, drive it so it is facing the entrance booth and stop it halfway between the fence and the booth. Immediately exit from the car. Borrow a car that is driving into or out of the plant to drive to Mr. Burns while Smithers keeps trying to get the truck out of the way. If done correctly, he will not be able to do so.

Enable the "One hit traffic death" code. As soon as the race starts, drive into Mr. Smithers. He will explode, and you can then just drive to Mr. Burns.