Kramer and Newman hatch a scheme to arbitrage bottles from NY, where the deposit is 5 cents, to Michigan, where the deposit is 10 cents. They can't figure out how to make the costs work; gas is too expensive (variable costs), and there's too much overhead (fixed costs of tolls, permits, etc.) with using a semi to haul the bottles in volume. Finally, they hatch a scheme to use a mail truck, which lowers their variable and fixed costs to zero.
The German truck lightly taps the back of a Ford Pinto, and it explodes. This clip illustrates the poor design of the Ford Pinto vehicle. Ford Motor Company chose not to fix the Pinto's flaws because it was cheaper to pay for the cost of settlements for deaths, injuries, and vehicle burnouts.