# Cash for clunkers and the unfortunate math of MPG

Pop quiz: Which is a better deal for the government? Replacing a 10 MPG truck with a 12 MPG truck under the cash for clunkers program or replacing a 24 MPG with a 36 MPG car?

The correct answer is of course replacing the truck.

Consider both of those vehicles driving 120 miles.

The truck goes from using 12 gallons of fuel to 10 gallons of fuel, saving 2 gallons.

The car goes from using 5 gallons of fuel to using 3 1/3 gallons of fuel, saving 1 2/3 gallons of fuel.

It’s an unfortunate byproduct of Americans measuring the inverse of fuel efficiency. Europe and Australia don’t have this problem because they use L/100km.

For example: Which is a better deal for the government? Replacing a 10 L/100km MPG truck with a 8.33L/100km truck under the cash for clunkers program or replacing a 4.16 L/100km with a 2.77 L/100km car?

In this case, all that is required is simple subtraction to see that the truck nets you a 1.66 L/100km gain while the car nets you a 1.39 L/100km gain.