The Cash for Clunkers Program offers you a of $3500 rebate if you trade in a car that gets at most 18 miles per gallon, and purchase a car that gets at least 22 miles per gallon (and of course you can’t just use your rebate to buy a 5 year supply of metro cards, because I guess that would save too much gas). 22 MPGs strikes many as a pretty meager milage requirement (because it is), which is probably why the program offers an additional $1000 if your newly purchased vehicle increases your fuel milage by 10 MPGs (although both rebate conditions are less strict for SUVs and trucks).

Encouragingly, preliminary reports seem to indicate that the majority of trade-ins are meeting the 10 MPG requirement. Still, one can’t help but wonder if a minimum fuel requirement closer to 30 MPGs would make the prograe more worthwhile (particularly since today’s new cars are required, on average, to get 27.5 MPGs, and this number will increase to 30 in 2011). Perhaps it would, but the current situation isn’t as dire as you might think.

Consider the following example:

You trade in a car that gets 17 miles per gallon. That’s quite close to .59 gallons per 10 miles. You switch to a 24 mile per gallon vehicle, which is a bit under .42 gallons per 10 miles. Assuming you drive 1200 miles per month, and don’t change your driving habits, you’ve saved over .17 x 1250 = 20.4 gallons of gas. Now suppose you wanted to save an additional 20 gallons of gas, you’d need to go all the way to 40 miles per gallon. At that point you’d be down to 30 gallons of gas a month, and saving the next 20 gallons would require that your car’s milage enter into hypothetical chevy volt territory.

Of course the above example isn’t completely honest. People do drive about 1200 miles per month, but people also change their driving habits based on their car’s fuel consumption. My intuition is that this only leads to a modest reduction in fuel savings (particularly when gas is expensive), but it’d be interesting to see some real numbers.

Incidentally, in Europe, where conservation is all the rage, they already do the whole gallons per mile thing (except they call it liters per kilometer, which is sooooo like them). In contrast, miles per gallon strikes me as a reflection of this country’s love affair with the open road. Here in the states, when we’re looking to buy a car, we want to fill that bad boy up with a tank of gas and drive as far away as humanly possible. In Europe I’m pretty sure they just all sit around by fountains or something.

If we assume that each month I drive 1000 miles (although my real total is much closer to zero), then a 27 mpg car (the current standard) requires 37 gallons of gas each month. A 37 mpg car, meanwhile, requires 27 gallons of gas, and a super efficient 57 mpg car requires about 17.5 gallons. Going from 37 mpg to 27 mpg saves about as much fuel as going from 37 mpg to 57 mpg, and from there going to 80 mpg only saves 5 gallons more.

Earlier this month my housemate and I were a little disappointed with the recent (and long overdue) 10 mpg increase in fuel efficiency standards (by 2020). Now I feel a bit better about the whole thing (although the EPA’s decision to block individual states from raising standards further is still ridiculous).