MNN - Mother Nature Network

For most Americans, the word clunker triggers a memory from summer 2009: the CARS (car allowance rebate system) program, commonly referred to as "cash for clunkers." The government offered up to $4,500 to each person who traded in a qualifying clunker — a vehicle reaching less than 18 mpg. An overwhelming 85 percent of vehicles traded in were trucks (and 59 percent of new purchases were cars). 670,000 autos and $3 billion later, the roads are a much "cleaner" place; fuel efficiency has improved by an incredible 58 percent. Check out the top 10 clunkiest clunkers here.