Before eyeing your next car purchase, be certain that the vehicle you're thinking about trading in qualifies under the Car Allowance Rebate System (CARS) program. Some popular older vehicles such as the 2000 Dodge Minivan or 2000 Ford Taurus don't qualify because they officially get more than 18 miles per gallon. Also, the Department of Transportation uses only the officially listed estimates of combined city and highway fuel mileage, and these estimates were recently revised, meaning cars that once qualified may not now. Other guidelines on clunkers: the car cannot be more than 25 years old, must be in working condition and must have been manufactured no later than the 2001 model year. Finally, to qualify under CARS, the vehicle must have been registered and insured over the previous 12 months. To verify qualification go to www.cars.gov.