clipped from: www.livescience.com   

Age is a huge factor, too. A vehicle from 1985 emits almost 38 times more carbon monoxide than a 2001 model, on average.

The best and worst

BMWs did best. Hondas and Volvos also tended to pass exams more often than other makes, but were inconsistent from state to state.

Hyundai, Mitsubishi, Chrysler, and GM cars were the most likely to fail.

For trucks, Honda, Toyota, and Nissan performed best. Ford was a distant fourth. Chrysler and Mitsubishi failed most often.

Other findings
  • Poorly maintained vehicles were more likely to fail.
  • Increased fuel efficiency in both cars and trucks resulted in decreased failure rates.
  • Increases in miles driven resulted in increased failure rates.
  • The older the vehicle, the higher the likelihood of test failure due to increased engine and emissions equipment deterioration.
    • Automobiles emit fewer pollutants on average in spring and summer
    Foreign cars are not necessarily better