Brake fade typically occurs during heavy or sustained braking. Many high-speed vehicles use disc brakes, and many European heavy vehicles use disc brakes. Many U.S. and third-world heavy vehicles use drum brakes due to their lower purchase price. On heavy vehicles, air drag is often small compared to the weight, so the brakes dissipate proportionally more energy than on a typical car or motorcycle. Thus, heavy vehicles often need to use engine compression braking, and slow down so braking energy is dissipated over a longer interval. Recent studies have been performed in the United States to test the stopping distances of both drum brakes and disc brakes using a North American Standard called FMVSS-121. The results showed that when newer compounding of friction materials typically used in disc brakes is applied to drum brakes that there is virtually no difference in stopping distance or brake fade. As the United States changed its FMVSS-121 rules for Class Eight trucks built in 2012 to reduce stopping distances by about 1/3rd there was no recommendation to use either drum or disc brakes in the current law.