A new study shows 57 percent of fatal car crashes involve a driver who tested positive for alcohol or drugs. Alcohol was the most common substance detected, followed by marijuana and stimulants, Reuters reports.

One in five of the 20,150 fatally injured drivers between 2005 and 2009 had multiple substances in their system at the time of the accident. Men and people driving at night were the most likely to have used alcohol or drugs, according to the study.

Study co-author Joanne Brady of Columbia University in New York told Reuters that not all states test for the same drugs at the time of a crash, or have a policy to test consistently at all. She added it is not definitely known how multiple substances might interact to affect a driver’s ability to focus on the road.

The findings appear in the journal Addiction.