Use of Uber has contributed to a decrease in drunk driving accidents in some cities but not others, according to HealthDay.

Study author Christopher Morrison of the University of Pennsylvania said the availability of public transportation is one factor that may influence Uber’s effect on drunk driving. The findings appear in the American Journal of Epidemiology.

The study looked at car crash histories and Uber availability between 2013 and 2016 in Reno and Las Vegas, Nevada; Portland, Oregon; and San Antonio, Texas. Alcohol-involved crashes were reduced by about 60 percent in Portland, but not at all in Reno, the researchers found.

“The differences could be due to a wide range of different factors,” Morrison said. “One likely explanation is that local populations use public and private transport differently from city to city, and probably also use ride-sharing services differently from city to city.” He noted that Portland has many more public transportation options than Reno. People might choose to use these alternatives to private vehicles after drinking too much, he said.