It’s a tempting assertion for Uber to make: the easier it is to hail a ride home after a night out, the less likely people will be to drink and drive. Uber claims as such on it’s website. “Services like Uber—where passengers push a button and get a ride in minutes—are helping to curb drunk driving.” For the last three years, the ride-hail service has been partnering with Mothers Against Drunk Driving to promote efforts to curb drunk driving.

Uber’s impact on drunk driving statistics across the US is unevenly felt

But Uber’s impact on drunk driving statistics across the US is unevenly felt, according to a new study. Researchers from the Perelman School of Medicine at the University of Pennsylvania took the unique approach of looking at the specific effects of ride-hailing within specific cities, rather than averaging data across multiple cities. And they found that there is a correlation between Uber and a decline in drunk driving, but not everywhere. Their findings were published this month in the American Journal of Epidemiology.

The team delved into whether ride-hailing affected crash rates in four cities: Las Vegas, Portland, Ore., Reno, Nev., and San Antonio, Texas — American cities in which Uber, the nation's largest ride-sharing company, launched, ceased, then resumed operations. And the results were mixed. Crashes involving alcohol decreased as Uber resumed services in Portland and San Antonio, but not Reno. And in no case did Uber's resumption of service result in fewer total injury crashes or serious crashes overall.

The authors suggest different effects may be due to characteristics of the cities themselves. "The observed variability may be due to the different conditions within these cities," said senior author Douglas Wiebe, an associate professor of epidemiology in Biostatistics, Epidemiology and Informatics, in a statement. "For example, in a denser urban center with congested traffic and limited parking a person may be more likely to use a ride-sharing service to get around."

“The observed variability may be due to the different conditions within these cities.”

Las Vegas attracts over 40 million tourists a year, many of whom will use Uber rather than a personal vehicle. The effect of ride-hailing on motor vehicle use and drunk driving in this city is likely to differ compared to locations that attract fewer tourists, the investigators found. Other variables, like a city’s topology and enforcement of drunk driving laws, can also effect whether residents use ride-hailing services.

The team further hypothesized that an increase in ride-hailing usage could correlate with an increase in auto accidents overall:

Because rideshare drivers must monitor a mobile device, and distraction in the form of glances away from the road increases crash risks, it is conceivable that rideshare drivers are at increased risks for crashing compared with non-rideshare drivers. Future research should examine whether such risks obtain for individual rideshare drivers, and whether any increase in distracted-driver crashes due to ridesharing is sufficient to wholly offset any reduction in alcohol-involved crashes.

Christopher Morrison, a postdoctoral fellow and the study’s lead author, said ride-hailing services may want to exercise caution when touting their impact on drunk driving. “It seems reasonable to report than ride-sharing is associated with fewer alcohol-involved crashes in some places,” Morrison said in an email. “For example, we found very strong effects in Portland, Oregon, where ride-sharing led to a 60 percent decrease in alcohol-involved crashes. But there are some very important caveats. We didn't observe these effects in all cities, and also the overall number of injury crashes didn't change in Portland or any other city, so it's also possible that ride-sharing increases non-alcohol crashes and there is no net change in the total number of crashes. We don't fully understand why that might be, so I think some caution is warranted.”

“I think some caution is warranted.”

The study wasn’t the first to examine the effect of ride-hailing on drunk driving. One found a 25 to 35 percent reduction in alcohol-related car accidents since Uber came to New York City in 2011, as compared to other places where the ride-hailing company doesn’t operate. Another looked at 100 densely populated counties across the US and found no correlation between the rollout of Uber and the number of traffic fatalities.

The Penn team also wasn’t the first to use the cessation and then resumption of Uber to examine the broader effects of ride-hailing services. Last month, a team of researchers examined the effect of Uber and Lyft on personal car ownership rates in Austin, Texas, where both services were temporarily shut down after stricter laws were passed. Unsurprisingly, the results were mixed.