MIAMI (AP) — In South Florida, clubs are open late, booze flows freely and the public transportation system leaves a lot to be desired. But the number of drunk drivers on the road appears to be going down.

At least the number of them getting caught is.

In the past four years, DUI arrests made by Miami-Dade's two largest police departments have plummeted. In Miami-Dade, the largest police department in the Southeastern U.S., arrests were down a staggering 65 percent in 2017 from four years earlier. Miami-Dade police arrested more than 1,500 people each year from 2013 through 2015. Only 594 were arrested on the same charge last year.

Miami's numbers weren't quite as eye-popping, though they also declined a lot. Miami police arrested 461 people on DUI charges in 2013. By 2015, the number dropped to 321 and has leveled off since — a 31 percent decrease.

Some of the credit probably goes to the rise of ride-sharing companies like Uber and Lyft. Their increasing popularity coincided almost directly with the drop in DUI arrests but studies also have found impacts varied from city to city.

Other factors also play in, say those who track the numbers. Some attribute the drop-off to a more educated public. Others point to more pro-active law enforcement and a trendy distaste for driving by the millennial generation.

"The reality is, it's really hard to know the complete impact," said David Pinsker, Florida's executive director for Mothers Against Drunk Driving, an agency that works closely with dozens of police departments across the nation to curb the potentially deadly mixture of booze and motorized vehicles. "I think it's just really hard to pinpoint exactly what ride-sharing has done. We know it's had an impact. I can say that certainly. But I can't put a number on it."

Nationally, a 2017 study found mixed results in determining whether ride-sharing is responsible for a lower DUI rate or accidents. Researchers at the Perelman School of Medicine at the University of Pennsylvania took a look at four cities that had ride-sharing services, stopped, then started the service up again.

The results varied in data from the years 2013 to 2016. When ride-sharing was available, DUI's dropped in Portland, Oregon, by almost 60 percent, the study found. Similar numbers were found in San Antonio, Texas. But the numbers didn't change much in Reno, Nevada, a tourist mecca. The researchers also found little change in Las Vegas, because, like in Reno, the population is swollen with out-of-towners who take taxis, public transportation or walk.

Miami Mayor Francis Suarez raised the decline a few weeks ago with the Miami Herald Editorial Board while discussing parking concerns related to a plan to build a soccer stadium at International Links Melreese Country Club . His 50 percent decline estimate was off slightly but close. The mayor attributed the drop to ride-sharing, a transportation option he argued would also reduce parking demands for the project.

There have been only a limited number of studies analyzing whether ride-sharing contributes to a decline in drunk driving. In 2015, MADD teamed up with Uber and found that drunk-driving crashes for people under 30 years of age decreased by 6.5 percent in markets where ride-sharing was launched. Two years later, a team of researchers at the University of Pennsylvania found a correlation between ride-sharing and a decline in drunk driving but not in every city.

Javier Correoso, the public affairs manager for Uber in Florida, said his company has worked closely with MADD on getting word out about how easy it is to catch a ride during the two booziest holidays of the year, Halloween and New Year's Eve.

"I think our presence and our growth in South Florida go hand-in-hand with giving our riders an alternative to getting behind the wheel when they're drinking," he said.

But Correoso wouldn't go so far as to say ride-sharing has definitively cut down on drunk driving and that the numbers have dropped because millennials are driving less and using Uber more.

Maia Walker, a 21-year-old who graduated from Miami Country Day High School and has spent the summer working in New York City, never got her driver's license. She said she found little use for it with ride-sharing so easily available.

"I try not to use it so much during the day. But going out at night, none of us ever drive. We always take ride-shares," she said. "Even when we were in high school going to parties we used Uber. Split with four people, it was like $5 each. It's so much better than any other option."

Miami-Dade police have had a sergeant and five officers working on a DUI squad for years. Often, others join in and up to 15 units saturate the roadways looking for drunk drivers. Detective and spokesman Alvaro Zabaleta said DUI arrests have dropped because of all of the above — beefed up enforcement, working with MADD to educate and millennials preferring letting others do the driving.

"I think all of it together is where I feel the success has come from," he said.

Miami police Lt. Joaquin Freire lost his sister Gloria Hall to a drunk driver in Hialeah more than a decade ago. He's since moved on to command the traffic enforcement unit in the city. He said patrols have been beefed up to enforce driving and drinking laws.

Freire patched together the city's first DUI detail in January. Motormen, more commonly known as motorcylce cops, have been instructed to be more aggressive in enforcing drunk driving laws after dark.

"Ride-sharing has definitely impacted things. Everybody now with their Smartphones, there's always an Uber around. Uber and Lyft have definitely been an impact," he said. "But we're still out there."

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Information from: The Miami Herald, http://www.herald.com