Uber and Lyft have enjoyed explosive expansion in Philadelphia, with trips starting in the city increasing by 13 million in the last two years, according to data recently released by the Philadelphia Parking Authority.

That growth revealed a deep demand for convenient and plentiful cars for hire, industry representatives said, while others expressed concern about congestion caused by the service and the pressures that driving for a ride-share app puts on drivers.

"It's pretty clear that we're filling an important transportation need in Philadelphia," said Danielle Filson, a spokeswoman for Uber.

Along with an easy way to hail a ride, Philadelphia's two ride-share providers say they've increased mobility for people living in transit-poor communities and have played a role in reducing drunk driving, a claim some data support. They also, though, have been criticized for hurting public transit ridership, worsening street congestion, and creating a class of semi-professional drivers who work, sometimes full-time, with few benefits and uncertainty about how much money they will make for a day's labor.

"Any time you take a turn, any traffic jam you come across, there are always at least five or six Uber or Lyft drivers in it," said Roseann Robertson, a Chester woman who started driving for Uber five months ago. "That's probably why we don't get as much money as we used to."

These kinds of concerns drove New York City this month to put a temporary cap on ride-share vehicles there. The cap limits the number to those operating in the city now through the next year, according to the New York Times. The city also created a minimum wage for ride-share drivers.

Unlike New York City, neither Philadelphia city government or the PPA can order a cap. That power lies with the state legislature, and there is little enthusiasm to revisit the legislation that legalized ride sharing in Pennsylvania before next year, when it must be renewed. For the time being, city and state policy makers say they are watching and discussing New York City's policy shift.

"I'd like to see what happens in New York," said State Rep. Maria Donatucci, a Philadelphia Democrat and one of the negotiators on the original legislation. "I think it's something worth discussing."

Whether something similar could, or should, happen in Philadelphia depends on whom you ask.

An industry that didn't exist four years ago provided more than 10 million rides in April through June this year, the PPA data showed, more than three times as many trips than cabs provided during the same months in 2014, just before ride-share apps arrived in Philadelphia.

The numbers show that the ride-share industry is still growing, and capping it now could create a disparity between supply and demand.

"It's a completely unfeasible way to think about it," Campbell Matthews, a Lyft spokeswoman, said of the cap. "Demand is going to continue to increase. More people need rides to where they're going."

The 36 million Uber and Lyft trips originating in Philadelphia from July 2017 to June 2018 brought in about $376 million in revenue, 62 percent more than the companies reported earning in the previous year, according to tax revenue reported by the PPA. The key to success is convenience and speed, said David King, a professor at Arizona State University who studies transportation.

"These companies, Uber in particular," he said, "have this idea that service time, and the time between the request and the pickup, has to be as close to zero as possible."

Achieving that goal requires lots of drivers. Uber prides itself on being able to get a car to any location in the city within an average of five minutes, and in an interview Monday, Filson noted the greatest growth has been in parts of Philadelphia away from the city core, where there's less robust public transportation.

That's true outside the city as well. The company is providing 2½ times as many rides in Chester County as it did two years ago and more than three times as many rides in Bucks County, Filson said.

Exact numbers aren't available, but an estimated 25,000 ride-share vehicles operate in the city, the PPA reported.

Drivers of both taxis and ride-share vehicles said they would welcome a cap. Working for Uber and Lyft is becoming increasingly cannibalistic, they said. The glut of drivers means fewer trips per vehicle and less income. Robertson has a full-time job as a machinist, but her company hasn't been getting as many contracts recently, shrinking her pay. The lost salary already cost her a home to foreclosure, she said, so now on Fridays and Saturdays, between 9 p.m. and 4 a.m., she leaves her 1-year-old daughter with family to drive for Uber.

"I'm hoping Uber will be able to fix my financial problems," said Robertson, 33.

She typically drives in Philadelphia, she said, but in just five months, she's seen competition from other drivers cut into her earnings. When she started, she said, she typically could make $280 over both nights. Now she's just clearing $200.

Others have noted the overload of cars is particularly clear at Philadelphia International Airport, where ride-share drivers wait up to two hours in line in the hope of getting a traveler who needs a long ride home.

"The Uber drivers are sitting just as long as we are," said Ron Blount, president of the city's Taxi Workers Alliance, who also has begun speaking on behalf of ride-share drivers. "It's just horrible the way the situation is."

Transportation experts, and ride-share companies themselves, say New York City's situation is unique. Unlike most cities, New York's street traffic overwhelmingly consists of commercial vehicles, they said. While Uber and Lyft are likely contributing to traffic in Philadelphia, more personal vehicles are a bigger problem.

"I'm confident Uber and Lyft have contributed in some small way to the increase in congestion," said Erick Guerra, a University of Pennsylvania professor of urban design, "but not nearly as much as the economic growth and increase in population."

He said that the success of ride-share apps was evidence the city had a gap in transportation to fill and that a cap could unfairly limit access to a valuable service. Less extreme solutions could help Philadelphia, experts said, such as a congestion fee or minimum wage for drivers.

King also said New York's situation was unique and a cap shouldn't be replicated in Philadelphia. Concerns about drivers' wages, he said, would likely be resolved by market forces, as ride-share companies' efforts to keep prices low will eventually make driving for them unfeasible for most people.

"If Uber and Lyft want to retain their drivers, they'll have to pay attention to wages," he said. "I think the market will largely take care of it, but it's not like the market is magic, and the market won't happen overnight."