Creating a new mass transit system isn't easy.

But Alison Cohen has helped launch five of them - from her home office in Mount Airy.

Cohen, 40, is chief executive of Bicycle Transit Systems, the start-up that beat out five other companies for the contract to run Philadelphia's newly announced bike-share system, Indego, slated to launch in the spring.

She has also launched systems in Boston, New York, Washington, and Melbourne, Australia.

Because her company is in charge of maintaining bikes, handling customer service, and stocking stations, whether bike-share succeeds or fails in Philadelphia rests in large part on her shoulders.

"It's critical to the success of the system," Andrew Stober, chief of staff at the Mayor's Office of Transportation and Utilities, said late last week. He thinks Cohen is ready for the job.

"I don't think there's anyone in North America who's thought more deeply about bike sharing than Alison Cohen," he said.

Cohen didn't plan to go into this field - in fact, it didn't exist when she graduated from Lower Merion High School in 1992 (a standout athlete, she held the school's basketball scoring record until Kobe Bryant shattered it).

She studied physics at the University of Virginia, played professional tennis for three years, and held jobs in finance and environmental consulting.

But, while living in Boston in 2007, she read about the new Paris bike-share system. She spotted an opportunity to create something similar here.

Cohen imagined U.S. bike-sharing would emerge from the private sector, as car-sharing has. She built a company around the idea, pitching single-point, corporate bike-share programs that could one day be connected.

Then the chance to submit a proposal for a citywide Boston bike-share system came up.

"I was wrong in terms of how bike-share would start, but I was at the right place at the right time," she said in an interview Sunday. "I was the flag-bearer for bike-share in Boston."

Her team, Alta Bicycle Share, won the contract to run Boston's Hubway system and later launched New York's Citi Bike and D.C.'s Capital Bikeshare.

Today, there are about 40 systems in the country, and Cohen sees lots of potential. She's done studies for smaller cities, including Eugene, Ore., and Frederick, Md., that consider it a key to revitalizing their urban cores and attracting young residents.

She said that's what she loves about this business: "As a really small company, you can have a huge impact on people's lives and on these cities."

It hasn't always been a smooth ride, though.

The biggest bump in the road came with the troubled launch of Citi Bike. There were problems with software and with the equipment manufacturer - and Cohen left Alta, she said, after disagreements over how to handle that situation.

In 2013, she teamed with former Alta colleagues to launch Bicycle Transit Systems. Their Philly launch will take lessons from New York and other cities, she said. One was selecting B-cycle to supply the equipment.

The system will employ about 20 people on an annual operating budget of $1.8 million. And Bicycle Transit Systems will finally get a headquarters outside Cohen's house.

Cohen - who has three children, including newborn twins, with her wife, Nurit Bloom - also has other projects underway. Her company recently took over Oklahoma City's bike-share program and is bidding to run one in Los Angeles.

But the Indego launch is a homecoming.

"It will be nice to be able to use it and to be able to see how it changes people's lives."