Starting Friday, Uber is debuting a new service in Philadelphia, uberPOOL. It's the same drivers who make up the UberX fleet offering it, meaning it is still not technically legal, since these motorists' vehicles aren't regulated by the Philadelphia Parking Authority. 

UberPOOL is exactly what it sounds like: car pooling through Uber. Two people who don't know each other but are heading in the same direction can share the same Uber ride, and it's cheaper for both, since each passenger only pays for their portion of the ride, making the trip about 30 percent cheaper per passenger, Uber said, regardless of whether a second passenger gets picked up.

The new service is appearing in the midst of escalating friction between the PPA and ride hailing services. Recently released emails showed the PPA discussing with city cab owners opposition to UberX in Philly. The emails, from fall 2014, showed PPA officials urging taxi medallion owners to lobby lawmakers to "carve out" Philadelphia from any bill that would legalize UberX and Lyft, a competing service, in Pennsylvania. Both services operate legally in the rest of the state.

Uber has accused the PPA of being "untrustworthy," and unaccountable. The PPA says Uber is the one without accountability, and said their efforts haven't been to kill UberX but to give it oversight that would guarantee safe vehicles and drivers. 

UberPOOL began in San Francisco in 2014 and is offered in 20 American cities and begins operation at noon Friday in Center City, South Philly, Navy Yard, the sports complex, University City, Fairmont, Temple University, Kensington, Northern Liberties, Fishtown, East Falls and Manayunk. Once it debuts, the Uber app will include a "request uberPOOL" option. The service accepts up to two passengers per destination.

A FAQ sheet issued by Uber is available here. Among the wrinkles in the usual UberX service, drivers will only wait two minutes since there's another passenger waiting, and missing that deadline results in a $2 fee. A rider also can't change destinations after requesting a ride.