PHILADELPHIA (AP) _ An executive who helped launch the city's newest newspaper, distributed free at city transit stations, has resigned, six months after its first edition.

Managing director Jack Roberts, who helped launch Metro in January, said Thursday he will step down next week to teach at a university. He didn't identify where. Roberts, 51, also cited family reasons for leaving.

The tabloid, owned by Sweden-based Metro International, is published five days a week and is distributed free at bus, train and subway stops and on buses.

The Southeastern Pennsylvania Transportation Authority permits distribution in those places in return for $30,000 a month in ad revenue and one page in each paper to communicate with its riders.

A federal lawsuit filed by the owners of The Philadelphia Inquirer and Philadelphia Daily News, USA Today and The New York Times argues that the contract is an unconstitutional infringement on press freedoms because other publications cannot be sold in the same areas.

A federal appeals court in February refused to issue an injunction to block distribution of Metro. It has not yet heard arguments on the merits of the case.