Night owls in Philadelphia will find the Broad Street and Market Frankford subway lines open 24 hours on weekends, beginning Saturday night.

SEPTA is piloting the overnight service this summer in response to increased demand for late-night service, said Jeff Knueppel, deputy general manager.

"Philadelphia has changed. More people are moving back to live in the city, and more people are coming into the city to enjoy the restaurants and experience the nightlife," he said.

"City officials, community and business leaders, and our riders asked SEPTA to run trains after midnight. We heard them."

Trains will run every 20 minutes from midnight to 5 a.m. on Friday and Saturday nights throughout the summer. They will replace late-night buses, which will not be running weekends. The cost of operating the trains for the summer pilot will be around $450,000.

Depending on its success in attracting ridership, SEPTA will consider making the service permanent.