In an unprecedented step, the dominant mass transit serving the Philadelphia area will suspend all service – buses, trains and subways – in preparation for Hurricane Irene.

The Southeastern Pennsylvania Transportation Authority – better known as SEPTA – will cancel all its lines between 12:30 a.m. Sunday morning until noon Sunday.

On its website SEPTA -- which serves Bucks, Chester, Delaware, Montgomery, and Philadelphia Counties – cited the storm’s potential for sustained high winds, heavy rains, and the potential for severe flooding, downed trees, and wires.”

SEPTA -- which carries about 200,000 people on a typical Sunday – said it will “monitor the situation through the overnight and determine our ability to run service after [Sunday] 12 Noon.”

In addition, because of Amtrak’s decision to shut down the Northeast Corridor service, half of SEPTA's regional rail lines - the Chestnut Hill West, Wilmington (Del.), Trenton (N.J.), Paoli and Airport lines - will suspend service on 5 p.m. Saturday because they use Amtrak lines.

SEPTA spokesman Richard Maloney said this will mark the first time in the agency’s history that it will completely shutdown.

It would be absolutely unprofessional for us to try and provide the service and endanger our employees or, particularly, the public, Maloney said Friday. We do not want people stranded.

Meanwhile, the mayor of Philadelphia, Michael Nutter, said the city will not impose a mandatory evacuation order for low-lying, flood-prone areas of the city, but will open three high schools -- Roxborough, Bartram and Lincoln High Schools -- as shelters.

Nutter urged people in vulnerable areas to exercise good judgment. He also asked residents to remain indoors for the duration of the storm, which is expected to last for twelve hours and dump up to 9 inches of rain and blast winds of up to 60 miles per hour.

Pennsylvania governor Tom Corbett, who has already declared a state of emergency, said in a statement: We are urging all Pennsylvanians to take action now to be prepared. We will continue to monitor this changing situation statewide and plan for all possible emergencies. Should the need arise, we will be able to help as quickly and efficiently as possible.