PHILADELPHIA (CBS) -- SEPTA will cease all operations early Sunday morning because of dangers posed to commuters and workers by Hurricane Irene.

This has never happened in the 45-plus-year history of SEPTA: a total shutdown of the far-reaching system, and it will come shortly after midnight Saturday.

“Buses, trolleys, subway, elevated, regional rail, all five counties — all service will stop at 12:30AM on Sunday morning,” said Mayor Nutter on Friday afternoon.

SEPTA spokesman Richard Maloney told KYW’s John McDevitt that the transit agency does not want to jeopardize the safety of its employees or the public.

“We do not want people stranded,” he said this afternoon.  “The mayor certainly remembers and the staff remembers the blizzards of just a few months ago, where we had people stranded in buses.  That was  for a couple of hours.  We could have people in buses swept away in buses in a storm that no one could get out to rescue them,” he said.

Certain Regional Rail lines –  the Airport line, Chestnut Hill West, Wilmington, Trenton, and  Paoli — were being shut down as early as 5PM Saturday afternoon because of similar shutdowns by Amtrak.  SEPTA said service across its entire system was not expected to resume until at least midday Sunday, following damage assessments and repairs. Service will resume on a route-by-route basis, based on conditions, SEPTA said.

Meantime, Nutter is opening three shelters at 6:00PM Saturday — at Bartram, Lincoln, and Roxborough High Schools — for residents who may have to evacuate and have nowhere else to go.

The mayor said any evacuations would be voluntary; he will not be issuing any such orders.

The Delaware River Port Authority says it will try to keep its bridges and PATCO service open as long as it is safe.

Flooding and high winds could close the Walt Whitman, Ben Franklin, Commodore Barry, or Betsy Ross bridges. Patco service could also be suspended.

The Ben Franklin Bridge pedestrian walkway will be closed Saturday and Sunday. The Riverlink Ferry will also not operate this weekend.

Reported by Mike Dunn, John McDevitt, Tim Jimenez, KYW Newsradio 1060