The aging infrastructure carries millions of riders across the region, but it is wearing down.
Executives say there is too little funding to keep pace with need.
At a SEPTA board meeting on Thursday, officials offered a projection of what could happen within a few years without a major infusion of new money from the state.
"This is devastating. Nine of the 13 rail lines go down and even the four that continue to operate cannot run the level of service we do today," said Jeff Knueppel of SEPTA.
City trolley routes will become a thing of the past, SEPTA says, converted to bus routes.
SEPTA said it needs $6.5 billion over the next 10 years to keep pace with other big metro area mass transit lines.
"And by 2023 it's just not prudent to run a 42-year-old Kawasaki cars in the Broad Street subway at 70 miles per hour down express tracks, so we have local service only," said Knueppel.
"We're at a point where the state has a vested interest in helping us as far as economic development. We are the economic engine of this region," said Pasquale Deon, SEPTA board chairman.
As it stands, SEPTA said it will start to implement this budget in 2014, which will eventually cut off rail service to some 89,000 daily passengers.