SEPTA subway trains and trolleys are equipped with automatic systems designed to prevent the kind of crash that killed nine people and injured scores in Washington.
But, as SEPTA operators and officials are acutely aware, so was the Washington system.
"Without knowing the cause of the accident there, it's hard to know if it could happen here," Jeffrey Knueppel, assistant general manager and chief engineer at SEPTA, said yesterday.
The Washington Metro accident Monday was probably a result of human error or equipment failure or signal malfunction, but it may be months before investigators pinpoint the cause.
"It's a horrible situation," Knueppel said. "Systems are designed to prevent something like this from happening. There is supposed to be a space that a train can't come into or shouldn't come into."
Knueppel said SEPTA had spent more than $200 million over the last decade "making sure our signal and control systems are as modern and safe as they can be."
Automatic anticollision systems are also in place on the PATCO High Speed Line that operates between Philadelphia and South Jersey.
The most vulnerable part of the regional commuter network is the SEPTA Regional Rail system; about 40 percent of it does not yet have automatic train control. There, safety depends on engineers responding to trackside and cab signals and instructions from dispatchers.
SEPTA is working to upgrade its entire rail network to a higher level of control - "positive train control" - by a federally mandated deadline of 2015. That system is designed to automatically stop trains that violate speed or spacing restrictions.
The federal deadline was established after a 2008 train collision in Los Angeles killed 25 people. An inattentive engineer on a Metrolink passenger train was using his cell phone when the train missed a signal and collided with a Union Pacific freight train.
In the Washington accident, one train smashed into the rear of a train stopped ahead of it. The Washington Metropolitan Area Transit Authority has a computer-operated control system that is supposed to prevent such crashes.
Similarly, SEPTA's Market-Frankford subway-elevated line, the Broad Street subway, and the Green Line's subway-surface trolleys all have automatic systems designed to stop trains that exceed speed restrictions or get too close to other trains.
Brakes are automatically applied when computers detect either speed or spacing violations.
In recent months, SEPTA has been struggling to fix chronic problems with the "communications-based train control" system designed to keep Green Line trolleys from colliding. Passengers and operators have complained that the system stops or slows trolleys too often, forcing frequent delays.
Michael Monastero, assistant chief engineer for communications and signals, said "significant progress" had been made in improving the Green Line system. Additional changes mean that "within a year, the system will be operating better than it is now."
After the Los Angeles crash, SEPTA toughened its restrictions against operators carrying cell phones. Now, operators of all SEPTA vehicles are forbidden to have a cell phone in their possession on a vehicle. They have SEPTA radios for communicating with dispatchers or police.
At PATCO, operators are required to turn off and store their cell phones or other electronic devices in their equipment bags, spokesman Ed Kasuba said. In an emergency, PATCO operators may use a cell phone when the train is stopped, he said.
In the earliest stages of its investigation into the Washington crash, the National Transportation Safety Board focused yesterday on why the passenger compartments within the subway cars fared so poorly.
The NTSB raised alarms in March 2006 about older-model subway cars after one of the cars in Washington's system collapsed like an accordion in an accident. The safety agency urged the Federal Transit Administration to develop crash standards that would address the telescoping of older cars and come up with a plan to remove aging trains that couldn't be structurally reinforced.
The nation's seven largest transit systems, including Washington's and SEPTA, depend on older cars for more than one-third of their fleets, according to a federal study published this spring.
The older cars are either near or past their usefulness, the report said.
Old subway cars experience the worst damage - a loss of what the NTSB calls "survivable space" - in crashes because most aren't adequately reinforced for impact.
The moving train in Monday's crash was more than 30 years old, officials said.
At SEPTA, the 218 cars on the Market-Frankford line were built in 1997, assistant general manager Luther Diggs said yesterday. The 123 cars on the Broad Street line were built in 1983-84, and the 140 trolleys were made in 1981.
The oldest Regional Rail cars date from 1963, and the newest from 1989, Diggs said. SEPTA is buying 120 new Silverliner rail cars to replace 73 of its oldest cars. The first of those are scheduled to be in service next May, and all are to be here by February or March 2011.
Diggs said that older subway and rail cars, like older automobiles, are less crashworthy than newer models. But, he said, even the most modern railcars will not fully protect passengers in a collision.
"The key," Diggs said, "is to have systems in place so they don't run into each other."