SEPTA Opens Up on MFL Cracks

60 Market-Frankford Line M-4 cars will remain sidelined while the cause of and repairs for cracked vent boxes and beams are dealt with. | Photo: Adam E. Moreira via Wikimedia Commons, used under CC-BY-SA-3.0

The bad news: About 60 Market-Frankford Line rapid transit cars will be out of commission for an indefinite period while SEPTA analyzes just what caused the cracks that spread from vent boxes to major load-bearing beams — or would have if a SEPTA maintenance shop worker hadn’t found cracks in two of those beams Friday night.

The good news: SEPTA has 218 cars in its M-4 fleet, which means that once undamaged cars can be uncoupled from damaged ones, it will have the 144 cars it needs to run regular peak-hour service. Detaching and reattaching the cars, however, will take a few days at least, and until then, there will be minor indigestion during the busiest travel times on the line. SEPTA will have enough buses to take care of the pain, though.

Those were the two most important takeaways from this afternoon’s news conference with SEPTA General Manger Jeff Knueppel.

Knueppel explained that the first sign of a problem came when a SEPTA maintenance employee found a crack in the body bolster of car 1091 during a scheduled overhaul Friday night. The body bolster is a major load-bearing beam that runs the width of the car and rests atop a truck, or wheel assembly. Each car has two of these beams; as the cars run in married pairs, each pair of cars has four.

Three of the four beams have ventilation boxes welded onto them. The vent boxes provide air to the traction motors. The cracks originated in the vent boxes and spread to the beams.

Knueppel explained that the welding process introduces weak points in the metal that could lead to cracks if they are overly stressed. “The crack starts from high stress at a bad detail, then when it starts opening, it attracts more stress to the location,” he said. “Then the crack can spread from something thin to something even thicker.”

That’s what happened on the two cars with cracked body equalizers. The welded-on vent boxes developed cracks that became more stressed, and the stress spread to the thicker equalizer beams.

(Similar weaknesses caused by welds have been determined to lead to the complete fracture of a support beam that forced the shutdown of the Delaware River Turnpike Bridge the week prior.)

“Given the seriousness of the crack and its location, any cars that we suspected of having cracks were removed from service over the weekend,” Knueppel said.

Knueppel explained that this was done to ensure rider safety. The next goal after that was to make sure there were enough vehicles to handle rush-hour traffic.

During a normal rush hour, Market-Frankford trains run at four- to five-minute headways. 144 cars are required to provide this level of service. Because only 60 cars will need to be sidelined while the stress fractures are analyzed and repaired, SEPTA will be able to run normal rush-hour service once married pairs are separated and undamaged cars joined together.

Monday morning’s commute ran with almost no disruption. “We had 60 buses in reserve” to handle the crush of passengers, “and we only used eight,” Knueppel said. Six buses ran eastbound from 52nd Street to 15th Street, and the other two ran westbound from Girard. “Our high spare ratio combined with a low defect occurrence rate has helped us keep a reasonable number of trains on the line.”

Knueppel said he expected more traffic than materialized this morning, a development he attributed to either “Super Bowl hangover” or passengers using alternate routes after news reports about the problem ran last night. He expects traffic to be heavier tomorrow morning but said that enough vehicles would be on hand to handle it.

“Safety is our highest priority, and we continually employ industry best practices to maintain safety,” Knueppel said. “We ask continued patience as we move quickly to address this problem.”

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