Muni is set to run one-car trains instead of two-car trains following the discovery of an engineering defect on their new trains.

Vital link between two Muni train cars ‘failed’ while carrying passengers

A Muni train carrying passengers suffered a mechanical failure causing two rail cars to reportedly loosen and bump into each other

A Muni train carrying passengers suffered a mechanical failure causing two rail cars to reportedly loosen and bump into each other Wednesday, the San Francisco Examiner has learned.

While the mechanical failure did not injure any passengers, its revelation comes at a crucial time for the agency as train manufacturer Siemens informed Muni, also on Wednesday, that the engineering defect affects all 68 of its brand-new trains, the first batch to be delivered in Muni’s future $1.1 billion fleet.

The K-Ingleside Muni train was out in service near West Portal station, carrying passengers, when a shear pin holding two rail cars together “failed,” according to an internal Muni memo obtained by the Examiner from a source who requested anonymity for fear of reprisal, and later confirmed by the SFMTA.

“The operator reported to her Supervisor that it felt like her train was being continually rear ended [sic],” Julie Kirschbaum, San Francisco Municipal Transportation Agency director of transit, wrote to Muni staff in that memo, Wednesday.

Importantly, there’s no such thing as a “runaway train” in Muni’s light rail vehicle fleet, a point Emmanuel “Manny” Enriquez, the supervising engineer who leads the new train procurement, emphasized to reporters on a rail yard tour, Tuesday.

When a train comes loose with no control of its brakes, the trains are designed to automatically stop.

And on Wednesday the train cars did not separate, Kirschbaum wrote in the email, though that does not explain how the trains were rear-ending one another. After the operator reported the mechanical failure passengers disembarked the train and it was taken out of service and taken to SFMTA’s Green Yard.

“There does not appear to be a single event (collision, etc.) that caused of the failure [sic], but our investigation is ongoing,” Kirschbaum wrote.

That very same day, the new fleet’s manufacturer, Siemens, informed SFMTA that the shear pin failures were fleetwide — just six months after the agency announced that the problem, which was already known, was fixed.

What does that mean for Muni riders now? Rail commuters, get ready to be squeezed.

Muni is set to run one-car trains instead of two-car trains, after the engineering defect was revealed. And shorter trains means the ones that are running will be packed tight.

As many as 14 train cars out of 40 running at any one time will be affected, according to SFMTA. As many as 140,000 passengers take trips aboard Muni’s metro system every day.

“We are confident we can manage the capacity” SFMTA spokesperson Erica Kato said, but “riders might be a bit more squeezed.”

The engineering defect Siemens identified is called “shear pin fatigue.” That shear pin is a vital component helping to join trains together working with a “coupler.” Muni sources told the Examiner the problem is with the coupler design itself. In her letter to staff, Kirschbaum said the shear pins would be redesigned, but she did not mention redesigning the couplers themselves.

Importantly, shear pins are designed to fail — but not as fast as they have been.

The shear pins being used in the cars are lasting only about three months, far less than they’re expected to by the manufacturer. Siemens will pay for the shear-pin replacement, Kato said.

“They will make this a top priority,” she added.

Problems aboard the new trains have abounded: From doors that clamped down on a woman’s hand and dragged her to the tracks, seats that were too tall and slippery for passengers that drew widespread complaints, and too-hard brakes that wore down the train’s wheels far-before their expected end of life.

Most of those problems have either been fixed or have planned fixes on the way. But the return of the shear pin issue caught Muni by surprise this week.

The defect also emerged just weeks after SFMTA launched its final new Muni train from its first purchase for testing, its 68th new train car.

SFMTA had hoped to show the Board of Supervisors its trains were running properly so the board would authorize more than $60 million to help accelerate production of its second batch of rail cars, 151 of them.

Now the first batch is suffering mechanical issues once again.

joe@sfexaminer.com

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