A computer error that cut signals to the brakes was found to be the culprit in a Monday morning Muni bus crash, and the San Francisco Examiner has learned that other braking problems may be widespread in the same type of bus, the most decrepit in Muni’s fleet.
Such revelations were highlighted in a document obtained by the Examiner and based on the experiences of Muni drivers who spoke under the condition of anonymity.
Monday’s glitch stopped the brakes from working on a 3-Jackson bus and sent it careening into a parked truck on Jackson and Scott streets. The driver of the bus was hospitalized due to pain in his neck and was later treated and released, according to San Francisco Municipal Transportation Agency spokesperson Paul Rose.
The front-crunched bus involved in the crash is from a cohort of 273 of Muni’s oldest vehicles, which were constructed by Electric Transit Inc. out of more than 800 in Muni’s fleet.
Those aging ETI buses run on most lines that use “trolley poles” to connect to wires, including the 30-Stockton in Chinatown, the 3-Jackson in Pacific Heights, the 31-Balboa in the Richmond District, the 22-Fillmore in the Fillmore, and the 33-Stanyan in the Haight.
The cause of the crash was revealed in a memo leaked to the Examiner. The SFMTA later provided the memo to the Examiner following inquiries based on its information.
“Click here to view the memo obtained by the San Francisco Examiner, which outlines the computer error that led to the Muni crash, Monday.”
“When the operator applied the foot brake, the computer should have signaled the traction motor to decelerate,” the memo reads. “It did not.”
“When the parking brake valve was activated, it too should have signaled the traction motor to reduce power,” the memo continues. “That communication link also failed.”
The reason for computer error is still unknown, according to the memo, and the SFMTA continues to investigate the issue. The memo does point to shorted out “thyristors,” which control electric power of buses through accelerator pedals and which were also the problem component in 100 BART trains earlier this year.
The memo was written by SFMTA Director of Transit John Haley and it reports preliminary findings into why the 3-Jackson bus rear-ended a parked truck Monday.
The crash occurred just outside Town School for Boys, an elementary and middle school in Pacific Heights. No bystanders were injured.
Though the ETI buses in Muni’s fleet are at least 13 years old, Haley said the particular computer error that caused the crash is rare.
“You’re talking about these vehicles operating above 100 million miles without this happening,” he said, “just to define [what we mean] when we say ‘rare.’”
However, Haley called the ETI-constructed buses a “nightmare” in a previous interview with the Examiner.
Multiple Muni operators, who asked their names not be used for fear of reprisal, told the Examiner they’ve experienced instances of brake failure with the ETI buses, in some cases causing them to fly through intersections without the ability to stop the vehicle.
One operator said that when the ETI buses experience a power surge, they go into what is called “restrictive mode,” which causes the bus to lose power and some braking ability.
“It’s imperative when that happens you do the best you can to stop immediately. You lose steering,” the operator said. “I’ve been driving down the street, and it goes into restrictive mode. That’s happened to me at least 10 times.”
The operator added, “Anytime it stops, it’s a danger for you and your passengers.”
This operator’s experience is reiterated in multiple operator stories told to the Examiner — and reflected in a separate memo the SFMTA sent, which was issued on the day of the collision and also provided to the Examiner by the SFMTA.
The second memo, also from Haley, said the SFMTA warned operators that if they see a “restrictive mode signal” on their bus while driving to pull over at the next stop and contact Muni central control by radio.
Restrictive mode is a diagnostic tool, Haley said, which can — in particular instances — stop steering and prevent brakes from working.
“It basically means there’s a situation that needs to be examined,” he said.
Haley said that in those cases, operators can stop a bus in other ways. They can apply the parking brake, switch the bus to neutral, press the “poles down” switch, hit the emergency power switch or turn the bus master run switch to “off.”
The SFMTA confirmed ETI buses across the fleet enter restrictive mode about once a day.
Haley acknowledged operators may need more frequent training in these procedures and that “orange paint” on some of the switches may help operators identify them more quickly in an emergency situation.
By December, Haley intends to order buses to replace the last of the 273 ETI buses. An expected order of 240 buses from New Flyer Inc. would replace them fully, he said.
“It’s our intention to retire every single one of them,” Haley said of the ETIs.
Still, that process may be years off, as the effort requires approvals from the SFMTA Board of Directors, Board of Supervisors, the Mayor’s Office and more.
Until then, the aging buses will continue to roam The City’s streets.