The cable car incident that injured seven people Wednesday was caused by a bolt in the tracks that failed to trigger an alarm meant to alert operators of an obstruction, Muni officials said Thursday.
The cable car on the Powell-Hyde line was headed downtown Wednesday when it struck the bolt and abruptly stopped at Powell and Washington streets about 10:15 a.m. The sudden stop injured five passengers and two Muni workers. One of the injured passengers was a man in his 80s who suffered a head injury, fire Lt. Mindy Talmadge said.
After a review of the incident, Muni inspectors determined the bolt had come loose from a switch plate covering a portion of the tracks, said John Haley, director of transit for the San Francisco Municipal Transportation Agency, which operates Muni.
The 2-inch bolt was jammed at the top of the tracks, about 6 inches above the underground cables that are covered in sensors that trigger an alarm if there is an obstruction.
The alarm alerts operators to stop the vehicle, according to Haley. In Wednesday’s case, the bolt never touched the sensors. The alarm is usually triggered as many as two to three times a day, Haley said. However, the crews usually find trash, such as hot dog wrappers, that makes its way deep into the tracks.
The bolt incident has prompted a review of the track maintenance system, Haley said.
The more than 40 switches that are part of the cable car system are checked each night, and now a weekly check will test the tightness of the bolts securing the switch plates, he said.
Haley said there was nothing wrong with the cable car itself, but it did sustain some damage in the incident and is undergoing repairs to its underside. It is expected to be back in service within the next three days, he said.
The incident Wednesday delayed cable car service on the line, and buses were put in place while the scene of the accident was cleaned up and investigated. The accident also apparently delayed a cruise ship’s departure from The City.
Muni spokesman Paul Rose said Wednesday that the injured riders were passengers from a docked cruise ship. Port of San Francisco records show that the Costa Deliziosa, operated by Costa Crociere, was scheduled to leave port at 1 p.m. Wednesday.
Rose had said the agency had been in contact with the ship so that it would wait for the passengers while they were treated at a hospital. Documents show the ship did not leave port until about 10 p.m.