While Muni replaces its clunky, chronically-broken ’90s-era trains with sleek, new Siemens-manufactured coaches, that good news may be curdled by an allegedly dangerous defect with new train doors.
According to the San Francisco Examiner, the doors on Siemens-built Muni coaches may trap and injure passengers who find themselves caught in the doors as they close.
The Examiner cites internal Muni documents indicating that four people have been stuck in the new doors since last September. Allegedly two passengers have been injured so far, including an instance of a woman getting dragged along a station platform and falling onto the tracks on April 12.
The San Francisco Municipal Transportation Agency contends that its trains have all passed the necessary safety tests.
You can read the full account of the alleged defect and resulting accidents here.
The April 12 accident comes on the same day Muni had to order new restrictions and inspections of Siemens cars after finding the coupler system (i.e., the mechanism that joins train cars together) defective.
The doors are supposed to be a big deal on Muni’s new trains: lighter, quieter, and supposedly more reliable than on the old cars. Previously, door and stair defects were the number one cause of Muni breakdowns.
Although train doors are supposed to automatically detect obstructions, Muni does warn riders to “please keep yourself and your possessions well clear of the doors upon entering and exiting the train.”
As City Lab noted in 2015, automatic doors with “sensitive edges” are designed to detect when they’ve hit a potential obstruction and then reopen.
This is, of course, meant to be a safety feature but can also encourage risky behaviors because riders assume that they’ll be safe if the door obstruction happens to be them.
Some of the new Muni trains have a new design that adds a second sensitive edge to the door systems, but only about 11 percent of the vehicles have this upgrade.
As the Federal Rail Administration’s guidelines on train door safety note, a sensitive edge usually works when an obstruction physically compresses it, which then signals to the train systems that something is wrong.
But modern trains have a variety of other tools to potentially detect problems, some of them remarkably sophisticated:
Other obstruction detection systems employ a tilting switch that detects when the door is bumped off balance by an obstruction and causes a reaction similar to doors employing a sensitive edge for obstruction detection.
There are also systems that use more sophisticated technologies to detect obstructions. These advanced systems monitor motor amperage, or air pressure in passenger cars with powered electro-pneumatic exterior side doors. These systems detect an increase in the electric current or air pressure, which tells the door safety system there is an obstruction in the exterior side doors.
Other advanced obstruction detection systems do not actually require the exterior side doors to impact an obstruction to detect it. Instead, they may use photo optics or laser light beams to prevent the door from closing if something interrupts a light beam that runs along the path of the closing exterior side door.
Of course, none of that does any good unless the train is functioning properly. So, again, seriously, as the voice on the intercom says, please stay clear of the doors.