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0028 Subway Doors
Date
1/10/91
Source
Risks 10.77 (Neumann, 2001)
Domain
Ground transportation
Function
Automatic doors
Guidelines
2.5.2-1
2.5.3-3
2.9-2
Description
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From Risks 10.77.
Vicious Subway Cars (was: Vicious Elevators)
Unix Guru-in-Training <elr%[email protected]>
Thu, 10 Jan 91 12:42:54 EST
Here’s a quick rundown on RISKS of stepping through the doors on a New York City subway car:
each of the twin doors can be as much as 3 inches open when the train starts moving, giving you a
maximum gap of 6 inches. Although an interlock prevents the train from starting while the doors are
open (called the “indication” by the train crew), the sensors aren’t too precise. People can (and do) get
dragged by moving cars when they’re stuck in the doors. Usually it’s their own fault—hyped up New
Yorkers who won’t wait the next three or five minutes for the next rush hour train (or ten or twenty
minutes off peak) blocking the doors open in the vain hope the conductor will re-open and let them in.
As a previous RISK poster noted, this all depends on the conductor’s mood and if s/he is in a hurry or
not. It also depends on their line supervisors: some managers emphasize speed, others passenger
safety.
A few years ago the Transit Authority had a problem with “doors opening enroute” on the older (pre1976 or so) cars—an individual door would open while the train was in motion, once on a speeding
express train (thankfully, no one was hurt). The TA rewired all their newer trains with an interlock so
that the emergency brake would activate if the doors opened while the train was in motion.
You can experiment with this safety interlock by attempting to force one of the doors open while the
train is moving. One day I observed two teenagers on the way to Brooklyn doing exactly that, thrilling
over pushing open a door two inches as the train sped through the tunnel. When I warned them that
they would kick in the emergency brake if they went too far they had a spell of enlightened self-interest
(it can take ten or fifteen minutes for the crew to reset the emergency brake) and left the poor door
alone.
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