WaI vs. WaP: NYC Subway Edition
As an infrastructure nerd, I found it fascinating.
But as a student of human factors, this bit also stood out to me:
Four years later, signal failure caused one train to rear-end another on the Williamsburg Bridge, the fourth such collision in two years. The driver died, and several dozen passengers were injured. The train was going at 36 mph through a signal designed for trains whose maximum speed was 28 mph; even with improved braking, the stopping distance was too long. The MTA said the driver could have seen the train ahead, but the driver had been too fatigued. The NYCT responded by slapping a 25 mph speed restriction on all bridges, building on the findings after the Union Square derailment.
After the accident, the NYCT also reduced the acceleration rates of the subway trains to match the rates of the older trains. Subways and regional trains around the world accelerate at 2.5 mph per second or even faster, but in New York acceleration is restricted to about 1 mph per second.
Unfortunately, these modifications to the operating procedure made the old signals less reliable. An MTA source explains that the NYCT did not always recalibrate the signals correctly for the reduced speed. Consequently, train drivers don’t trust the signals and go even slower for safety. Train drivers have internalized this practice, and even when the signals are reliable they often go slower than they could, to give themselves a safety margin to avoid crossing a stop signal.
If you live in NYC (or you just wonder why the subway system may seem “off” if you’re visiting), the article is worth a read.
But this is yet another example of “Work as Imagined” versus “Work as Performed” in a complex system, the rational tradeoffs (when you know the reasons behind them) workers make in the pursuit of production, and just how much that dichotomy between what we imagine happens in the trenches versus what actually happens in the trenches can impact to our lives.
(Or, in this case, our daily commute.)