Friday, December 16, 2011

Are Metro's Slow Escalators Actually More Dangerous?

This is a nice find from Mike:
Who brags about their escalators being 25 percent slower than normal escalators? Metro! That's who!
In case you can't make out the sign, it says:
Most escalators--like the ones you ride at shopping malls--travel at about 120 feet per minute (fpm). A Metro escalator travels at 90 feet per minute. We just think it's good to slow down, enjoy the view and be safe.
Whatever. Who comes up with this stuff, and how much do they get paid? I'll do it for half.

Assuming you find a working escalator, the slow speed definitely encourages a lot of people to walk. Apparently wear and tear increases if you walk a moving escalator.

Furthermore, I found this old report that actually included Metro, which "provides evaluations of special design features associated with escalators used in rail transit systems." I guess some of the findings could be outdated, but I doubt this one is.

Turns out slower escalators are dangerous.
The preferred design is a dual speed escalator. The 120 fpm speed should be used during the peak hours and 90 fpm during the off-peak hours. Even though the hourly capacity is not linearly related to speed, the increase in escalator capacity at the higher speed reduces problems of overcrowding at high volume stations. At low volume stations existing data indicates no real advantages to the higher speed. Escalators over 40 ft high (three level changes) should utilize the speed of 120 fpm to reduce extended travel time on escalators. Excessive travel times result in movement of passengers resulting in a hazardous operating environment.
Nice job Metro.

Update from a Metro escalator expert:
The code for escalators allowed a max speed of 125 fpm with A17.1d -2000 and earlier. A17.1-2000 and later sets the max speed at 100 fpm. The min. speed can not be less than 10 fpm. The early units in Metro had two speeds 90 fpm and 120 fpm because they were driven by two speed ac motors. The newer units have a variable frequency drive and so can be set to any speed. I believe that Metro uses 90 fpm because the early units could be made to run at 90 fpm by disabling the high speed contacts and running only on the slow speed. I think this was done because they felt it was safer and easier for people to get on and off ( especially older folks and people who are a little afraid of escalators). The slower speed also reduces wear and tear on the units.
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