Many European and Asian subway systems have sliding doors at the edge of the platform to keep people from jumping, or falling, onto the tracks. The United States hasn't deployed such barriers on its major metro lines - although a lot of airport trams use them - even though their benefits are becoming increasingly obvious.
Aside from saving lives - remember the kid who fell in front of a New York subway train? - they help keep stations cool and trains running on time.
How?
Anyone who's ridden a subway in the middle of summer knows stations become unbearably hot. Cities like Bangkok (MTR) have used platform doors to seal stations from tunnels, allowing them to crank the air conditioning without wasting energy keeping tunnels cool.
Keeping people from jumping, falling or being pushed onto the tracks, or simply keeping their stuff from falling down there, prevents delays. The Taipei Metro studied the effects of platfform gates onParis Métro Line 13 and found they cut delays by 69 percent. Platform screen doors, though, do not ensure that the subway system is 100% secure. One passenger got caught between the screen doors and the train in a Shanghai Metro station.
Retrofitting a station isn't cheap, though. Tapei, for example, spent about $9 million installing doors at two stations, and had to do the job at night. Even if American metro systems spent the money to install the barriers, maintaining them ors so that they actually open regularly is another story.
Photo by Flickr user Pixeloflight.
