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| Re: what do you mean by Underruning 3rd rail? (was LIRR ESA) (256537) | |||
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Re: what do you mean by Underruning 3rd rail? (was LIRR ESA) |
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Posted by WillD on Mon May 22 16:34:56 2006, in response to what do you mean by Underruning 3rd rail?, posted by tramrunner on Mon May 22 16:07:43 2006. No, underrunning third rail is a specific type of third rail. In the US third rail comes in two varieties, over and under running. With an underrunning third rail the shoe sits under the rail and you can see this in NYC on the Metro North, in Philadelphia on the Market Frankford Line, and in all those cities I listed in the previous post. Overrunning third rail places the shoe over the rail (obviously enough) and while it's far more common in the North America and Asia it's somewhat less common in the rest of the world. The LIRR and NYC subway are the two most notable users of overrunning third rail. There's also a side-running third rail system, but it's not overly common in the US at all. You can see the different types of third rail on this illustration: Which was pulled from this page: http://www.railway-technical.com/etracp.html#Third-Rail The London Underground, Chicago 'L', some of Boston's subways, some of the Paris Metro, and the early small profile Berlin U-bahn lines (amongst others) use a simple top contact system without a cover (yes, London adds a fourth rail, but that's just another simple top contact third rail between the rails). NYC's Subway, the LIRR, BART, MARTA, PATCO, WMATA, Toronto's Subway, and many other North American systems, as well as at least the Athens, Tokyo, and Bucharest Metros, use a top contact third rail system with a cover. I honestly don't know of any side-contact third rail systems, so if anyone knows of an example I'd be happy to hear about it. Given the similarity in design of side and underrunning third rail systems it could be that I confused a few of them in my list in the last post. And of course the bottom contact, 'underrunning' third rail would include the systems I named in that last post. |
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