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| Re: Lexington Avenue Line TPH (260249) | |
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Re: Lexington Avenue Line TPH |
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Posted by Stephen Bauman on Tue May 30 07:01:10 2006, in response to Re: Lexington Avenue Line TPH, posted by Red Line to Glenmont on Mon May 29 13:43:37 2006. This is just a theory, but from my experience with other European Subways, there often are just 5 50' cars on a line, so they pull into a station fast, decelerate really rapidly and then just take off, like Paris and Barcelona. In New York the trains are really long, and seem to slow down for stopping for a really long time in comparison. This could be the difference, that short light trains allow for closer spacing.Short trains do not mean higher braking and acceleration rates. Each car has its own motors and brakes. A 5 car train will have exactly the same horsepower/car as a 10 car train. Its power-to-weight ration is the same. It will have exactly the same acceleration. Ditto for braking. That said, the length of a train does affect maximum service levels. Let's examine this quantitatively. As stated above, the minimum allowable distance between trains does not change because the braking rates are the same. However, the distance between the fronts of the trains does because of longer trains. If the minimum allowable distance between trains be X feet, then the distance between the fronts would be 250+X for a 250 foot long train and 500+X for a 500 foot long train. That means that following train will have to travel 250 feet further to arrive at maximum service levels for longer trains. How long should that take? Suppose the trains are travelling at 30 mph. The extra time required to travel the extra 250 feet at that speed would be 6 seconds. So, given that 250 foot long trains could maintain 90 second headways (40 tph), then the minimum headway that could be expected for 500 foot long trains is 96 seconds or 37 tph. Of course, this is academic because Moscow train lengths are slightly longer than the 510 feet of the Lexington Ave expresses. Back to the drawing board? |
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