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| Re: TA is obsessed with CBTC, and ''New'' tech for no reason. (578525) | |||
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Re: TA is obsessed with CBTC, and ''New'' tech for no reason. |
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Posted by trainsarefun on Fri Feb 29 19:45:54 2008, in response to Re: TA is obsessed with CBTC, and ''New'' tech for no reason., posted by Stephen Bauman on Fri Feb 29 12:56:06 2008. Happened all the time, when the Flushing Line operated at 36 tph; the Queens Blvd Line operated at 34 tph and the Lex Express operated at 32 tph. They have signals and trippers within stations to allow the follower to approach the leader within the station at reduced speed.We can ask the people here who operate NYCT trains, but my uniform observation is that a following NYCT train does not enter the station until the the rear of the leading train has cleared the starting signal outbound. Effectively, the practice creates one enormous block running the length of the station. CBTC equipped rolling stock has the same emergency braking rate as the non-CBTC equipped rolling stock. The notion that CBTC will permit safe operation with 100 foot spacing between trains is a complete fiction. From the descriptions I've seen, I gather there's some kind of a speed control aspect to this. Otherwise the penalty brake application described would be insufficient to stop a train going above a certain speed. Current equipment is designed to have a maximum stopping distance of 275 feet (up from 250 feet for the pre-WWII fleet). If one adds a safety margin of 35%, this comes to 372 feet. This is the minimum safe distance between trains to guarantee that a follower will not rear-end its leader, should the leader decide to derail. The only way to shorten this distance is to improve emergency braking rates. This raises the question as to what is the spacing between trains. A train traveling at 30 mph will cover 4050 feet in 90 seconds. If that train is 600 feet long, the distance between leader and follower will be 3450 feet with 40 tph service levels. 30 tph service levels mean a 4800 foot distance between trains. I think that's correct, which is why I imagine that there's a speed control element to the CBTC system, which would enforce a penalty brake application - or even an emergency brake application, if required - when a train exceeded the speed permitted in that part of the block. But, of course, this is merely speculation on my part; although I don't see how it works otherwise. |
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