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| Re: R-160 Update (315443) | |||
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Re: R-160 Update |
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Posted by J trainloco on Mon Sep 25 17:34:56 2006, in response to Re: R-160 Update, posted by Stephen Bauman on Mon Sep 25 08:30:24 2006. You're confusing ATO with CBTC. It's possible to have ATO without CBTC. One example was the 42nd St Shuttle back in the 1960's.Yes, and its possible to have CBTC w/o ATO, as is the case on Canarsie. However, the eventuality of CBTC is to have ATO as well. CBTC cannot permit a follower to proceed until it can detect the leader's movements to a degree greater than its systemic accuracy. One factor is communications delay. The CBTC system permits a 2 second delay to/from each train. Thus, CBTC must factor in a worst case 4 second delay to the follower. 4 seconds at 40 mph translates into a 240 feet. This 240 foot distance, plus a safety margin for the brakes, is the minimum gap between leader and follower before the follower will start moving. N.B. I have not even considered errors in determining a train's position. That's all well and great, but when trains move out of stations, they're accelerating from 0mph. This means that if your 4 second figure is correct, the following train is beginning to proceed into the station with far less than 240'. But of even greater issue here is human control. Far to often, I've seen T/O's sit outside the station until the train ahead is fully outside of the station, and station time has automatically cleared. Additionally, Trains approaching stations that are occupied often slow down much too often, especially when they approach a station with a train that is already pulling out. CBTC will eliminate a lot of that unnecessary slowdown which will allow trailing trains to get into stations faster. More research is needed to determine why a follower catches up to its leader. There are two possibilities: the leader is going to slow or the follower is going too fast, relative to the schedule. Schedule padding makes the former possibility very unlikely. The cure for the latter possibility is not to try to make the follower even earlier by keying by. Ignore the padded schedule. If 5 trains are backed up behind one leader, then its obvious that the error here is on the leader being too slow. If every train has the same acceleration/top speed characteristics, then there's no reason for the leader to be so slow relative to the followers, even if the schedule dictates it. If the excuse is that supervision is holding the leader, then in reality the followers should all be getting held as well. What is needed is train supervision. CBTC is not required for train supervision. Moscow uses a simple clock at each station and operates at 43 tph. Paris uses a slightly more complicated clock at each station and operates at 36 tph. New York has virtually no train supervision and operates at 25 tph. NYCT is addressing the supervision issue. Lets see how well they do it with their new scheme. I ride trains on a track every morning that is able to process 28 tph. Generally, they do it without delays. Sometimes, the merge point where 18 of those trains merge with 10 of them experiences delays. Those occasions are not the norm. I would say that NYCT can operate up to 30tph on one track. |
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