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| Re: R-160 Update (315287) | |||
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Re: R-160 Update |
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Posted by Stephen Bauman on Mon Sep 25 08:30:24 2006, in response to Re: R-160 Update, posted by J trainloco on Sun Sep 24 22:21:53 2006. If CBTC works1. It doesn't take into account the operator's ability. 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. 2. As soon as the train in the station begins to move, the one behind can do the same. 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. Consider the present block system. The uncertainty for the leader's location is the block length. Block lengths at a station's entrance and in the station are fairly short - on the order of 200 feet or less. As the leader in the station starts moving, it clears the blocks leading into the station. The follower can start moving, as soon as the leader has moved 400 feet. Check the action of the station approach signals as trains leave stations to verify this. I have. Net difference between CBTC and the current block system is negligible. sometimes, trains catch up to their leader...If keying by were not only allowed, but encouraged, I rode the Flushing train and Queens Blvd express, when they ran 36 and 34 tph, respectively. They did not key by. How do I know? They did not encounter red signals - not even yellow signals. They encountered green signals (for a split second). 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. 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. |
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