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- Newsgroups: rec.railroad
- Path: sparky!uunet!munnari.oz.au!mel.dit.csiro.au!squid.mel.dit.CSIRO.AU!ajw
- From: ajw@squid.mel.dit.CSIRO.AU (Andrew Waugh)
- Subject: Re: Auto Gates
- Message-ID: <1993Jan3.233645.3491@mel.dit.csiro.au>
- Sender: news@mel.dit.csiro.au
- Organization: CSIRO, Division of Information Technology, Melbourne
- References: <19010@mindlink.bc.ca>
- Date: Sun, 3 Jan 93 23:36:45 GMT
- Lines: 67
-
- In article <19010@mindlink.bc.ca> Steve_Hooper@mindlink.bc.ca (Steve Hooper) writes:
- >> khartman@fnala.fnal.gov writes:
- >> I have been interested in the methods used to "lift the gates" while
- >> a train is close to a crossing, but not moving. Setups that use the Diesel
- >> horn to activate the gates, or a slow moving train/timer.
- >
- >I find this an interesting concept. I have NEVER heard of such a thing....a
- >gate that operates off horn sounds. Not to call anyone a liar, but can you
- >verify 100% that the whistle is what activates the gates? I just find it
- >strange that a noise would work the gates. What would happen if a semi
- >pulled up to the crossing and blew his horn?
-
- While I certainly cannot verify that a particular level crossing in the U.S.
- has horn activated gates, I can confirm that this method of operation has
- been used in there.
-
- The Railway Gazette of 4 February 1955 included a short article on such
- an installation at Dumbarton on the Richmond, Fredericksburg & Potomac RR.
- This level crossing had 4 tracks, some of which were used as head shunts
- for a yard. While switching, the yard shunter would occupy the approach
- track circuits for the level crossing. The shunter would rarely occupy the
- crossing itself, and the gates would time out after 2 1/2 minutes of operation.
- If, after the gates had risen, the shunter decided to move across the crossing
- the gates could be reactivated by blowing the whistle. This was detected by
- an ordinary carbon (telephone) microphone and a relay would pick up if the
- sound was LOUD enough. This would restart the boom cycle.
-
- The use of track circuits was considered, but coded track circuits were already
- used with cab signalling and the addition of a number of short track circuits
- would have been expensive.
-
- >As I said, I could be 100% wrong here, but I can guarantee that in all the
- >areas of BC and Canada that I have worked, I have never encountered a
- >crossing acticvated by a whistle.
-
- As far as I am aware, no Australian (or British) railway has ever used anything
- similar either. In such a situation, i) the local railway would not allow
- the booms to work regularly for 2 1/2 minutes if the train was not going
- to enter the crossing -- this would be considered extremely dangerous; and
- ii) a pushbutton would be provided adjacent to the crossing to start the boom
- cycle when necessary for shunting.
-
- >Perhaps (again, I say perhaps, because maybe I am completely wrong here) you
- >are being fooled by a GCP. A GCP is a Grade Crossing Predictor. These are
- >fancy gates that instead of having the usual activation block in the rails,
- >actually detect MOVEMENT on the rails. Thus, if you are going 10 miles per
- >hour, the gates will go down when you are X amount of feet away from the
- >crossing. If you are doing 50, they will go down at Y feet from the
- >crossing. If you are stopped, they go up. As soon as you start moving
- >again, they go down.
-
- A GCP is basically a TDR (Time Domain Reflectometer) a device known and loved
- by those who maitain wiring plants such as ethernets. Periodically it sends
- a pulse down the rails and listens for disturbances in the reflections
- caused by a train approaching the crossing. (There are always some
- disturbances; a fixed short is applied to the track at a certain distance from
- the crossing so that the GCP can check its operation.) By timing the delay
- before the reflection returns, the GCP can work out how far the train is
- from the crossing. The next scan will give a new distance and by comparing
- the two, the GCP can estimate when to start the booms/flashing lights
- operating in order to give the optimum warning time (around 25 seconds).
- (At least that is how the local variety work; there may be other types.)
-
- It is a matter of considerable amusement to me that the first GCP in Victoria
- (and probably in Australia) was installed on a tourist railway!
-
- andrew waugh
-