Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site brl-tgr.ARPA Path: utzoo!linus!philabs!cmcl2!seismo!brl-tgr!tgr!BSG@SCRC-STONY-BROOK.ARPA From: BSG@SCRC-STONY-BROOK.ARPA (Bernard S. Greenberg) Newsgroups: net.railroad Subject: Signaling on the NYC Subway Message-ID: <981@brl-tgr.ARPA> Date: Mon, 23-Dec-85 09:26:47 EST Article-I.D.: brl-tgr.981 Posted: Mon Dec 23 09:26:47 1985 Date-Received: Sat, 28-Dec-85 11:23:03 EST Sender: news@brl-tgr.ARPA Lines: 80 (I could not send To: nels@astrovax.uucp.arpa, somebody please forward if he's not on Railroad@rochester, which is certainly not likely) Date: 21 Dec 85 16:02:13 GMT From: Nels Anderson Could someone explain the signals used on New York's subway system? There is quite a variety of them, with different numbers of red, yellow and green lamps in various arrangements. -- Nels Anderson -- Nels Anderson Princeton University, Astrophysics {allegra,akgua,burl,cbosgd,decvax,ihnp4,noao,princeton,vax135}!astrovax!nels Date: 22 Dec 85 15:37:00 GMT From: "Allon G. Percus" Basically, when there is a standard signal with three lights, they mean the usual things: green -- proceed, amber -- proceed with caution expecting more amber and red signals to come, red -- come to a full stop -- if you don't, an automatic "tripper" from underneath the signal will force the emergency brakes on the train. A stack of one three-light signal on top of another means as follows: green over green -- proceed on main track, green over yellow -- proceed on diverging track, yellow over green -- proceed with caution on main track, yellow over yellow -- proceed with caution on diverging track, and red over anything OR anything over red -- come to a full stop. This is only part of the story. This is one of my favorite subjects in the world. The system Percus has just described is the newer system, which started on the BMT and IND, and is slowly being installed on the IRT. The upper head of a multi-head ("home") signal is indeed equivalent to a block signal, and the lower head is "green is straight, yellow is diverging", and reds only occur together. The following addenda to this are necessary: It is physically possible to pass a single red light by creeping up into the next section so slowly that it is noticed by the track circuit before you are tripped. This will lower the tripper. This action has been forbidden by regulation for about 10 years, but has not been modified out of the system. This is not possible for a double red light ("Stop and Stay"). Under a double red light, a single yellow can appear ("Call-on"), requiring an interaction to lower the tripper. The towerperson (all double signals involve an element of manual control) can elect this option only if the -only- reason the signal is red is the presence of trains in the blocks ahead of it (i.e., there are not switches set against it, signals set against it, etc.) There are several schemes of time-dependent indications (grade time, "station time"), I will not bore the list with the details unless someone prods me further... The older system of home signal indication, installed with the original IRT in 1904, is somewhat different, and corresponds to what is in use in much standard railroading. It also has the neat feature that it is extensible, which the newer system is not. A multi-headed signal in this scheme has one head corresponding to each possible route. Normally, the upper head is the "straight" route, and the lower the diverging. It is possible to have multiple diverging routes, and hence three heads. "Proceed with caution on diverging route" would be Red over Yellow (perhaps over another red if there are more than two). "Proceed on main route" would be Green over Red. Note that other than red over red, there are no shared aspects (the actual pattern of lights, as opposed to their "indication", or semantics) with the newer system. IRT home signals controlling paths over which there is no choice have single heads. You can tell them (as all old IRT home signals) by their red number-plates. You cannot force the tripper down by approach (automatic key-by), so their "stop" indication indeed has the force of home signals. I can go on at any length or depth on this that anyone wants to hear. I spent a large part of my childhood and adolescence in NY roaming the subways, communicating with the then-NYCTA, collecting prints, circuit diagrams, interlocking plans, etc....