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From bejm@ccfadm.eeg.ccf.org Mon Feb 5 10:24:21 EST 1996 (1.37.109.16/16.2) id AA102603858; Mon, 5 Feb 1996 10:24:18 -0500 Return-Path: Received: from ccfadm.eeg.ccf.org (ccfadm.eeg.ccf.org [139.137.100.1]) by (8.6.10/8.6.6.yuck) with ESMTP id JAA03438 for <>; Mon, 5 Feb 1996 09:20:25 -0600 Message-Id: <199602051520.JAA03438@> Received: by ccfadm.eeg.ccf.org (1.37.109.16/16.2) id AA099013462; Mon, 5 Feb 1996 10:17:42 -0500 From: Mark D Bej Subject: Re: Intertower commun., # of levers ... (fwd) To: ...@... (Signalling group) Date: Mon, 05 Feb 1996 10:17:40 EST X-Mailer: Elm [revision: 109.14] Status: RO > >> to slam all signals back into the frame. If B couldn't stop the train, he > >> sends Train Running Away on Right Line, and both of them pray. > > Typically, how many intervening signals, between B and C, would these > > trains have? > > NONE. There are no signals in the block, by definition. Again pointing out the differences in philosophy between American and European systems (if I may be permitted a gross generalization here) ... which is why the Pennsylvania, (?and others) terms their towers "Interlocking Station, Block Station, and Train Order Station". An Interlocking Station was one that controlled an interlocking, of course. A remotely-controlled interlocking had no Interlocking Station. Colloquially, these were called "tower"s, "cabin"s, etc. Note I don't mean here Jon's definition of "tower" and "cabin" as found in his newsletter, which is based on the structure's height, etc.. On the PRR, e.g., people referred to all of these things as "towers", even, e.g., Wilmington Tower, which was simply a room in the Wilmington (Delaware) station building. On other railroads I've seen terms such as "NY cabin" used for structures that clearly were "towers" in the physical (structural) sense. A Block Station was a location -- it did not need to be a physical building -- which could define the limits of a Manual Block. Some of these were simply a signpost along the tracks which were "remotely controlled" from the nearest tower. Some applied to only one of the tracks and not the other. A Train Order Station was, of course, a location where one could obtain a train order. Lately, there are locations with fax machines in locked wayside boxes. Previously, these were exclusively, or nearly exclusively, towers. A fourth item was a Block-Limit Station: a location, marked by a sign, marking the end of a block in unsignalled territory, "remotely controlled" by a tower operator or a dispatcher. Note that the word "Station" is used very generally in the above. A "Station" does not imply, necessarily, a physical building. A sign with the Station name along the right-of-way is sufficient. The older timetables, in the list of Stations for each main line and branch, had 4 columns, for: Interlocking; Interlocking Station; Block Station and Train Order Station; Block-Limit Station. The most common classifications were 3 X's in the first 3 columns (X indicated "open continuously"); X in the first column only (for remotely controlled interlockings); and a single X in the 4th column only (for Manual Block branches). The oddballs were, e.g., an X in column 1 and a P (P = part-time) in column 3, say at a location with a small cabin that is opened, by train order, as a Temporary Block Station. Some towers received a P in columns 2 and 3. A case in point was BRYN MAWR tower outside Philadelphia, terminus of the "Bryn Mawr turn", a local commuter trains that only runs to this "half-way point" of the Main Line, which did was not needed during the 3rd (night) shift and thus was a Part-Time Interlocking Station. The signals were fleeted (essentially, turned into automatic signals) overnight. > > What is "typical" signal spacing in general? In the States, > > e.g., it's 1-3 miles. > > In the block system, block spacing will be according to convenience (you > put a signal box at any station with pointwork) and traffic requirements > (you add passing boxes as needed). Perhaps every couple of miles on busy > lines, but several miles apart on less busy ones. I count IBS as being a > signal box, here. On a stretch of track as so: 2L 347 325 301 2L ITLK OO--| O=--| O--| O--| ITLK OO--| --|---------------|-----------|----------|----------|---------|-------------|-- |-o "A" |-o "B" 2R 2R signalled for westward running only, there would be electrical blocks marked by the "|" in the line of the track. There are 4 automatic blocks between B and A for westward trains. B's home signal 2L serves not only as the home signal for the interlocking, but also as the block signal between 2R and 301. On the other hand, an _eastward_ train that had to use this track would not have signals in his direction. The operator at A would have to (at the dispatcher's instruction) create a Manual Block between A and B. The train would receive a Restricting signal into the track between A and B, whether at the 2R signal of A or another signal, over intervening switches, and into the track shown in the map. He would then have no signals whatsoever, not even a "distant" signal, and would have orders to approach interlocking B prepared to stop (at B's 2R signal). The fact that the 2R is a dwarf signal reinforces the fact that the train is running "Against the Current of Traffic", under Manual Block rules. Such trains were, on the PRR at least, limited to 50 mph. So you see that here, a block to one train was not necessarily a block to another. Moreover, in the later years, (50s, I guess, and certainly the 60s, 70s) many all-Manual Block stations were removed. Their location was transformed into a Block-Limit Station, controlled either from the remaining (Manual) Block Station by radio, or controlled by the dispatcher directly. A train order may be transmitted to the engineer stating, e.g., "Pass SHIP Block-Limit Station as if a Clear-Block Signal were displayed". Most recently, even these few block stations were removed. At any rate, in the design of signalling on our mainlines here, the placement of towers (boxes), or interlockings, at blocks resembling braking distance, is _not_ a design consideration (at least to this observer). Braking distance, and train length (ever wait at a road crossing for a 140-car coal train? or a 120-car piggy-back train?), _is_ a general consideration in placing block signals (automatic signals). The interlockings are placed pursuant to the degree of control needed/desired. Block signalling between interlockings is then adjusted (usually the blocks are made _longer_) according to the needs for interlocking spacing. Interestingly, in their recent (1986/7) resignalling of the PRR's Middle Division, Conrail actually _added_ 3 interlockings, an uncommon move. And they _restored_ another (Michael: VIEW) at its original location where the tower had been demolished by a derailment some years before. On one particularly long stretch, the PRR went from LEWIS, MP [milepost] 165.7, to JACKS, MP 191.3, 25.6 miles (41 km) with no intervening interlockings; Conrail added 2 interlockings, making the inter-interlocking spacing 3.1 miles (end of a Controlled Siding exiting Lewistown Yard), 10.8, and 11.7 miles. The first (3.1 mi.) stretch probably has one (at most) intervening set of automatic signals. The latter 2 10-or-so-mile stretches probably have 3 or 4 sets of intervening automatic signals. -- Mark