METRA's 16TH ST Tower to Close, Following CY

I just got word that METRA's famed 16TH ST Interlocking tower at the triple crossing of the Alton (CNIC), Saint Charles Air Line and the Rock Island, is slated in close in early April. Built in 1901, the tower and its original Taylor Model 2 pistol grip type interlocking machine have been in continuous service since 1901 or 124 years! Unlike some other towers where the closure comes out of left field, this one has been telegraphed for some time. 16TH ST (and presumably its interlocking hardware) has been falling into increasing disrepair and I am honestly shocked it did not manage to catch fire or fall down on its own.

16TH ST in 2017, it looks worse now.

Cost cutting on the part of Canadian National, starting in 2019, have reduced the 12 diamond plant to just 4, as what had been a Y split of two double track main lines crossing another double track main line, was reduced to two single track lines crossing a double track line. It was clear for some time that once all the work was finished to rebuild the complex crossing to some sort of new standard, the tower would be closed.

Given the wooden tower's condition, its also pretty clear that the tower is beyond saving, even in situ, but I'd expect parts of the interlocking machine and model board to make their way into preservation similar to what we saw with CALUMET about a decade ago. Anyone looking to grab some photos during the final days in service can snag a view from the corner of 16th St and Clark.

In other bad news, the late model Chicago Northwestern CY tower has also been closed by Union Pacific as a downstream outcome of UP looking to transfer METRA commuter operations to METRA itself. The operator at CY had control of the local interlocking and much of the METRA UP-Northwest line, where Metra was the primary source of traffic. This was likely a way to better allocate the costs of dispatching the line. Run from a video display interface for years, control might end up in the METRA operation's center with staffing of the still open LAKE ST tower, also taken over by METRA.

Unlike 16TH ST, CY is of far more sturdy construction and will likely serve as an maintenance base for decades to come like its sibling KEDZIE tower on the UP-WEST line. With these two closures the Chicago area will be reduced to four traditional interlocking towers on main line railroads, LAKE ST (CNW), TOWER A-2 (Western Ave), TOWER B-17 and JB.  Three of these towers are on the METRA UP/CNW-West Line between the CNW Terminal and West Chicago with the fourth being on the Milwaukee West Line.

GRESHAM JCT's Sequence Switches Explained

 Years ago I wrote up a profile of METRA's GRESHAM JUNCTION tower on the Rock Island division south of Chicago.  Not only had GRESHAM JUNCTION managed to stay open into the 21st Century, it was a unique North American example of a sequence switch interlocking. Supplied by the Standard Telephone and Cables Company of London, the interlocking used telecom grade sequence switches to carry out the interlocking functions instead of relays.

In my original post I provide photos of the equipment as well as a general concept of how sequence switches work and some sequence switch interlocking circuit diagrams from the UK, but without time and access to the equipment or someone who was intimately knowledgeable about how it functions, my commentary had to remain at a very high level.  Fortunately, the gang from the Connections Museum in Seattle is on the case because sequence switches is pretty much how Bell Number 1 Panel central office machines functioned (again, as opposed to later relay based technologies). I could try to go into things, but fortunately the museum's YouTube channel has video that is specifically about how sequence switches work. 

Once you see them in action at the Connections Museum, their function in the photos from GRESHAM JCT will become obvious. Of particular note is the function of the magnetic clutch mechanism that rotates the switch spindle. Perhaps if I stare at things enough I can determine what each sequence switch corresponds to in the interlocking.  Is each a complete route? An entrance? An exit? An entrance-exit combination? Let me know in the comments if you figure it out.  BTW, if you like this video take some time to watch the rest of the Museum's content.  It's top notch and does a superb job of explaining some normally opaque topics in the realm of pre-modern telephone switching technology.

According to the Timetable - METRA Beverly Branch

While Timetable and Train Order operation isn't quite dead yet, the "timetable" part of it almost certainly is, even on the one line that officially still uses the system. This is because for all the talk of superior and inferior trains the LIRR does a pretty good job at making sure trains know explicitly when they have to take sidings due to the Manual Block system that covers the more traditional T&TO. Of course that is what I thought until I started going some research on METRA's Blue Island interlocking tower located on their Rock Island division.

Anyone familiarizing themselves with the METRA commuter network may have noticed the strange lack of any automatic signaling system on the Beverly Branch portion of the Rock Island District. The Beverly Branch is an interurban themed loop off the Rock Island main line that sees the majority of Rock Island district trains save for a few rush hour express runs. Running 6.5 miles from Gresham Junction to Blue Island – Vermont Street about 5 miles of that is not covered by any sort of automatic signaling, which under GCOR means ABS or CTC rules. Of course what the line lacks in signals it makes up for in stations with a total of 10 filling the unsignaled section between the new CP EZLIABETH and the 125th St interlocking.

Now unsignaled track, even on commuter rail lines isn't that uncommon, but if one reviews the operating rules for that section you will not see anything pertaining to Track Warrant Control or even its lesser known GCOR cousin Track Permit Control. What one finds instead is Time Spacing, which is defined in a serious of special instructions in the METRA employee timetable.

* A proceed indication displayed by the controlled signals governing entrance to the non-signaled territory or verbal authority from the train dispatcher or control operator will authorize trains which have scheduled passenger stops, as indicated in the Employee Train Schedule, to enter and run with the current of traffic in the non-signaled territory. A train must not follow another train until 10 minutes after the preceding train has departed.
* Road Dispatcher at Gresham Junction and Control Operator at Blue Island must hold trains at the controlled signals governing entrance to the non-signaled territory of the Beverly Sub District until 10 minutes after the preceding train has passed. They must also notify any train which is followed by a train scheduled to precede it.
* Trains not indicated in the Employee Train Schedule as operating via the Beverly Sub District and trains moving against the current of traffic will be authorized by track permit after an absolute block has been established in advance of the movement.

What we have here is a somewhat informal version of timetable operation which keeps the time separation components, but discards many of the issues about actually keeping to your assigned schedule. Only scheduled trains may enter the time separation area on signal indication, but it doesn't matter what that schedule is or if they are following it. The rationale behind this the high density of stations which all trains on the line must stop at. With stations less than one half mile apart each there isn’t much room for trains to build up a dangerous amount of speed and it is not difficult to observe any traffic running on the line ahead.

Even with the frequent station stops and a 30 mph maximum line speed, a second layer of safety is provided by the operators (now dispatcher in the case of Gresham) who cannot display a signal into the time separation without waiting 10 minutes since any preceding train was admitted. This time separation requirement applies for trains within the block which cannot depart a station any time sooner than 10 minutes after the preceding train has departed. The signals at both entrances to the section can either display some version of Clear and Restricting, so just like in manual block systems the Clear served as a manual block proceed indication that is valid all the way to the next interlocking, unless the train is held up by the at station 10 minute rule. At the new CP-ELIZEBETH (replacing a portion of the old Gresham Junction interlocking) you can see the proper direction track westbound signal can display G/R on the upper head and R/L on the lower. The reverse track can display G/R/L on the lower head.

While in theory time separation could be employed equally well on a bi-directional scheme with admittance to the blocks governed by the operators/dispatchers at either end, in practice all reverse direction moves must get a track warrant. Moreover all non-scheduled trains must also get a track warrant as no scheduled train skips any stops and the station stops serve as safety critical time checks.

Unfortunately all these stops come at the cost of timeliness with the 5 miles in the un-signaled territory taking upwards of 20 minutes to traverse according to the schedule. That means that the line would not do much worse if it was simply converted to Yard Limits and trains run at restricted speed (although you might not be able to make any stops). In terms of train frequency the shortest headways on this line are 13-14 minutes apart, although to handle the peak traffic other trains can be sent via the Main Line with its full CTC protection.

In advance of each exit interlocking, CP-ELIZABETH to the east and 125th St to the west, there is an automatic distant signal allowing the block in advance of exit interlocking to be run under ABS rules. The setup is reminiscent of Amtrak style Rule 562 operation with cab signals with fixed waysides only at distant.

The history behind why this stretch of line was left signaled the way it was is a bit of a mystery, especially considering that the Rock Island was the first to make use of RTA funds to improve its service. One probably culprit are the large number of grade crossings in the Beverly Hills section of the line with 24 being located in the unsignaled section. Automatic crossing protection using DC track circuits would have required complex logic when combined with automatic block signaling. Demands from the time to improve crossing protection or an effort by the Rock Island to avoid paying crossing tenders may have lead to the discontinuance of automatic signaling in that area. The practice may have also evolved from older manual block or timetable operation that was never upgraded due to the slow speeds and frequent station stops.

How much longer this practice will continue is a matter for speculation. The Rock Island district is already targeted for a pilot PTC system and such dark territory is the thing that PTC generally eliminates as part of required signaling upgrades. However PTC could be used as an overlay to provide actual enforcement of the current time separation and remove any necessity for track circuits on this stretch of track. The time separation rules would of course probably be left in place for when the PTC system inevitably doesn't work.

METRA: Gresham Junction Tower

This is going to be the first in a series of inside looks at METRA interlocking towers in the Chicago area.  All of the behind the scenes photos that will be shown here were sent to me from an employee who had access to the towers in the time period 2006-2008 so don't go asking me how I was able to get into all these places.  However some of the sets will be interspersed with exterior shots that I have taken of the tower and/or interlocking.

Gresham Junction Tower, on Metra's Rock Island District commuter lines operating south of Chicago is a surprising survivor where conventional wisdom would have dictated its closure well before its actual demise on Jan 30th, 2010. The tower is also of special interest to the British signaling community because of the interlocking equipment installed within. For those of you who don't know, Gresham Junction housed unique Sequence Switch interlocking machine made by Standard Telephones and Cables Ltd of London. It was an NX design developed in the 1950's from Rotary system telephone exchange equipment. Not many were sold and Gresham Junction was the only unit installed in North America. The only other STC Sequence Switch interlockings anywhere in the world were two 1949 models installed in the old LNER boxes at Doncaster North and South and two improved models installed at Tollerton and Pilmoorin 1960 and 1961.

Gresham Junction is located at the northern split of the two Rock Island District sub-lines, which for lack of a proper name I will refer to as the Slow Line and the Fast Line. The Slow Line is used by most trains and has 11 stops between Gresham and Blue Island. The Fast Line is only used be a few rush hour express trains and has only two stops. Where the two lines re-join in the south there is the also still active Metra Blue Island tower, which has a more conventional NX board and is not to be confused with the more famous Blue Island tower nearby. As indicated by this line guide The Slow Line between Gresham Junction and Metra Blue Island is unsignaled, with trains operating under a Controlled Block system between the two interlockings. The Fast Line is signaled for bi-directional operation. In addition to the split Gresham Junction also handles a wye connection to an infrequently used connecting track that eventually winds up at the former US Steel plant in South Chicago near the famous Quad Draws at CP-509.

The tower is also unusual in that it is located such that a city street is between it and the Fast Line track it looks out on. In this photo we see the rear of the tower. The front can be covered by Google Street View. The tower has a typical slab side 50's design common to both towers in the Blue Island area.

Moving inside the tower we find a typical British green angled panel with some rather outsized NX knobs.Each knob had a number of possible route selections.  All the operator had to do was turn the knob to the desired route and press in.  To cancel a route the knob would be popped back out. While the interlocking is clearly oriented North/South, the tracks of the old Rock Island carry an East/West designation in the timetable, so operators have drawn a handy compass rose on the panel. The line heading east used to sport 3 tracks, but the topmost one is now just a stub. Yes, there is a bit of an odd bottleneck on both lines where trains in both directions must squeeze through a single path. You can see where another turnout used to be located between the eastward slow line track and main track 2 and also that there were 3 tracks in the west direction as well. The tower still supports a double slip switch that all slow line traffic must negotiate. Finally note the blocking tag on the entrance button to the Westward slow line, which is probably in place for the manual block protection.

On the right side of the panel we see more of the same including a second compass rose. The wye track used to have a controlled switch at its east point, but that is now hand operated.

Pulling back to a wider angle we see the photo probably dates sometime after 2006 given the date on the retirement plan announcement taped to the panel. The company issued 2003 calender is quite a bit out of date. In case of Nuclear War we can see that this tower is equipped with ample supplies of water and paper towels. While the panel has seen a typical number of "deletions" over the yeard, its interesting how much room there was on the "west" side of the board. I am unsure if there were plans to add more interlockings or signal the slow route, but I do not believe anything was ever removed from that section of the panel.

Moving into the locking room we find the guts of the interlocking in the form of sequence switches derived from telephone exchange technology. Sequence switches were developed by Bell Labs at as part of the common control equipment used in both rotary panel switches, with panel being adopted for the North American market, with rotary being sold in Europe.  An in depth explanation and demonstration of telecom sequence switches can be found courtesy of the Connections Museum in Seattle.

Here are selectors 1 through 5 and its astonishing how well maintained the equipment is. It is a testament to the original manufacturer and its subsequent maintainers that the equipment not only remains in service 50 years later, but also that it continues to look brand new. What is all the more astonishing is that the Rock Island railroad that built and owned the tower for its first 25 years was constantly going bankrupt.