A blog devoted to explaining the ins and outs of North American railroad signaling, past, present and future. This blog seeks to preserve through photo documentation the great diversity and technical ingenuity of 20th century signaling and interlocking hardware and technology. Related topics cover interlocking towers and railroad communications infrastructure.
Note, due to a web hosting failure some of the photos and links may be unavailable.
The SEPTA Broad Street Line is notable for being one of the best examples of pneumatically powered signaling appliances in the form of point machines and trip stops. The whole line is equipped with such devices except for the Fern Rock shop and yard complex, which was subjected to a re-signaling project around 2005. Well I just caught word that due to a long term plan to rebuild the City Hall station, SEPTA will be installing bi-directional signaling between the line's WALNUT and FAIRMOUNT interlockings.
Single direction signaling at WALNUT interlocking.
Since it was constructed in the late 1928 it has operated almost entirely with single direction ABS with a few isolated segments of bi-directional signaling within interlocking limits. SEPTA's plans to rebuild City Hall will take entire platforms out of service so the usual practice of closing either the local or express track will not be an option. As a result SEPTA is looking to install some bi-directional capability so the normally 4-track railroad can operate as a two track railroad between Walnut Locust and Girard stations.
It will be interesting to see what brand of signaling equipment SEPTA decides to go with and if they stick with pneumatic trip stops or convert to electric. After the MFL was re-signaled around 2000, SEPTA was able to bank a large amount of 1980's vintage pneumatic trips and A-10 point machines that have been slowly appearing on the BSL so there might be enough in stock to supply the project. Since the wayside signal system is likely to be replaced around when new rolling stock is purchased, this would save money on an ultimately short term change. On the other hand if someone else is paying, SEPTA could decide to rid themselves of a "troublesome" technology. There could also be a mix with the existing equipment left alone and only the new reverse direction signals getting electric. Regardless, I think I might take the time to get photos of whatever is currently in place.
You might have missed it due to COVID news coverage, but back in January 2020, whomever it is that runs BART decided to use some new taxpayer funding to replace the "50 year old" audio frequency cab signal system with CBTC. While BART does indeed have some extreme capacity constraints funneling 4 lines down a two track trunk between Oakland and Southern San Francisco, as that very city has seen with its MUNI Metro Subway, CBTC is not all its tracked up to be.
This is being brought to you by the same team that sold a $400 million combination railcar and re-signaling package to the Baltimore Metro. Hitachi purchased the Italian railcar manufacturer Breda and the Italian signal provider Ansaldo, which itself was the parent of Union Switch and Signal. I guess because Hitachi figured that Japanese engineering was better than that of Italy it has gone in with a full re-branding even though I doubt any of the actual work is being carried out in Japan. Like the DC Metro, BART has a core system that is approaching 50 years in age and likely was looking at a full signal equipment replacement similar to that which WMATA carried out after the 2009 signaling related collision. Although BART has seen many expansions over the years, its core system was and likely still is based on GRS relays and Wee-Zee bond technology.
While BART may be hoping for those 30 trains per hour, the reality will likely be less as at a certain point trains become dwell time limited. It's not that passengers can't all shuffle on and off in 30 seconds, its that they will likely not do it reliably and even a small disruption at peak capacity will result a standing wave traffic jam. Hopefully, because Bay Area, there will be some sort of backup system as you know every wanna be hacker looking to make a name for themselves will be looking for ways to disrupt the system and anything that uses wireless is ripe for disruption. If cab signal circuits will remain in service as a backup or on outer portions of the system where such equipment is not life expired, remains to be seen. The BART system was already pretty useless to railfan with dull signals and rolling stock hostile to look ahead or behind views. The new D type cars were posed to reverse this trend so get your photos and videos of the current signaling and train control before it vanishes.
Communications Based Train Control promises higher capacity at lower costs thanks to the magic of WIRELESS TECHNOLOGY! However almost every real world situation that makes use of it seems to wind up costing a ridiculous amount, having major reliability problems or both. It turns out that with signaling there is no free lunch, but when faced with overcrowded subway trains, planners can't help but get seduced by those lovely braking curved. I mean fixed block, that's so 1890, surely we can do better!
In 2016 the MBTA was conducting a capacity study for the Red Line, which currently has a somewhat anemic throughput of 13tph in the peak period. With new rolling stock on order, the (T) would literally have more cars than it could run. The current signaling system made use of fix block audio frequency cab signals installed in the 1980's. This is similar to many other transit systems such as the CTA, WMATA and BART. Of course CTBC is the to go technology for capacity expansion and the study quickly confirmed this. Oh wait, it didn't.
• A detailed analysis assuming a moving
block CBTC system on the Red Line was completed.
• Analysis found that a CBTC system would produce
an improvement of just one train per hour beyond
the improvement from the new cars and minor
system changes.
• Major Red Line capacity improvements can be
achieved without implementing very costly CBTC.
• Long dwell times in the downtown area and close
spacing of stations limit CBTC as much as they
limit fixed block systems.
That's right, just like the costly NYC Subway L Train CBTC system only increased capacity by 2 trains per hour, applying CTBC to the Red Line would only improve capacity by 1 train per hour over a fixed block alternative. Past a certain threshold capacity is limited by dwell time and the efficiency of terminal interlockings. The study also found...
• The shorter the block length, the closer the
system is to the ideal CBTC (moving block)
braking distance
• MBTA block lengths in the central subway already
average less than 500 feet (6 car trains are 416
feet long)
It's nice to see that for once a transit agency actually ran the numbers and decided that CBTC just wasn't worth it. It turned out the best way to increase the capacity was simply to allow the new rolling stock to use updated braking curves that will result in later braking and more aggressive cab signal speed stepdowns. Also the 1980's audio frequency cab signal system will have its components replaced with digital versions that have faster reaction time and thus allowances for less conservative block progression.
The Londonist has just produced a very interesting piece on the LUL Edgware Road signal cabin, which was built in 1926 with a Westinghouse Style K interlocking machine (license built UK version of a US&S Model 14). Unfortunately the London Underground has been bitten by the same CTBC bug as the NYC Subway, despite the old adage "If it ain't broke, don't fix it". The article comes with an attached video and numerous photos of the signal cabin and a number of other cabins also at risk for closure. Because putting one's eggs in one basket is all the rage, the LUL will also be converting to a centralized control center model.
The good news is that there are plans to preserve the cabin, although the ultimate level of interactivity or public access remains unclear. Here is another video showing a compressed view of an entire night shift at the cabin.
Just a quick status update from the Queens Boulevard Line in NYC. As I previously reported, the NYCTA was closing towers along the line as part of a general move away from manual interlocking operation on the IND division. At that time Roosevelt Ave tower has closed with Continental Ave and Union Turnpike close behind.
Gone without a trace
Well as of Veterans Day there has been some good news and bad news. The bad news is that not only have Roosevelt and Continental both closed, but both classic interlocking machines, a GRS Model 5 and US&S Model 14, have both been removed and the spaced converted into employee hangouts. The good news is that Union Turnpike is still in operation along with the small tower at Northern Boulevard on the local branch of the line. That small tower operates a single trailing point crossover with a 12-lever GRS Model 5 machine.
In related news, color light dwarf signals continued to appear in the JAY interlocking complex on the LIRR, one even being at the end of a platform. As mentioned previously they are bare stacks of Safetran clam shells instead of something sensible like an LED searchlight.
DUNTON interlocking is so far unaffected and both VAN and BROOK interlockings are also not exhibiting any changes. The temporary pedestal automatic signals are still in place at Woodside and I recommend anyone in the area try to get out and photograph them before the new color light signal bridge is activated for the East Side Access project. One upcoming opportunity will be for this year's Holiday Nostalgia Train, which will be providing runs between 2nd Ave and 95th St on the Second Avenue Subway instead of to Queens Plaza. I highly recommend it!
Some of you may have heard that the Baltimore Metro was installing a new CBTC signaling system in conjunction with its new order of 78 Breda (now owned by Hitachi) railcars. This might be surprising as such systems tend to only be economically viable when extremely high throughput over 20tph is required. Baltimore's 6tph service is more than adequately serviced by a traditional block system, but I figured that once again some non-technical administrator was fooled by a signal vendor. However this weekend I learned that the situation is far worse. Not only has the Maryland MTA guppied up for CBTC, but they have also opted to adopt a German style axle counter system for backup train detection without any track circuits, even within interlockings.
The Baltimore metro was constructed back in 1983 with a fairly typical audio frequency cab signal system with 6 speed codes. Apparently they have not very little investment in renewing the system and 30 years later most of the impedance bonds are end of life and getting unreliable so they see an axle counter system as a way to cut costs. Breda is under the same umbrella as Ansaldo STS, the Italian signaling company that bought US&S and now both operate under Hitachi. This enabled Hitachi to offer both the cars and signal system as a $400 million package deal, and Baltimore found it hard to say no.
Unfortunately use of a German style signal system without positive train detection may result in problems when the German railway culture is not important. The Baltimore Metro will be blind to broken rails, floods and random vehicles rolling onto the main line. Track workers will no longer be able to clip in a track circuit shunt to protect themselves. In Germany the government spends freely on rail maintenance and employees tend to obey orders without question. In the lower cost United States, it is only a matter of time before this budget system proves deadly.
I just found a few interesting videos involving UK signalboxes. The first two involve the Banbury North Signalbox , which was recently decommissioned, but then opened for public tours (a somewhat rare occurrence due to all the health and safety BS their railways are tied up in). Unfortunately the signalbox, like many others, is slated for eventual demolition so little other purpose than it being there. Britain's attitude towards its decommissioned signalboxes is downright baffling seeing as every foot of railway infrastructure is publicly owned and almost everything in the UK is covered by some sort of historic preservation law. Network Rail also seems to be chronically pressed for cash and where they can find the funds for these demolitions is beyond me.
The first video shows the full tour that was given to the public and the second video shows the view from the locking room as the levers are manipulated. Those of your from North America should keep in mind that mechanical British signalboxes such as this, typically work on the manual block system. Some track circuits may be provided, but train movement is primarily by manual block using block instruments instead of voice or message communications.
The third video is from Harrow On The Hill signal cabin on the London Underground in 2002 and shows a Westinghouse Style N machine, which is basically a US&S Model 14 with the levers pivoted around 90 degrees so that they throw in the traditional "back and forth" orientation, instead of left and right. Even the tri-positionality of some of the signal levers is retained. The most fascinating thing about this video is the use of a pneumatic assist to move levers at the far end of the frame when certain route levers are pulled in the primary operating area. It's basically a non-vital intra-tower remote control system that doesn't require additional relay logic, a serious expense in pre and post war Briton. This technology was later extended to create the Style V frame where all the levers were moved primarily by remote control pneumatics.
BTW, if you are wondering why the model board is all lit it, is it because that was considered safety critical information and any bulb out had to mark the track circuit as "occupied". Of course with the bulbs burning by default I am sure there would be plenty of bulb out opportunities.
In the heyday of North American railroad signaling railroads and transit systems alike were in either the US&S Camp or the GRS Camp, although a brave few sometimes split their orders. Well it turns out that the abandoned Springfield Subway system was in the former as evidenced by this screen capture from the 14th episode of the 21st season of The Simpsons entitled Postcards from the Wedge. In this episode Bart commandeers a train in the disused Springfield Subway and Homer manages to save him by running into the subway control room and pulling a large and conveniently labeled "Kill Switch." Well, what else appears in the background but an animated US&S Model 14 interlocking machine!!
I'm serious, check it out.
Of all the nit picky technical things I would have picked for The Simpsons to get RIGHT in an episode this probably would have been near the bottom of my list. The mechanics of how this happens is not completely hard to guess at however, The subway system in New York, a well known source of comedic writing and animation talent, has a number of "fishbowl towers" on the IND division where old interlocking machines such as the Model 14 shown are visible to anyone standing around on the platform. The most access able of the Model 14 towers are in Queens, like this example at Union Turnpike, although I have been told one can see into Jay St in Brooklyn as well.
I have just become aware that the last Main Line interlocking tower on the entire IRT located at East 180th St on the White Plains Road Line has been closed and demolished. Built in 1912, E180th St tower stood for 99 years at what became the junction of the Dyre Ave Line shuttling trains in and out of the three track station and E18th St Yard.
E180th St 2011
E180th St 1912
While all the other single interlocking towers on the IRT were closed in the 1950's and 60's to make way for extensive "Panel" type Master Towers, E180th St had survived due in part to its complexity and late model 79 lever US&S Model 14 machine,which would have been much newer than the original IRT signaling.
Later being assigned a US&S UR style NX machine for the Dyre Line, E180th St only lost its semaphore signals in the early 1970's and later the interlocking became the final holdout for the old style IRT route signaling where each complete signal head represented a route. This resulted in such unique signal indications as R/G/R and G/R for nearly a decade after it had vanished on all other parts of the NYC Subway.
