Retrotechtacular: Upgrading Train Signaling Before The Information Age


What’s surprising about the subject of this week’s Retrotechtacular is that the subject is not from that long ago. But looking at the way in which the work was done makes it feel so far in the past. In 1974 the British Railways Board set out to modernize and interconnect the signaling system. What you see above is one of hundreds of old signal control houses slated to be replaced by an interconnected system.

These days we take this sort of thing for granted. But from the start of the project it’s clear how the technology available at the time limited the efficiency of the development process. We’re not talking about all of the electro-mechanical parts shown during the manufacturing part of the video. Nope, right off the bat the volumes of large-format paper schematics and logic diagrams seem daunting. Rooms full of engineers with stacks of bound planning documents feel alien to us since these days even having to print out a boarding pass seems antiquated.

With fantastic half-hour videos like this one available who needs television? We’d recommend adding this to your watch list so you can properly enjoy it. They show off everything; manufacturing the cables, stringing them between the signal towers, assembling the control panels, testing, and much more.

[Thanks Stefan]

Retrotechtacular is a weekly column featuring hacks, technology, and kitsch from ages of yore. Help keep it fresh by sending in your ideas for future installments.

25 thoughts on “Retrotechtacular: Upgrading Train Signaling Before The Information Age

  1. As a former control systems engineer, I found it fascinating to see how much has changed in the last 40 years…and how much has not.

    Mimic Panels are still very common today, even though graphical interfaces on computer monitors have taken much of the role. When you have a single static display, everyone can see it at once and analyze at a glance–that’s really important when you’re dealing with abnormal situations. Relay logic is still fairly common in industrial control systems, particularly electrical systems–it works, it’s easy to diagnose, and with more modern manufacturing methods, hermetically sealed relays are dead reliable. Relays can’t be hacked by some guy halfway around the world. And they have a break-before-make design, so you can ensure through *hardware* that two incompatible conditions can’t happen at the same time.

    I found it interesting that they used mechanical buzzers rather than LC filters in the frequency division multiplexing. It seems to me that a no-moving-parts filter would have reliability and cost advantages over what is effectively a tuned solenoid.

    1. LC filters built using the electronics of the era would have too much drift and not enough selectivity. A mechanical resonator can be more easily built temperature stable, like clock pendulums that are made with different metals pre-tensioned to have the thermal expansions cancel out.

    1. Yup, so much industry gone buh-bye from the UK and USA. Sad that nobody in the UK could roll the boiler sheeting for that new Tornado steam engine. Had to farm it out to a German company!

      1. The US manufacturing output was never higher in previous decades than in this one. It has more than doubled since 1975. China has only surpassed it a couple of years ago.

        It took a toll during the recession, but it’s still on the top two.

  2. love it. slightly side stepping but in the video there were two trains transporting cars, never see that these days, its all done by road, bit of a shame, aside from some heavy industry most seems to be passenger travel. In my misspent youth i played in a few of the relay rooms / signal boxes around glasgow, they were derelict then and most are gone now. amasing the rate technology progresses and how “wasted” all the effort in that video seems compared to modern equipment.

    1. Cars might go on truck from an “inland port” to a dealership, but from the coast to the inland ports, they go by the heavy rail lines. Maybe OP is just nearer one of the big commuter lines on the coast, but the bulk of weight that passes by here and where I grew up is all freight.

  3. Does anyone know what the expected longevity was for this project? They mentioned some systems being retired that had been in service since the sixties, which would be only 14 years or less at the time. How long did they expect this system to operate? Also, any idea about the computer language used for the digital side?

    1. I posted this to a UK railway newsgroup. According to one of the signalling engineers, most of this installation is still there, still handling traffic day-in day-out on one of the most critical lines in the country. There’s a plan to replace signalling on the West Coast Mainline with ERTMS (computer-based cab signalling) by 2030, so looks unlikely there will be major changes before then.

      1. Thank you for checking. That is very impressive. Perhaps we need to think of our electronic technology a little more like our architecture and design long-term more often, but, I suppose, like all things electronic technology also has to respond to the market, etc.

  4. Interestingly, railway signalling and switching was the incentive for the development of queuing theory. And a very strong incentive it is. Having two trains trying to use the same track at the same time is a lot more traumatic than having two processes trying to use the same memory location.

  5. I find it odd, that in this day and age in the USA, a project like this would be derided as a “make-work program that ends up depriving honest blue collar trackmen their jobs when it’s done” instead of something that would make the rails easier to use. Not that our rails need a digital upgrade, but I think the metaphor stands.

    And compared to the CCC program during the depression, a program of similar nature would be a shot in the arm for the economy and for the under employed. And it would never happen.

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