The Island Gardens Accident: What Really Happened

So just how did a train end up hanging off the end of a viaduct in Millwall in 1987? Time for a closer look.
The Island Gardens video: • Island Gardens and Nor...
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[@DigitalDiabloUK]

As someone involved in the IT industry for 25years, I’ve learned that if you invent a foolproof system, a better fool will be along shortly.

[@henrybest4057]

A better fool!!! Don't you mean a fully qualified fool? There's nothing 'better' about being a fool.

[@Satters]

in Post Office engineering it was accepted nothing is foolproof and everything breaks eventually, today electronics fail more frequently, yet subscribers expectation is for greater longevity and reliability

[@highpath4776]

I need to comment on the Microsoft Developer Channel. I had MS Exchange I think on my PC I was using to process my emails. It had an option to change the Inbox, etc , location, So I moved all the .?bx files to the new location, then told MS Exchange where the new location was. Instead of changing its internal pointers it created new (without checking) inboxes and so on, in the new drive/folder overwriting the data in the filenames (meaning a recovery program would not work ), with null new files, then , because I had moved the files beforehand, could not populate the new location with the original data (and yes , I had not made a back up, AND my ISP had managed to loose all the mailbox information too owing to an 'upgrade' the same weekend, AND my spare PC - at my in laws, developed a physical hardware fault on the disk drive so windows would not load (normally I would have brought the drive back by the in-laws took it in to be repaired - the company replaced the hard drive, but did not look to see it had been physically and logically partioned and did not copy over the DATA section of the disk , which was OK, and binned the disc.

[@BertGrink]

Dear Customers! We are happy to announce that Fool V2.0 is now available for all users. Furthermore, we can also reveal at this point that we have begun working on Fool V2.5, as we are sure it will be a necessary upgrade in the near future.

[@tlillis4]

I believe it was Douglas Adams who said “A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools.” I left the IT industry after 25 years: too many fools. The only problem now is to find someone who wants a 55 year old intern. 😀

[@roblyndon5267]

If I miss anything about London life, it's the Driving the DLR game. The art is to combine nonchalance and apparent disinterest with extreme aggression and ruthlessness.

[@bigblue6917]

Or, as it's known, being a passenger

[@caramelldansen2204]

"Driving the DLR" is a game where you pretend you have a steering wheel and make race car noises with your mouth when you're at the front

[@ssbohio]

So much of life is "to combine nonchalance and apparent disinterest with extreme aggression and ruthlessness," isn't it?

[@qwertyTRiG]

The other trick may be to have a child with you. I'm certain that my dad made use of having us with him to get to the front himself sometimes.

[@trevordance5181]

Reminds me of the time when I saw a dad with a small child pushing his way to the front seat. "Let's pretend we're driving", he said and then started making noises and moving invisible levers and controls with his hands. "Isn't this fun", he exclaimed to the completely disinterested child. It was obvious to all present that the child was merely a prop to let him indulge publically in his train driving fantasies without, in his mind at least, being regarded as an overgrown schoolkid.

[@YellowPinkie]

This is why you test. This is where you learn the most.

[@ashleigh.]

♬ For the good of all of us... ♬

[@AnthonyHandcock]

Yep... If you are testing something that wasn't working you want it to work. If you're testing something was working you want it to fail. Admittedly that's stretching the definition of the word "want" way beyond any reasonable breaking point but it is effectively the whole point of testing... To be proven wrong if you are.

[@simonrussell4986]

Absolutely. You learn more from mistakes. Granted, it's an expensive mistake, but it saved a lot.

[@sumpyman]

Testing at the end of the line with a vertical drop was a good idea then? 🤣

[@sumpyman]

@@creamwobbly No. But testing at another station with some 'just in case track' would of been less risky!

[@MrGreatplum]

This is the best “apology” video I’ve seen on KZbin! This is excellent technical geekiness we all need and want!

[@JagoHazzard]

Many thanks!

[@MirzaAhmed89]

I see it as more of a "clarification" video.

[@MrGreatplum]

@@MirzaAhmed89 - that might have been the word I was searching for at 8am this morning!

[@reuben8140]

CGP Grey’s “I was wrong” was spectacular too

[@LewisCollard]

As someone whose day job is in software...as soon as you said the word "asynchronous" I immediately thought "oh no, it's going to be a race condition or timing bug isn't it?" and I wasn't far off. Awesome video my man. Always love your microhistories but this might be your best yet!

[@Stettafire]

Async programming is always "fun"

[@smorrisby]

That's exactly what I thought. A timing issue was inevitable. However it's easy to be wise after the event with crystal clear hindsight.

[@PhonyBread]

As soon as I heard '1 second processing loop' I knew what went wrong...

[@paulhaynes8045]

Reliant on three unsynchronized computers, and 0.2 second safety margin - it's like saying of course we can keep the marches in the same box as the fireworks - what can possibly go wrong...

[@EtwasMartin]

And here is why you are a great youtuber: you are willing to correct yourself if the new information comes from a valid source. Great job on claryfing this.

[@JagoHazzard]

Thanks!

[@SecretSquirrelFun]

Very appropriately described as a “loophole” given the 3 computers and their individual one second loops!!

[@DJTrainBrain]

It did sound as if Jago missed his unintended pun, though... :-)

[@tomasjones3755]

Yeah - I caught that 'loophole' bit, as well; textbook definition, to be sure.

[@mkendallpk4321]

I think the computers were a little loopy.

[@ShaunieDale]

This is what interrupts are for. "Stop what you are doing and listen right now, this is important!"

[@stephenhunter70]

@@ShaunieDale Maybe the tech was "interrupted" just before entering the relevant script into the software. Oh dear.

[@ssbohio]

A word in your shell-like: Be aware that "lighthouse keeping" is an entirely different job from "light housekeeping." I almost became a light housekeeper through that mistake.

[@davidbull7210]

Graeme Garden made that mistake...

[@2H80vids]

That's been used a few times on tv; was it not used on Dinner Ladies and, I think Only Fools and Horses?

[@twotone3070]

Yeah, uniforms are totally different.

[@EscapeMCP]

With lighthouses and housework, there's a four candles joke in here somewhere.

[@CurmudgeonExtraordinaire]

And there is a big difference in a "chicken ranch" vs a "chicken farm"... The former will most likely get you into legal trouble... :)

[@sandwich2473]

Big respect to Jim for coming forward and lending you his expertise on the subject. It really is wonderful that your audience has within it, some very experienced people in the subjects that you will sometimes cover. I have to commend you for making this video. I know a lot of other people wouldn't have done the same thing. It's really interesting to see what really happened with it All very well done

[@MatthewJohnCrittenden]

As a software engineer of many years I can see exactly how this happens, great explanation. This would all be virtually modelled these days, a bit extreme to test an edge case in the real world though!

[@57thorns]

Or at least test it with plenty of safety track instead of the end of the line behind it. The test would be something like going at overspeed and checking how long it takes to stop the train. Unfortunately I wish I could say that people would understand that 1+1+1>2.7 and that a design like that is not good enough, but I expect that kind of problem exists in many newer systems as well.

[@hosedevil]

Yeah, but it was in the '80s, less elf and safety, and also not the first time something like this had happened.

[@DanielsPolitics1]

It is entirely normal in railway safety to fully test safety critical edge cases.

[@gormster]

The idea of a fixed *one second* loop seems heinously long to me here in the 21st century. But I’ve never had to design absolutely-cannot-fail systems like these, so maybe it’s less ridiculous than it sounds at first blush.

[@RobertThz]

@@gormster Fixed timing loops are in fact fairly common in safety critical systems, since it makes it much easier to formally analyse the design for correctness and worst response time. Pity that it wasn't done here.

[@davidbull7210]

I bet the DLR's mother called it by its full name that night when it got home...

[@bigblue6917]

That always sounds worse with Russian names. And even worse then that it's not just your mum who does it. Everyone gets a chance to have a go.

[@kanedaku]

DOCKLANDS LIGHT RAILWAY WHAT TIME DO YOU CALL THIS?

[@robmarkworth5377]

JAMES PETER DOCKLANDS LIGHT RAILWAY SMITH what on EARTH do you think you're doing?!

[@davidbull7210]

@@robmarkworth5377 ALEXANDER DOCKLANDS ILYICH LIGHT KONSTANTINE RAILWAY! You have overshot the mark and brought shame to mamma!

[@bigblue6917]

@@davidbull7210 Some said he was not going to fast. Others said he was Rushin

[@chuckboyle8456]

Very interesting episode, nicely done...thanks Jago. You have given us a new phrase for the lexicon...”latency in message processing”. I will be using it the next time my wife instructs me to Hoover the flat before supper!

[@RogueWJL]

I can confirm I have never stood on any DLR station desperate to gain the front seats if the opportunity arises, on a train. I can confirm I have never shoved past some old dear in a desperate attempt to get said seats nor sat the rest of the journey fearful of turning around and seeing a sea of disapproving faces. Great video

[@tinabolesful5184]

Oh it was you

[@jpr455]

Very interesting story. As computer programmer myself its nice to know that they did such thorough testing. It's actually worrying when you test and nothing goes wrong, you start wondering what you missed. :) I don't even live in London, but I love your videos

[@paulhaynes8045]

Except that the test that actually revealed the error wasn't part of the 'thorough testing', it was a very lucky unscheduled extra. If they'd stuck to the programme, the first time this problem would have been revealed would have been the day that a DLR train hit the buffers!

[@JanRademan]

Just another buffer overrun.

[@ranulfdoswell]

Best comment so far! :D

[@maninacave]

Brilliant!!

[@brucewilliams8714]

I'm glad I wasn't there. I'm an old buffer.

[@ssbohio]

Involving both a physical buffer and a computer buffer.

[@bobfountain2959]

Very witty! I’d be proud of that comment.

[@shrikelet]

This was a really interesting episode. It raises- in my mind at least- interesting moral questions of the interface between engineering and bureaucracy. Kudos to Jim for bringing it to light, and kudos to Jago for having the intestinal fortitude to break policy in order to get this story out there.

[@susiewickham9990]

Good explanation. I didn’t get confused once 😀.

[@Outfrost]

As a software engineer, I really appreciate the technical explanation. It's always series of small details like these, lining up to create scenarios noone might've thought of. Whenever I find one of them in something I'm working on, and figure out what caused it, I feel a great sense of satisfaction, and I reckon I'm not alone in that :) We've just destroyed a testing database, or the undercarriage of a DLR unit, sure, but we get to fix it before going live, and have just saved ourselves a humongous headache later on.

[@slim5782]

Thanks for including the technical information. As a programmer it's very clear.

[@HunterRodrigez]

After the crash: "Are we in trouble now? we did an unauthorized test and crashed one of the trains but we also found a huge safety issue... so are we heros or are we about to lose our jobs and possibly get sued?"

[@GustavSvard]

I know the SecOps team at my job would come over with a big bag of candy if anyone caught a safety issue like that. /or: they'd be amazed how anything we did could ever create a safety issue like that considering it's backend stuff for websites.

[@seraphina985]

@@GustavSvard It's certainly possible depending on the data the site is processing, internet services are certainly used by other systems and personnel to make decisions that are safety-critical. An error in the information provided by those sorts of systems could lead to fatal errors.

[@MsGrandunion]

Thank you for not being a lighthouse keeper. Expat Londoner here, (who can no longer stand casually at Bank and then shove my way to the front), your videos are a wonderful solution to homesickness!

[@stevebluesbury6206]

What a blooming brilliant video. Clears up the obfuscation of ‘official sources’ and in a typically Jagoistic way. Don’t think of it as a correction; more of an expansion of the tale... from the DLR. 😃

[@chrisroberts2266]

People often seem to miss the main point of testing is that it is ok for things to go wrong (and often encouraged), so they don't after release of your product. In this case the momentum of a fully laden train may have caused the braking distance to increase and mean that the front carriage may have gone all the way over! Big thank you to Jim for explaining the process! and to you Jago for making fantastic videos!

[@jeantremlett174]

Thanks Jago for making an exception and to Jim for his very understandable explanation.

[@yabbaso]

I'll be sharing this with my A-Level Comp Sci classes :) this is brilliant Jago!

[@JagoHazzard]

Thanks!

[@TransportationTravels]

You learn more from mistakes and things going wrong than when things go right. Thanks for producing this excellent video!

[@jlewis997]

Been in the rail industry 25 years and it's interesting to see the technical side of the test procedure

[@Aengus42]

This is what the internet excels at! The free flow of information that used to just become known via the "I met a guy in the pub last night..." network. Please thank him for us Jago!

[@Leonard_Smith]

The content gets better and better. The presentation hits the mark every time. Where will it all end?

[@stevengrice3105]

Always enjoyable to understand the real reason for stuff going wrong. Life if full of stuff not going to plan, and very happy to DLR looking after passenger interests. Thanks for the video.

[@user-pw3tr1xg2x]

Thanks for the video Jago.

[@stevenflebbe]

Accidents that happen because of situations no one anticipated can be perplexing, to say the least. There were two of those when I worked in the Safety Department of the Chicago Transit Authority. One in 2013 which was referred to as the "ghost train"...which involved water getting in to control cables, causing shorts which overrode "deadman" circuitry and allowed the train to move without an operator. The other was the 2014 derailment at O'Hare terminal...which involved insufficient placement of emergency track trips to stop a train traveling at unanticipated speed as it entered the terminal. There were instances of human error and other factors leading up to the incident in both cases, but the ultimate results...a train running without an operator and another train crashing through the bumper at the end of the track were both from unanticipated causes.

[@Sparkle_Fox]

Seeing a new Jago video in the mornings makes waking up not so bad.. Also hey 100K! 🎆

[@ManlykefreshINC]

You are the man. I wish a lot more KZbinrs were more like you To make it even more interesting you added humour and wit to this video 👏🏾👏🏾👏🏾👍🏾👍🏾

[@philiphowley4243]

Can you imagine the sort of testing NASA must get into? A great explanation, very clearly expressed.

[@57thorns]

I can, the same for anything flight related inside the athmospehere.

[@ReklawUK]

That train nearly became a flight....

[@highpath4776]

Hmm, like rockets and programs that a calibrated in the wrong dimensions (m instead of mm for example, or squashed O rings).

[@paulhaynes8045]

@@highpath4776 or a known safety problem (it being too cold for flying or lumps of insulation falling off on every flight) being ignored by management...

[@Peasmouldia]

That sitting up front was a thing on the old "heritage" BR DMUs. Some less sociable drivers would pull the blinds down to thwart the railbasher sitting behind him.. Thanks JH.

[@thomasm1964]

As a kid, I once overnighted (involuntarily) at Shrewsbury station. The station staff kept an avuncular eye on me and found out I wanted to go to Ludlow. Early in the morning, I was invited into the stationmaster’s office, given a mug of proper railwayman’s tea (hot, strong, milky and very sweet), asked if I had a ticket (which wasn’t checked) and put on the parcels train to Ludlow - in the cab with the driver! What a great journey! I can still remember the cows and horses in the fields swathed in pink mist, the oncoming trains making me jump every few minutes and the kindness of the entire railway staff over the course of that night and morning. A very happy day!

[@Peasmouldia]

@@thomasm1964 Back in the 80s my wife and I used to take an early morning DMU from Melksham to Weymouth. It started from Cardiff Canton depot and delivered sets for other diagrams. The Cardiff drivers were really nice and we would sit at the front, only passengers on the train, while they would tell us about their railway, and sometimes personal lives. Real shame that KZbin came along a little to late to record their experiences. Thanks for sharing. Nice.

[@fenlinescouser3898]

@@thomasm1964 I wonder how often this happened. I had an uncle doing his National Service and returning to Ludlow for Xmas leave. With poor connections and late running he arrived at Hereford way after the last departure of the day. Enquiring of the sole staff member he could find what time the first train departed the next morning the chap arranged for the next mixed freight to be held at the platform and following conversation with train crew and guard he was accommodated in the brake van. Not the smoothest of rides, reportedly, but good company, digestives and hot tea from the billy atop the stove.

[@AtheistOrphan]

Being the son of a railwayman, my father would often ask the driver if I could ride up front when I was a nipper.

[@uk-martin4905]

Happy memories of having the most-prized seat at the front of a magnificent 'heritage' class 105 DMU from North Woolwich to Camden Road in, I think, the summer of 1981. As a former B.R. South Suburban Electrics south-east Londoner for the first 20 years of my life, my joy was unconfined (some masterful understatement there) as I experienced the sounds of the rather aggressively- driven DMU on the service that had been introduced by the Greater London Council a few weeks earlier. Happy days!

[@Damsjov]

Congratulations on 100k subs! Keep up the good work :)

[@ricktownend9144]

If this explains in a nutshell why Crossrail is taking so long, then it will probably have been worth the wait...

[@bfapple]

Software testing is very very time consuming.

[@user-de4cq6uk6l]

Yep, signaling testing is one of the major things taking time. I’d rather wait another year for it to open then get into an underground train crash due to a signaling error

[@ubergeekian]

@@user-de4cq6uk6l Still, it will be worth it if "signalling" is ever to be installed on another railway. Pioneering is hard.

[@andreww2098]

@@bfapple unless you are a games company then you rely on end user testing (mutter, mutter, Bethesda!)

[@smeghead7698]

@@andreww2098 I'm still waiting for a cheque from R* for beta testing rdr2 for them.

[@prof.hectorholbrook4692]

Very good. Well explained. The incident was indeed a precious test in terms of Risk Analysis & QRA in a typical "Test & Trial" environment in the railway safety arena (authorised or not!).

[@bigblue6917]

Well if your going to have an accident it's best done during testing. I used to be a lighthouse keeper but I was fired for what they said was 'safety reasons.' They said I was unsafe just because I could not sleep with the light on.

[@handyandy6050]

I bought a lighthouse with a view to doing it up as a "quirky" place to live. It's been an "on and off" project for years.

[@dangerousandy]

Superb! Really enjoyed this. It’s a good job that they didn’t just sign off on six tests. I have just finished reading an accident report (exciting life I lead...) into the rail crash at Wigan in February 1984. As you state in your video, accidents occur due to unusual circumstances adding up, and that is exactly what happened in this case, unfortunately claiming two lives in the process.

[@McMetro]

Congratulations on 100,000 Subscribers! 🎉 😃

[@PtolemyJones]

I would love to see you do videos about being a lighthouse keeper, I imagine they would be wonderful.

[@vincenthuying98]

Marvelously enlightened video on a subject which doesn’t seem light after having been taken along the delay in the atp by which this video came to fruition. Overall the delays in atp’s, or atb’s in other languages, have been found to be the cause of inconsistencies at low speeds. So, in this special case a many thanks for explaining this ‘light’ problem into such detail.

[@highpath4776]

So at a speed slower than a clock cycle or whatever the parameters can fit more than once into the expected slot , the over-run at the edge of the cycle is wrongly detected ?

[@vincenthuying98]

@@highpath4776something like that is the gist of the flaw as it existed in atp’s, atb’s. As far as I’m aware it can even occur in older block detection for model railroads, however, the mass of those trains induces an almost immediate stop. Not so for real trains whose travel of brake is something systems should always anticipate on.

[@thomasm1964]

Very clear explanation of the computing issues there!

[@mattscudder1975]

One of the things I love about your clips Jago, other than the trains, models, sarcasm and humour, is that I know what I’m going to get and the repetition is part of that. I am of course referring to your use of the word video at the start. I’m know wondering how many times you could get away with saying the same word in one sentence as well as one clip? 😂😂😂

[@highpath4776]

Many , Many , Many times, I guess.

[@iankemp1131]

The old punctuation test: John, where James had had had had had had had had had had had the teacher's approval. Which becomes: "John, where James had had "had", had had "had had". "Had had" had had the teacher's approval.

[@tw25rw]

I used to catch the DLR to/from Elverson Rd every day for 10 years. Thanks for showing footage of that route.

[@PtolemyJones]

Wow, that was fascinating. How interesting. They were indeed lucky to get that result when they did, could have been seriously tragic. Thank you Jim.

[@sewing9434]

Thanks to you (and Jim!) for another fascinating and educational video. It sounds like their rigorous testing was a "successful failure": something they could learn and improve from! And congrats on making it to 100K subscribers!

[@mh8265]

Excellent video and it reminded me of the Therac-25 accidents and how timing was everything in a safety critical system, unfortunately, there was more complacency from the supplier.

[@pmberry]

Of course the Therac was never properly designed, documented or tested before release into the real world. The DLR was.

[@GregBakker]

Really neat video, thanks for putting it up. Interesting case study for system design.

[@mikayla9146]

Thanks for the info. Always a pleasure to watch.🙂

[@johnburns4017]

The train was under *test.* Many *tests* have no success or failure, only a result to be analysed.

[@clickrick]

There is a school of thought which considers a test which achieves its normal output for normal inputs to be a failure, and only those from which you learn something new to be a success. I see where they're coming from, though I don't entirely agree with it as a position. Regression tests, for example, are meant to check for normal results given normal inputs even after some change has been made in the system.

[@johnburns4017]

@@clickrick There are many different types of tests, with different parameters. One is a big machine pulling at bolts to snap them. The bolt has a range of strength for its application. If it snaps well above the specified strength, then the test is a _success._ Open ended test(s) are different. Test something to see how it performs way above its specification or intended use, then analyse. In this train application, a test would be to saturate the control system to see how it performs. The tester would regard a _failure_ of the equipment as a _success._ He found a problem.

[@sumpyman]

Was undertaking the test at the end of the line with a 10 metre drop, a successful outcome of a failure to plan?

[@johnburns4017]

@@sumpyman That test lacked a safety margin.

[@sumpyman]

@@johnburns4017 And safety margins are very important parts of a test. Therefore the test was a failure. If they had performed the test one station back, then the outcome would have been a success. Same learnings, no embarrassment, no extra costs and no iconic images!

[@chrishansen724]

I'm a software testing professional, thankfully retired and also thankfully not responsible for testing the DLR. I agree that testing impossible scenarios to see what happens is an important part of the testing biz. Thanks to your correspondent for the detailed explanation.

[@jimbegin6554]

Thanks for keeping me the “loop”!

[@thomashenden71]

Regarding how weird this connection was, with "computers out of sync", it was very interesting to hear about, and yes, a "routine test" discovering such an unlikely scenario, before it some day, resulted in an accident, must be considered extremely successful.

[@GBR481]

That is where my old school is! I’ve heard lots about the crash from my father.

[@MissCalatia]

Thumbs up if you like pretending to drive on the DLR 🙂

[@pmberry]

The Tyne & Wear Metro offers the same thrills, if you're ever up that way.

[@felixleiter9123]

i love to ride upfront as you make the severe turn past the ceneplex going into canary wharf station. feel like a lad again!

[@Otacatapetl]

To be fair, we always did it on the top deck of the bus.

[@ОльгаГарштя-и4ь]

I saw a sticker with buttons and levers at driver’s panel in Paris Metro 😊

[@hairyairey]

I once had the keys after one of the staff dropped them "Just what I've always wanted, the keys to my own DLR train!" I exclaimed then gave them back.😂

[@gardenlizard1586]

Good journalism to do corrections. 👍 Well done

[@edrose5045]

The first real-world buffer overflow error!

[@Satters]

definately not the first, the 1977 crash on the Stourbridge Town branch predates the DLR

[@robfinch3277]

A beauty, only IT guys will savour that!

[@toranine09]

for anyone whose curious, this ATP system is actually being applied to a large portion of the TFL rail network. geoff marshall has some good videos explaining how the system works!

[@pdrg]

Great video and thanks to the commenter who explained so clearly. Absolutely more videos like this!

[@MartinRobertson1969]

Well done on the best explaination of an asynchronous computer system clock cycle error I have heard in a publicly available video, complete with a real world example. It was well worth the correction.

[@dcmurray6466]

Fascinatingly interesting! Loved it! Thanks Jim.

[@IamTheHolypumpkin]

Asynchronous Computing always a pain.

[@highpath4776]

@@Berry-fr5wj Dunno, it comes and goes.

[@musicforaarre]

I found the answer in your earlier video about Island Gardens and Millwall former stations. Thanks, Aarre Peltomaa

[@mikeclifton7778]

Makes perfect sense, thanks for the updated version.

[@Phil6219]

Great timing with this one mate, a pair of Merseyrail units ploughed through the buffers at Kirkby last night in their attempt at reaching Wigan ;) A very interesting video as always :)

[@1963TOMB]

Seems a strange computer interaction to me. In my experience an ATP computer controls the round train brake circuit directly: in the event of an issue anywhere on the train, e.g. a door is not properly closed, this circuit is opened (fail safe) and the brakes are applied or, if stationary, held on. On the Victoria Line the ATP consists of three identical computers running identical software: two of these computers must agree with each other at all times: it's called 'majority voting'. I spent several months in a factory testing the interface between the Victoria Line trains ATP system and the radio system that conveys the data messages between the lineside signal systems and the trains; then I went to site to commission said radio systems.

[@DuskHorizon]

Computers in the 80s were less complex, which generally meant you needed more of them. It was the interactions between your multiple computers that added the complexity. Besides, making a single computer control everything is not foolproof either, just look up Therac 25 for a proper horror story.

[@QPRTokyo]

Thank you and Jim. 😷🦠I found this very interesting. Thank you.

[@wceyuki]

I’m here 3 minutes after release. Fastest I’ve ever arrived for a Jago video. Probably because it’s about the DLR, perhaps?

[@MirzaAhmed89]

Three seconds would have been more appropriate.

[@twotone3070]

Will that been you are going to be buffering?

[@birdbrain4445]

You're spot on. This is a pretty great example of why safety testing is very necessary, how it should be done, and the exact things that should be tested for. A lot of accidents in the world of public transport stem from those cases that are seemingly improbable, that no one even thought could happen or no one bothered to consider. And sure - on any given day the probability of such an occurrence is perhaps very low. But day after day, with dozens, hundreds or thousands of vehicles operating many many trips a day building up into millions of trips in its lifetime... those tiny probabilities add up, and the end result is that the seemingly improbable can and does happen. And in the absence of safeguards against it, or procedures for dealing with it, that can lead to devastating consequences. An accident like this is kind of the exact thing safety testing is supposed to lead to in a sense, it's supposed to root out issues like this; you can argue it was a good thing it happened (it helps that no one was hurt in the process.) The changes that were made in the aftermath, based on what was learnt here, have made the system a whole lot safer than it otherwise would have been. As soon as you said the three computers operated asynchronously I had a feeling it was going to be some case of them being misaligned, and yeah that was the case basically. Great video!

[@dickiedollop]

Great insight into the DLR I agree with the assessment from the operator over the failure 👍🏻

[@octoberspirit]

This is so interesting! I'm glad you got that email, and that you made this video rather than becoming a lighthouse-keeper. :3

[@spalftac]

I can’t help but think that placing a giant sponge at the end of the line would have been more effective.

[@SecretSquirrelFun]

YES, exactly!

[@mkendallpk4321]

How about a buffer with a big spring? I'm sure Sponge Bob Square Pants doesn't want to stop trains.

[@highpath4776]

@@mkendallpk4321 Most buffers have springs, often in a bath of viscos oil.

[@spalftac]

@@mkendallpk4321 That might work but avoid buying them from ACME as their products have some serious health and safety issues.

[@michaelcherson4495]

@@spalftac But Wylie E Coyote highly recommends them! I guess I should listen to that little bird that goes 'Beep, beep!" instead.

[@paullatimer9249]

Great video! Thank you for the thoroughness!

[@owentaylorwork]

Great video. And enjoyed the story behind that event

[@General_Confusion]

But was it wise to test a new train going at a faster than normal speed with a new computer system, on a line that actually did end 30 feet up in the air? Couldn't they have tested how well a train stopped on a piece of track that continued, just in case the train in fact didn't.

[@erejnion]

Well, the topology of the track is already inputted in the computer, tho. So the testing at the actual end of the track also tests whether the topology of the track is inputted correctly. Changing the end point removes this part of the equation. They indeed COULD have figured this exact bug on some other station tho, I must say.

[@cooperised]

Yes... though at some stage a "real" test would still have been a good idea. One where there is no artificial test harness, no possibility whatsoever that the test conditions didn't reflect reality for some unforeseen reason. Admittedly there might have been better choices of termini, for example one not built on a viaduct...

[@tech34756]

At some point testing like this would still be wise, for example, if the data at this station is incorrect or some other unique issue comes up as a result of it being the end of the line.

[@franl155]

But surely, even if a test for Site A is undertaken at Site B, and passes with flying colours every time, it still won't prove that it'll pass at Site A until and unless it's tested at Site A. Apparently trifling variations in elevation, construction, angles and so on could make all the difference.

[@fat_biker]

@@erejnion I think that after this testing failure they were able to re-use the whole crew & even, apparently, most of the train. I'm not sure that would have been true if they'd done the test somewhere where the train would have hit a station building if it overran the buffers... although maybe they _were_ testing in every location that an emergency automated stop might be required & it's just luck that the failure occurred where there was nothing solid to hit?

[@misterthegeoff9767]

As someone who knows more about software testing for weird proprietary systems than I do about trains this video was a very interesting and informative video. Video.

[@Rextum]

Good to know that these things are properly tested! This type of accident actually makes me feel safer than the ones where lots of people get hurt👍🏻

[@no_one_of_that_name_here]

I missed this one at the time for some reason.. long live the algorithm I guess for serving it up today. But long live this channel most of all.

[@steve3291]

I worked for GEC Traction at that time. My colleague was the engineer on that DLR train. He was legging it to the rear with an oscilloscope in hand when the accident occurred.

[@TEBEnthusiast]

It’s a good day when jago uploaded

[@simonmikkelsen]

Software engineer here: The test was successful and it was good the error was found without the public in the train.

[@tomgirldouble3249]

I love the run into Woolwich Arsenal from the front, it's like a minor rollercoaster...very minor 😆

[@timsully8958]

Ah yes, the charge of the Bank Brigade! 🤣😂😅 Spot on. It was the same when we got on at the old Island Gardens. My girlie and I used to happily wait for the second train by going via the shop so by the time we arrived we knew we would have “pole position” for the following train as Zoe loved the trip especially the rollercoaster down to Bank! 🤪 As a driver of a big train, I totally concur with the importance of safety measures. Sadly we often have tragic accidents that cause changes: let’s be glad that in this case there were no fatalities or injuries involved 👍🍻

[@RebMordechaiReviews]

Very clearly explained. Well done. There is a similar communications method employed when severs within a Load Balancer Cluster Web site talk to each other using a round robin heart beat method. However, a few seconds of discrepancies between a web page from server to server, won't make that much difference. When you are trying to stop a train or even worse, change course of an aircraft however, then a half a second can mean the difference between life and death. Therefore, this communications method is NOT recommended and is not employed for real-time systems today.

[@tr1ck5h07]

DLR content is always appreciated!

[@gritintheoyster]

Just came across this. I love the use of Rockwell font, the old typeface of the original DLR incarnation, in the captions on the locations. I worked for the London Docklands Development Corporation at the time and remember the accident well.

[@jimhunter5933]

Hidden flaws seldom remain that way! With 30 years of offshore energy control systems experience, my philosophy is to test, test and test again before you let it loose into the wild! Great video, as always.

[@tlillis4]

As someone who spent many years working in computers that is a great explanation - thank you for sharing. As you point out that is the reason to perform these sorts of tests before paying customers start riding. I can’t help but think DLR compares favorably to New York’s MTA. The motorman (driver) of the JFK AirTran was killed when the weights on the train used to simulate passengers broke loose and crushed him. On a lighter note, “driving the train” is a well-known past time on the NYC Subway and people of all walks regularly elbow their way to the front of the first car. In 1972 the NYCTA introduced the R44 which had all sorts of features (bucket seats!! door chimes!!). They became quickly unpopular because they had a full-length cab which meant you couldn’t “drive the train” nor walk between cars. Both major “no nos” to New Yorkers! Even today you can look out the front car of nearly all of MTAs rolling stock - even the suburban train lines.

[@ValueNetwork]

I’m now officially hunting for mistakes in this video, mainly because I want you to make a video about lighthouses if someone finds a mistake

[@andreww2098]

as i mentioned in a comment, working Lighthouses are all automated there are no lighthouse keepers, Trinity house updated the last one in 1998!

[@pavlekodak2147]

Andrew - yes, and that's why we want video on the life of lighthouse keepers before automation and after with all saucy details

[@MirzaAhmed89]

"I hope you enjoyed this illuminating video..."

[@highpath4776]

@@MirzaAhmed89 Can you check if the lighthouse is working. No... Yes... No... Yes... No its off again, wait its back, no I was wrong, yes its OK, damn gone again.

[@danielvanced5526]

They still have a one second cycle on the inductive loop communication. You can accidently switch to "Emergency Shunt", which is easy to do, but should never be done without authorization. If you switch back quick enough (before the next cycle) it doesn't report it back to control and it just looks like the train dropped out of ATO.

[@hughdanaher2758]

A similar accident happened on the BART system when a train over ran the station in Fremont, California.

[@MossdaleNGaugeRailway]

The original signalling system on the DLR was loaded from 8 inch floppy drives, that’s the only time I have seen that size in use.

[@stefanj3012]

I guess I’m giving away my age if I say I have used 8 inch floppy disks 😎

[@tech34756]

I think the US military still uses them for their nuclear missiles.

[@allangibson2408]

I used 8” floppies in the late 1980’s to load operating system updates to an 8” 5Mb hard disk system used for industrial controls.

[@davidsummer8631]

I think Matthew Broderick used 8 inch floppy disks in War Games

[@AtheistOrphan]

@@davidsummer8631 - You beat me to it! ‘Shall we play a game?’

[@legionnairegonk4425]

Better to find out in testing - that is what it is there for 😉 Congrats on 100k too 👍

[@AkisHajittofi]

My first time ever riding the DLR was when I started at University of Greenwich! The first time was an amazing experience, I remember saying as soon as it starting moving, "this is shaky" haha, but I was amazed with everything about it such as the scenery and its uniqueness to other lines... I just love the DLR! I live in North London and I commuted to uni, I'd take the Overground to Liverpool St, then that horribly overcrowded central line to bank (I sometimes walked it between the stations but most of the time I didn't), then finally the DLR to Cutty Sark.

[@tjejojyj]

Excellent video. It just proves why extensive testing is necessary. I would like to know how many tests they were planning to do? Or they normally do? Please do a video on the testing of the Victoria Line.

[@lwilton]

Yep, safety testing is a good thing. The modern world seems to have completely forgotten that not all tests result in 100% success. Some result in a failure that you can learn something from, and make changes so it doesn't happen again. In many ways there are more valuable and contribute more to gained knowledge than the successes. When man was learning how to get into space 70 years ago there were a whole lot of tests that blew up or went corkscrewing sideways, and each one was a success in that they learned from it and the same thing didn't happen again. Now we expect all "tests" to merely be PR shows.

[@57thorns]

People are relearning that during SpaceX Starship tests now. And those tests were only "successfull" in the sense that they did not show any flaws in the actual tests.

[@beeble2003]

It shouldn't take any testing at all to realise that three computers running asynchronously on one-second cycles can take up to three seconds to come to a decision, and that such a system therefore cannot guarantee a response within 2.7s. Having said that, I just can't believe the explanation in this video. If the train started braking 0.3s too late, it would have stopped 0.3s too late, and that shouldn't have resulted in anything worse than stopping very slightly closer to the buffers than normal. You don't go off the end of a viaduct by hitting the brakes a third of a second late.

[@57thorns]

@@beeble2003 You are right in that those 0,.3 seconds are not the whole picture, can't be. Unless someone thinks safety margins are for losers.

[@davidioanhedges]

@@beeble2003 ....Breaking from high speed, which it was, 0.3 s can make a difference of a few meters which was all it travelled

[@beeble2003]

@@davidioanhedges Oh. Duh. For some reason it didn't occur to me that braking 0.3s late means spending an extra 0.3s at whatever speed you were doing _before_ braking started. Duuuuuh. But, still, there must be multiple factors in play, here: unless they were Hail-Mary testing the emergency brakes from the last possible point they could be applied, the system should have had plenty of time to see it needed to brake harder.

[@herpderp3131]

Great video, thanks Jago