The Island Gardens Accident: What Really Happened
Вставка
- Опубліковано 13 бер 2021
- 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...
Patreon: / jagohazzard
Ko-Fi: ko-fi.com/jagohazzard - Розваги
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.
A better fool!!! Don't you mean a fully qualified fool? There's nothing 'better' about being a fool.
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
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.
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.
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. 😀
This is why you test. This is where you learn the most.
♬ For the good of all of us... ♬
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.
Absolutely. You learn more from mistakes. Granted, it's an expensive mistake, but it saved a lot.
Testing at the end of the line with a vertical drop was a good idea then? 🤣
@@creamwobbly No. But testing at another station with some 'just in case track' would of been less risky!
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.
Or, as it's known, being a passenger
"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
So much of life is "to combine nonchalance and apparent disinterest with extreme aggression and ruthlessness," isn't it?
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.
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.
This is the best “apology” video I’ve seen on UA-cam! This is excellent technical geekiness we all need and want!
Many thanks!
I see it as more of a "clarification" video.
@@mirzaahmed6589 - that might have been the word I was searching for at 8am this morning!
CGP Grey’s “I was wrong” was spectacular too
I bet the DLR's mother called it by its full name that night when it got home...
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.
DOCKLANDS LIGHT RAILWAY WHAT TIME DO YOU CALL THIS?
JAMES PETER DOCKLANDS LIGHT RAILWAY SMITH what on EARTH do you think you're doing?!
@@robmarkworth5377 ALEXANDER DOCKLANDS ILYICH LIGHT KONSTANTINE RAILWAY! You have overshot the mark and brought shame to mamma!
@@davidbull7210 Some said he was not going to fast. Others said he was Rushin
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.
Graeme Garden made that mistake...
That's been used a few times on tv; was it not used on Dinner Ladies and, I think Only Fools and Horses?
Yeah, uniforms are totally different.
With lighthouses and housework, there's a four candles joke in here somewhere.
And there is a big difference in a "chicken ranch" vs a "chicken farm"... The former will most likely get you into legal trouble... :)
Very appropriately described as a “loophole” given the 3 computers and their individual one second loops!!
It did sound as if Jago missed his unintended pun, though... :-)
Yeah - I caught that 'loophole' bit, as well; textbook definition, to be sure.
I think the computers were a little loopy.
This is what interrupts are for. "Stop what you are doing and listen right now, this is important!"
@@ShaunieDale Maybe the tech was "interrupted" just before entering the relevant script into the software. Oh dear.
Just another buffer overrun.
Best comment so far! :D
Brilliant!!
I'm glad I wasn't there. I'm an old buffer.
Involving both a physical buffer and a computer buffer.
Very witty! I’d be proud of that comment.
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.
Thanks!
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!
Async programming is always "fun"
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.
As soon as I heard '1 second processing loop' I knew what went wrong...
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...
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!
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.
Yeah, but it was in the '80s, less elf and safety, and also not the first time something like this had happened.
It is entirely normal in railway safety to fully test safety critical edge cases.
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.
@@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.
Thumbs up if you like pretending to drive on the DLR 🙂
The Tyne & Wear Metro offers the same thrills, if you're ever up that way.
i love to ride upfront as you make the severe turn past the ceneplex going into canary wharf station. feel like a lad again!
To be fair, we always did it on the top deck of the bus.
I saw a sticker with buttons and levers at driver’s panel in Paris Metro 😊
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.😂
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
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?"
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.
@@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.
Good explanation. I didn’t get confused once 😀.
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
Oh it was you
The train was under *test.* Many *tests* have no success or failure, only a result to be analysed.
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.
@@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.
Was undertaking the test at the end of the line with a 10 metre drop, a successful outcome of a failure to plan?
@@sumpyman
That test lacked a safety margin.
@@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!
If this explains in a nutshell why Crossrail is taking so long, then it will probably have been worth the wait...
Software testing is very very time consuming.
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
@@user-de4cq6uk6l Still, it will be worth it if "signalling" is ever to be installed on another railway. Pioneering is hard.
@@bfapple unless you are a games company then you rely on end user testing (mutter, mutter, Bethesda!)
@@andreww2098 I'm still waiting for a cheque from R* for beta testing rdr2 for them.
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
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!
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.
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!
@@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 UA-cam came along a little to late to record their experiences.
Thanks for sharing. Nice.
@@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.
Being the son of a railwayman, my father would often ask the driver if I could ride up front when I was a nipper.
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!
The first real-world buffer overflow error!
definately not the first, the 1977 crash on the Stourbridge Town branch predates the DLR
A beauty, only IT guys will savour that!
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.
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.
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!
Asynchronous Computing always a pain.
@@Berry-fr5wj Dunno, it comes and goes.
I can’t help but think that placing a giant sponge at the end of the line would have been more effective.
YES, exactly!
How about a buffer with a big spring? I'm sure Sponge Bob Square Pants doesn't want to stop trains.
@@mkendallpk4321 Most buffers have springs, often in a bath of viscos oil.
@@mkendallpk4321 That might work but avoid buying them from ACME as their products have some serious health and safety issues.
@@spalftac But Wylie E Coyote highly recommends them! I guess I should listen to that little bird that goes 'Beep, beep!" instead.
Can you imagine the sort of testing NASA must get into? A great explanation, very clearly expressed.
I can, the same for anything flight related inside the athmospehere.
That train nearly became a flight....
Hmm, like rockets and programs that a calibrated in the wrong dimensions (m instead of mm for example, or squashed O rings).
@@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...
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.
I have always quite fancied being a lighthouse keeper. Stormier the better. Just as long as I can still watch my football and have plenty of pizza making supplies.
When I was a kid, my primary school had an exercise where we each picked a lighthouse, and wrote a letter to the keeper. I got a nice reply! I decided then I wanted to be a lighthouse keeper when I grew up, but then Trinity House went and automated the lighthouses, and that job pretty much died out.
Don't watch The Lighthouse. It'll put you off big time. LOL
Software engineer here: The test was successful and it was good the error was found without the public in the train.
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.
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.
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...
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.
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.
@@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?
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. 😃
Thanks for including the technical information. As a programmer it's very clear.
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.
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.
I'll be sharing this with my A-Level Comp Sci classes :) this is brilliant Jago!
Thanks!
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!
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.
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.
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!
Thanks for the video Jago.
You learn more from mistakes and things going wrong than when things go right. Thanks for producing this excellent video!
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.
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!
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.
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.
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.
@@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.
@@beeble2003 ....Breaking from high speed, which it was, 0.3 s can make a difference of a few meters which was all it travelled
@@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.
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.
I guess I’m giving away my age if I say I have used 8 inch floppy disks 😎
I think the US military still uses them for their nuclear missiles.
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.
I think Matthew Broderick used 8 inch floppy disks in War Games
@@davidsummer8631 - You beat me to it! ‘Shall we play a game?’
Been in the rail industry 25 years and it's interesting to see the technical side of the test procedure
You are the man. I wish a lot more UA-camrs were more like you
To make it even more interesting you added humour and wit to this video 👏🏾👏🏾👏🏾👍🏾👍🏾
Thanks Jago for making an exception and to Jim for his very understandable explanation.
If Boeing made trains there would have been passengers on it.
Or they would all be over budget and then cancelled
Boeing used to make trains.
The Boeing LRV also called US Standard Light Rail Vehicle.
They where so heavy, noisy, frequently derailed, broke down so often there the mean time between failures was so short that often only half of the rolling stock was operational.
They where so bad that Boeing couldn't produce enough replacement parts for them. So in Boston they started to cannibalize some of the cars shortly after they went into operation just to get enough replacement parts to keep the remaining cars operational.
But here is a funny quote from the Wikipedia Article:
"Before they were delivered, Boeing claimed the US SLRV would be reliable and virtually maintenance-free."
Only two Transit systems ever bought those car.
The Boston MBTA and San Francisco SFMTA (Muni)
Here it the Wikipedia link;
en.wikipedia.org/wiki/US_Standard_Light_Rail_Vehicle?wprov=sfla1
They designed the cars for the PRT system at West Virginia University back in the early 1970s.
@@DarkAudit Ok so Boeing did build trains, egg and my face were in alignment.
Growing up whenever I heard a plane had crashed I knew it was a Boeing.
Seeing a new Jago video in the mornings makes waking up not so bad..
Also hey 100K! 🎆
Geoff Marshall would’ve filled you in on a lot of things, I met him once filming at Victoria in London and his knowledge of facts about these types of lines is phenomenal.
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
as i mentioned in a comment, working Lighthouses are all automated there are no lighthouse keepers, Trinity house updated the last one in 1998!
Andrew - yes, and that's why we want video on the life of lighthouse keepers before automation and after with all saucy details
"I hope you enjoyed this illuminating video..."
@@mirzaahmed6589 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.
One hopes that Tesla et al are still testing their autonomous car systems.
Of course, they're testing them on their unsuspecting drivers in the real world ! The NTSB is pretty miffed about it...
I’m here 3 minutes after release. Fastest I’ve ever arrived for a Jago video. Probably because it’s about the DLR, perhaps?
Three seconds would have been more appropriate.
Will that been you are going to be buffering?
Good journalism to do corrections. 👍 Well done
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.
Thanks for the info. Always a pleasure to watch.🙂
I would love to see you do videos about being a lighthouse keeper, I imagine they would be wonderful.
Great video! Thank you for the thoroughness!
Really neat video, thanks for putting it up. Interesting case study for system design.
The content gets better and better. The presentation hits the mark every time. Where will it all end?
Congratulations on 100k subs! Keep up the good work :)
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!
Makes perfect sense, thanks for the updated version.
Fascinatingly interesting! Loved it! Thanks Jim.
Congratulations on 100,000 Subscribers! 🎉 😃
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👍🏻
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.
Thank you and Jim. 😷🦠I found this very interesting. Thank you.
Great video. And enjoyed the story behind that event
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!
Congratulations on 100,000 subscribers :) .
Very clear explanation of the computing issues there!
Great video, thanks Jago
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.
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.
Great video and thanks to the commenter who explained so clearly. Absolutely more videos like this!
I used to catch the DLR to/from Elverson Rd every day for 10 years. Thanks for showing footage of that route.
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!).
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.
Thanks for keeping me the “loop”!
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 :)
I found the answer in your earlier video about Island Gardens and Millwall former stations. Thanks, Aarre Peltomaa
Great insight into the DLR I agree with the assessment from the operator over the failure 👍🏻
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.
Of course the Therac was never properly designed, documented or tested before release into the real world. The DLR was.
That's what software interrupts are for 👍. Good to know they saw it and fixed it.
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.
Very interesting video. Thank you!
This is so interesting! I'm glad you got that email, and that you made this video rather than becoming a lighthouse-keeper. :3
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.
It’s a good day when jago uploaded
I enjoyed this a lot, thank you very much.
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? 😂😂😂
Many , Many , Many times, I guess.
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.
Superb video as always! I do enjoy a good DLR video
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 👍🍻
What better explanation can there be why NOT to sit at the front of a DLR train 😲
Well, if at the front you get to see it going wrong rather than it coming as a surprise. Although I'm not sure which to choose.
@@twotone3070 😂
That is where my old school is! I’ve heard lots about the crash from my father.
Loved it. Good stuff. Thank you.
I love the run into Woolwich Arsenal from the front, it's like a minor rollercoaster...very minor 😆
Back many years ago, around 1971 a similar thing happened with the new San Francisco BART system, resulting in a new train driving past it's stop, through a fence and crashing into the parking lot. Software is funny stuff..
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.
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 ?
@@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.