[HN Gopher] How we slowed the subway down
___________________________________________________________________
How we slowed the subway down
Author : gok
Score : 263 points
Date : 2022-12-23 23:41 UTC (23 hours ago)
(HTM) web link (homesignalblog.wordpress.com)
(TXT) w3m dump (homesignalblog.wordpress.com)
| dzdt wrote:
| After an operator-error derailment on the commuter rail line I
| frequently ride, the response of the NTSB was to require the
| railroad de-prioritize on-time performance and increase schedule
| times. As a frequent rider on the route I would much rather have
| my 15 minutes per day back and risk a once-per-century fatal
| accident. But the risk-averse bureaucracy we've built doesn't
| make such calculations with a balance like that: they prioritize
| safety above all else never mind the detriments.
| poslathian wrote:
| I often wonder how we might estimate how much of the surplus
| created by economic growth and technology has been hoovered up
| by "alarp" in its many forms. I'm scared of the answer, and of
| the people who wouldn't see a problem with it.
| concordDance wrote:
| For those wondering:https://en.m.wikipedia.org/wiki/ALARP
|
| As Low As Reasonably Practical
| thrashh wrote:
| It's not a bureaucracy thing IMO
|
| People are severely spooked when they hear people are injured
|
| If you have customers and you want to continue having
| customers, you really have to manage your PR. Injuries look
| really bad
| joe_the_user wrote:
| A bureaucracy can't ignore the possibility of a deadly crash.
| But they chose the slow-down instead of spending the money
| needed for safety. Which is despicable imo. But there is the
| quandary that they know a modernization project could be a
| disaster just all American public transit projects tend to be
| disasters.
| danuker wrote:
| Reminds me of Atlas Shrugged, when they had to resort to
| manual track signal switching.
|
| "Physical men, serving as lamposts. You've advocated it long
| enough--you've got what you wanted'" (pp. 875-76).
| hristov wrote:
| "Sure you save some lives but how many will be late!" I do not
| like this math. For example the accident may not be once per
| century. And it is good for the bureaucracy to be risk adverse
| if it comes to my life.
|
| The answer is that they should improve the technology so that
| the system is safe and faster.
| Dylan16807 wrote:
| > And it is good for the bureaucracy to be risk adverse if it
| comes to my life.
|
| Only moderately risk adverse.
|
| Unless you'd approve of all roads having a 15-20mph speed
| limit? Because that's the natural conclusion of prioritizing
| accidents much higher than speed. And I'm not being
| hyperbolic or using a slippery slope argument. I'm saying
| that you _have_ to admit a tradeoff to get any kind of
| sensible result.
| quotemstr wrote:
| > I do not like this math
|
| Many policy difficulties arise from unwillingness to trade-
| offs between "sacred" and non-"sacred" values. It's easy to
| say that just one life is worth an arbitrary amount of non-
| fatal inconvenience to an arbitrary number of people. It's
| the cheap, easy platitude anyone can summon in a meeting. It
| feels good to say. Simple. Strong. Righteous.
|
| But the world doesn't work this way. Mere life does not, in
| fact, have infinite, overriding value. Infrastructure
| engineering is not a morality play. It's a complex set of
| trade-offs, some involving safety. In a big system like
| public transit, as crass as it might be to say explicitly,
| the optimal number of deaths is seldom zero. Safety and
| utility are not, as the moralists might insist,
| incommensurable. They in fact exist on the same plane, and to
| build things that are effective and efficient, we need to
| trade them off against each other. Failure to do so leads to
| cowardly paralysis.
|
| In other words: yes, we absolutely should accept some
| statistical nonzero risk of injury to save time or money in
| the overwhelmingly common case, because these things
| _matter_.
| maria2 wrote:
| Many lifetimes of time are being wasted every day to save <
| 10 lives every century.
| googlryas wrote:
| Lifetimes aren't composed of tiny time slices of many
| people.
| nitwit005 wrote:
| Ethics discussions often involve this sort of idea,
| although it's usually in terms of life-years.
| jraph wrote:
| Life can't be reduced to (productive) time like this. At
| least I find this take very sad.
| quotemstr wrote:
| > Life can't be reduced to (productive) time like this
|
| Yes it can, and it's essential that we do it, because the
| alternative is a ruinous level of risk aversion.
| ErikVandeWater wrote:
| The time they spend on the metro isn't necessarily
| productive time. Many people would be enjoying leisure
| with that time.
| maria2 wrote:
| Why do you find it sad? Everything has a cost. There are
| plenty of things that harm people every single day that
| we tolerate readily. For example, 91 lumberjacks died
| last year. There are way fewer employed lumberjacks than
| there are subway riders.
| closeparen wrote:
| You're right, it's even worse than that. When public
| transit is constantly decelerating, crawling, and
| hesitating it (correctly) communicates to the riders
| society's judgment that they and their destinations don't
| matter. That if your trip mattered you would have your
| own car. It sets a waiting room atmosphere. Public
| transit is a purgatory for those with nowhere else to be
| to while away the hours. And pretty soon that's who your
| ridership is and what they're doing there.
| nullc wrote:
| You don't necessarily need to make that comparison: If
| you make the trains too slow many people will drive
| instead which is radically more likely to kill them than
| the train.
|
| So you can still find that there is a speed risk tradeoff
| the minimizes death which is not the same as minimizing
| the train risk.
|
| Worse for NY's problems is that in that decision people
| are probably using something like the 95-percentile trip
| time as the criteria: It doesn't help them if the train
| is fast on average since they need to schedule for the
| worst-likely case. The fact that the crews are playing
| roulette with an kafkaesque speed limiter system and
| risking disciplinary action should they anger it
| essentially guarantees that the times will be both slow
| and highly inconsistent.
| jraph wrote:
| Indeed fully receptive to this argument.
| rocqua wrote:
| What death risk are you talking about? Seems like an
| interesting anecdote.
| JumpCrisscross wrote:
| > _the accident may not be once per century. And it is good
| for the bureaucracy to be risk adverse if it comes to my
| life_
|
| People stop taking the subway when it takes too long. That
| not only increases traffic, it also saps the system of
| funding.
| gruturo wrote:
| If OP's subway carried 80k people per day (and I guess this
| could be conservative), and they are all delayed 15 minutes,
| the overall wasted time equals 1 lifetime per month.
|
| I'm all for improving the technology, but in the meantime the
| math should absolutely be done, at least to ensure the
| temporary fix isn't worse than the problem.
| Retric wrote:
| There are feedback mechanisms here which shift where people
| live and work in response to changes in transportation
| times. Which means you can't simply extrapolate like that
| over time.
| vosper wrote:
| Is it necessarily wasted, though? If the subway is tedious
| and unpleasant, then sure. But if I get a seat and I get 15
| more minutes reading or staring out the window, then I'm
| probably not calling that a complete waste.
| rayiner wrote:
| Getting a seat on the NYC subway? Lol.
| nine_k wrote:
| Quite doable these days; I'd say 90% of my recent rides
| (Q, B, A, C lines).
|
| Was a total piece of cake in 2020, of course %)
| ErikVandeWater wrote:
| If you told New Yorkers they had the option to live 15
| minutes longer, but that is added time on the NYC subway,
| I think most would turn it down.
| concordDance wrote:
| You need to adjust for the QALY level of riding a train
| compared to the rest of people's lives. Train riding isn't
| much fun, but it's much better than being dead.
|
| Your point probably still holds though.
| bee_rider wrote:
| Jokes aside time spend on the subway isn't actually
| equivalent to time spend dead, we shouldn't trade them one-
| for-one.
|
| Also the "one extra death per century" measure seems to be
| derived via the method of rectal extrication, we don't know
| how many deaths a schedule change might cause or prevent at
| all, and I bet the people working on the subway have, if
| anything, some idea with massive error bars.
|
| I dunno the math seems basically impossible to do, I mean
| it would have to include things like "how to people,
| possibly irrationally, respond to deaths on the subway."
| barry-cotter wrote:
| > "Sure you save some lives but how many will be late!" I do
| not like this math. For example the accident may not be once
| per century. And it is good for the bureaucracy to be risk
| adverse if it comes to my life.
|
| I hope you're campaigning for a nationwide speed limit for
| automobiles of 20mph. It is good for the bureaucracy to be
| risk averse with loves after all.
| kccqzy wrote:
| When the train is often late, it simply pushes people to
| drive more, and depending on the specifics driving on the
| highway could very well be less safe. Ergo, it results in a
| net loss of lives. This is pointed out near the end of the
| article.
| nostromo wrote:
| > "Sure you save some lives but how many will be late!"
|
| You make this trade off every day without admitting it in
| such stark terms.
|
| Every time you drive, bike, or fly to a destination you're
| choosing speed at an increased risk of injury or death.
| concordDance wrote:
| Note that flying is safer than walking.
| gok wrote:
| Practically what happens is many people switch to driving and
| waste more lives
| rocqua wrote:
| How much delay is acceptable for a 0.001% point yearly
| mortality reduction on a busy rail line? Certainly not an
| hour. So there is some tradeof.
|
| Notably the lives OP was talking about included his own. I
| think that matters quite a bit. Risking your own life for
| better speed is a different ballgame than deciding the risk
| other people run is fine.
| fukutyphoo wrote:
| Fukushima nuclear power plant in Japan had a system designed
| for a 1 in 100 year accident. It happened after 8 years.
| https://www3.nhk.or.jp/nhkworld/en/ondemand/video/3016087/
| PS, this is a great video about the typhoon that caused the
| disaster.
|
| Disasters are Black Swan Events
| https://en.wikipedia.org/wiki/Black_swan_theory in Talebsbook
| he explains (ok it's a theory) that rare events happen
| commonly.
|
| See also Terry Pratchet "one in a million chances happen nine
| times out of ten"
| nkrisc wrote:
| Kinda sucks for the people who get killed so you can arrive
| sooner though, right?
| rtpg wrote:
| What if we actually just operated trains safely, made
| improvements to the system, and then sped things up _because we
| improved the safety to make it possible?_
|
| "We risk crashes or make everything slow" is a false choice
| when we're talking about years-long perspectives. Especially
| given that there are lots of contributors to throughput and
| slowness.
| themitigating wrote:
| But if you were in that accident or a parent/friend in it you'd
| have the opposite opinion and demand "the politicans make
| things safer "
|
| You're just a selfish npc
| valyagolev wrote:
| this is the kind of nitty-gritty stuff I wish railroad management
| games would show, a lot of them are very arcade-like in
| comparison
| breck wrote:
| tldr;?
| rocqua wrote:
| Signals designed for slower trains were unsafe with faster
| trains and bad maintenance unless the separation between trains
| was massively increased and speed limits were aggressively
| enforced.
|
| Bureaucracy was slow to recognize this causing accidents. Then
| in an overreaction to accidents they added slowdowns and
| increased separation, without doing a whole overhaul of the
| system. Then maintenance issues on speedometers and speed
| signals forced trains well below speed limits to prevent
| accidental triggering of speed signals. Also trigger spreed
| signals that were known to be defective was blamed harshly on
| operators.
| danbmil99 wrote:
| This reminds me of the trouble they've had upgrading Air Traffic
| Control systems.
|
| I grew up in Manhattan and rode the subway constantly. I remember
| sometimes taking the front car, looking out the window and
| wondering what the odds were of a collision. Then a friend
| explained how the red light control system made it physically
| impossible for one train to crash into another.
|
| Ha! Glad I didn't know the truth back then, I might have
| developed a phobia about using the subway.
| lifeisstillgood wrote:
| My takeaway: imagine we decided the _enforce_ no crashes on
| roads. The second a driver comes too close behind another car or
| breaches speed limits, the car enforces their brakes on.
|
| Yeah I can see how the knock on tailbacks and flow will make
| roads insane.
| rocqua wrote:
| Self-driving convoying essentially boils down to doing this.
| The problem in your approach is fully locking the brakes rather
| than slightly decelerating the car.
|
| I'd also guess that after 2 years of your system most people
| would manage to keep their distance. Would probably work great
| except for merging.
| lifeisstillgood wrote:
| I am however convinced by the "less cars, not self driving
| cars" argument.
|
| Urban redesign, reclaiming back some of the on average 1/3 of
| city surface area dedicated to cars / roads, more reliable
| public surface transport (I mean are we seriously asking "can
| we increase the likelihood of a subway crash in order to
| increase capacity" instead of asking "why don't we have
| hundreds or thousands more buses on the roads"?
|
| There is a whole polemic Inshoukd be writing about how
| societies use stickingmplaster solutions over actual
| solutions - from Iran 1956 to 6th gen aircraft, meat eating,
| brexit,
|
| it's a long polemic
| rocqua wrote:
| In America, you are presumably correct, though it is
| somewhat of a false dichotomy. In less car based countries
| like my home country the Netherlands, there isn't as much
| room for 'less cars' (though still plenty, just nowhere
| near as bad as America). Hence self-driving cars here are
| more important.
|
| Besides the solution in America is likely to be both less
| cars and self driving cars. So it's not like self driving
| cars aren't worth developing. They are, however, not an
| argument that "we don't need to get alternatives to cars".
| lifeisstillgood wrote:
| The problem (as I see it) was s not R&D, it's human
| nature. If there is a possible self driving car we can
| put things off, imagine a different mix etc.
|
| Almost all of the climate chnage debate is really
| (excluding the fringes) not "is climate chnage real" but
| "exactly how much do I have to do to fix it".
|
| An analogy is I don't dispute that I am overweight, and
| that will impact my lifespan, but t there is a debate on
| whether that means a calorie controlled plant based diet
| from tonight along with four hours in the gym each day,
| or I "make an effort to cut down".
|
| Imagine AOC and Greta Thunberg as the personal trainers,
| and Bjorn Lornborg as the CEO of low calorie beer and no-
| salt chips LLC.
|
| I think I have wondered off the point - but essentially
| we have within us the solution to all our ills. Politics
| is just the voices in our heads as we try to talk
| ourselves into going to the gym and sticking to a budget.
| kylehotchkiss wrote:
| This plus the well-documented safety issues happening on public
| transit across the country will keep the personal vehicle market
| strong for decades to come. There's no future in US where public
| transit is so good that it takes a notable amount of cars off the
| road until we can culturally conquer hard problems like these
| (like close down the line for 3 months to improve) and actually
| police the systems (fun fact - almost every big city in india has
| to go through metal detector and bag though x-ray to ride the
| metro, I'd love this in US)
| mildchalupa wrote:
| One of the things that I find interesting in terms of long
| lasting standard or infrastructure development is that small
| variations in design choices early in a system result in
| radically different performance down the line. For instance the
| width or guage of a train track will greatly influence the
| carrying capacity and the size of objects transportable via rail.
| Same for the size of lane of road. Infrastructure, and standards
| tend to have an inertia like quality as changeover to a slightly
| improved system takes significant capital.
|
| In general it seems absolutely insane to me that we rely on an
| antique control strategy for the Subway while in other industries
| outside of rail such as aviation or automotive such a system
| would be easily automated.
| pantalaimon wrote:
| The subway is actually a systems that is easier to change than
| others (unless you talk about the physical dimensions of the
| train) since it's an isolated system and lines are usually
| separate too, so you don't have to change it all at one.
| bregma wrote:
| You're not describing the New York City subway. The L line
| was separated from pretty much everything else so it got
| upgraded to CBTC over a few years as budget, time
| constraints, and politics allowed. The rest of the network is
| thoroughly interwoven and runs 24x7. It also carries more
| people daily than all the other systems on the continent
| combined.
| Tokkemon wrote:
| Sure, but the New York Subway is the most interlined metro
| system in the world. You have to essentially change
| everything at once, or at least go trunk line by trunk line,
| or run two separate systems concurrently. None of which are
| easy options.
| tgsovlerkhgsel wrote:
| The obvious solution seems to be to technically enforce the speed
| limits _without_ relying on average-speed-through-section, which
| seems to have been done way too late.
|
| Likewise, the yellow signals could trigger enforcement of a
| braking curve to ensure the train will have a sufficiently low
| speed at the next red signal. (This is how one of the German
| systems works - PZB, not a modern one either, I think the
| braking-curve-enforcement was introduced in the 1950s.)
|
| _Especially_ if the "too much acceleration" problem only
| applies to new trains, that also conveniently addresses the
| upgrading issue - old trains accelerate slow enough to be safe
| under the old rules, new trains can have e.g. a speed limiter.
|
| It's also just one subway system, not an entire national railway
| network, which should make modernization a lot easier. But I
| guess given that apparently actually using regenerative braking
| was a new thing in 2018
| (https://www.progressiverailroading.com/sustainability/news/M...)
| despite the heat issues in the stations, I guess that's expecting
| too much.
| pantalaimon wrote:
| PZB was already introduced in 1934
|
| https://en.m.wikipedia.org/wiki/Punktformige_Zugbeeinflussun...
| usr1106 wrote:
| The previous commenter did not say PZB were introduced in the
| 1950s, but adaptation to braking curve. Not an expert in the
| area, but I very vaguely remember that 1 out of 3 braking
| curves is selected for each train. Not sure how big the risk
| is that trains would operate under the wrong braking curve
| and whether that has ever materialized in form of an
| accident.
|
| Edit: Selecting a braking curve seems important when the same
| engine can haul passenger trains and freight trains. That was
| rather common in Germany decades ago, probably less so today.
| Doesn't seem relevant for EMUs like on the NYC subway.
| hristov wrote:
| It is actually bonkers that in this day and age the NYC subway
| cannot install accurate speed gauges on their trains. You can get
| an accurate bike speedometer for $20 on amazon, but the NYC
| subway cannot provide an accurate speedometer for train carrying
| a couple of hundred people. It is true that trains require more
| rigorous standards, but it is not a difficult problem. For
| example you can put a sensor on the electrical motor that will
| accurately measure motor position. This will allow you to derive
| speed, as subway motors are directly geared to the wheels at a
| single unchanging gear ratio.
|
| Same thing for stationary speed sensors in the signaling system.
| It is maddening that they have to time a train over a distance of
| 50 feet and use an electro-mechanical timing mechanism. Which has
| to be regularly maintained and it tends to give wrong readings
| when not properly maintained, etc. Why not get an instantaneous
| speed reading with lasers? Those have worked for police officers
| for 40 years now. Or infrared. Or if you have to time a train
| over a distance time it with a purely electronic system over a
| distance of a couple of inches. There are definitely electronics
| fast enough to do that nowadays. And you can get a purely
| electronic system that requires zero or almost zero maintenance.
| woodruffw wrote:
| My understanding from TFA is that this isn't the problem at
| all: most (all?) of the modern trainsets do have speedometers
| that the conductor can read. The problem is not measuring the
| speed; it's that the city's signaling scheme no longer matches
| the handling conditions of the trains that run over it.
|
| In other words: the conductor might be operating the train at a
| perfectly reasonable speed according to their accurate
| instruments _and_ the track signals, but the track signals are
| no longer calibrated for their trainset or the upgrades done to
| it over the years. This has made conductors excessively
| cautious, precipitating the recent slowdown crisis on the
| subway.
| rocqua wrote:
| From the article:
|
| Unfortunately, thanks to a combination of poor design choices
| and poor upkeep, many of these speedometers have proven to be
| wildly unreliable. So, as train crews navigated the
| increasingly speed-controlled subway of the aughts, they not
| only had to build uncertainty around signal design, but
| equally about the accuracy of their on-train equipment.
|
| In other words the problem is both inaccurate signals and
| inaccurate speedometers. The combination requiring operators
| to be much more careful, and making them lose faith in their
| data. Exacerbating this is that signal trips caused by faulty
| timers were still blamed on operators. Making them also lose
| faith in management. Presumably, this wasn't good for the
| relationships between management and unions, hence probably
| contributing to strikes.
| notmtaemployee wrote:
| A couple of thoughts:
|
| The approach you describe to measure speed from the motor
| position is essentially what subway cars use. Ignoring wheel
| slip, which is not a rare phenomenon, this approach works very
| well. However, when you defer maintenance, things operated in
| harsh environments _will_ eventually break down.
|
| (Within the context of the issues mentioned by the linked 2018
| NY Post article) Speedometers were (bizarrely) judged as non-
| critical parts (i.e., the car can still be used in service with
| it broken) because, after all, the signaling system will catch
| any over-speed, thus the repair, and more importantly the
| maintenance, of speedometers was not prioritized. Thankfully
| most of Cuomo's goons and bean counters have been pushed out.
|
| As for the wayside speed enforcement, the author only briefly
| touched on the solutions to the problem described in the
| article, but it's known as Communications Based Train Control
| (CBTC)[1]. It's a moving block system (compared to current
| fixed block signals) that used train speed, track geometry, and
| the location of other trains to determine maximum safe
| operating speed.
|
| I would argue that it's not "maddening" to control subway speed
| with electro-mechanical timing mechanisms, control lengths,
| etc. This was cutting edge in the 1920s & 1930s, and indeed
| some of the oldest signaling in the system is from that era
| (though thankfully, the amount is decreasing).
|
| It is however maddening to decide in 1995, given other existing
| speed control solutions at the time (coded track circuits,
| CBTC, axle counters) to expand the use of these timers. But as
| the saying goes if you have a hammer, everything is a nail.
|
| Even more maddening is how slow the subway's transition to CBTC
| has been. NYCT was an early leader, with the Canarsie line
| being one of the first brown-field re-signaling jobs (not to
| mention a 24/7 railway), and then the program just seemed to
| languish under management that didn't see CBTC's value or the
| need for modernization (could write pages on this). Thankfully
| the new cadre of people at 2 Broadway has put the CBTC program
| into high gear, with 4 (5?) lines under various stages
| resignaling at the movement.
|
| As a bonus tidbit: the wheel slip issue mentioned above is
| fixed in CBTC operations with the inclusion of a free axle,
| equipped with no motor or breaks, thus never experiencing a
| lack of adhesion. Passive RFID balise's placed at known
| intervals (i.e. loaded into the train) allow the train to then
| audit (while in operation) how far its estimated position and
| speed have deviated from where it truly is. Some CBTC systems
| also have car-brone backups based on accelerometers or rail-
| facing doppler radars.
|
| [1] https://en.wikipedia.org/wiki/Communications-
| based_train_con...
| psychphysic wrote:
| I believe it is actually a hard problem but there is a good
| solution being explored on the UK.
|
| Read the rails like a card magstrip.
|
| Trains first traverse the track scanning the entire length in
| detail with careful speed and location tracking.
|
| Then trains can subsequently pattern match to the rail for
| location and speed.
|
| The rails can also be coded with info like patterns although
| that's not generally needed. Trains get loaded with info about
| the track they'll be on and then can monitor progress
| themselves.
| rightbyte wrote:
| > For example you can put a sensor on the electrical motor that
| will accurately measure motor position.
|
| That is a spring mass system. Oscillations at the motor might
| or might not move the wheels. You want to measure at the
| wheels.
|
| Also the play in the driveline messes up speed measurements.
| brutusborn wrote:
| My guesses: - Lack of incentives for executives to improve
| performance -Lack of people with good ideas to plan
| improvements -Lack of skills to execute an improvement plan
| (due to relatively low salaries) -Pointless regulation
| -Deferred maintenance to 'save money'
| ehnto wrote:
| Indeed, I can see this being a bureaucractic challenge more
| than a technical one.
|
| There are quite clear paths forward and no shortage of prior
| art for the engineering portion, unless there is something we
| aren't privvy to it must be lack of incentives and
| bureaucracy.
| rocqua wrote:
| My sense is that "we need 99.9% uptime so solutions that
| require maintenance downtime are not acceptable" even
| though the lack of solutions is a bigger drag on uptime.
| But if your mandate is uptime, voluntary downtime is not at
| all an easy choice. You get blamed for voluntary downtime
| whilst accidental downtime is not directly going to be
| blamed on anyone.
| jimmyswimmy wrote:
| While i agree that it is surprising that MTA continues to use
| archaic technology, I don't the solution is nearly as simple as
| you pose it. Hardware engineering is hard, and in-service
| engineering of complex systems desiring near 100% uptime is
| challenging.
|
| The sensors must not simply survive a dirty, dusty environment,
| they must work perfectly with no glitches and for long periods
| between maintenance. And if they do swap out for a different
| sensor system and it fails, there's no hardware equivalent of
| git reset --hard (the favored way for this hardware designer to
| undo my soft mistakes). You have to take a train out of
| service, or put people in the tracks during a maintenance
| window.
|
| What they have there already obviously also requires
| maintenance, but its performance limitations and failure modes
| are well understood. It takes time to cycle new things in, and
| old out.
|
| Nonetheless I was also fairly shocked that their system is
| quite as archaic as it is. I assume it's a budget limitation
| driving slow progress.
| hadlock wrote:
| My 1955 Citroen (designed in 1933) has the original
| speedometer and speed sender cable. It's accurate (GPS
| tracked) to within 2-3km/h. This is with nearly 70k miles on
| the clock. This is the same mechanism Citroen used in their
| 2CV from 1946 until 1992. Most Model A Fords from 1929 have
| their original speedometer (which works fine, might need
| greasing every few decades though). With tens of thousands of
| miles on them.
|
| We are way, WAY beyond "hardware engineering is hard", this
| is "this was a solved problem a century ago, using archaic
| means". I am happy to hand-wave away all sorts of problems
| but speedometers were 100% a solved problem many many years
| ago and no allowances or leeway should be given for this
| specific problem. Zero.
| pantalaimon wrote:
| GPS doesn't work underground though.
|
| But the problem described in the article seems rather
| unique to NYC and one has to ask how other subway systems
| manage just fine without artificial slowdowns.
| mvnuweucxqokii wrote:
| I'm pretty sure the person you're replying to was saying
| that the original speedometer mechanism in their 1955 car
| is accurate to within 2-3 km/h of the speed reported by
| GPS, and thus suggesting that this pre-GPS mechanism
| ought suffice for the subway / be better than whatever
| they currently use.
| vlovich123 wrote:
| You can simulate the GPS if you wanted to, drop cables
| down to pipe through the real signal, or simply do very
| basic positioning with custom radios underground.
|
| OP is correct. We have significantly better techniques.
| termy wrote:
| Go fix it then :p
| Symbiote wrote:
| For what it's worth, a metro train does around 100,000
| miles _per year_.
| vladvasiliu wrote:
| That's fair. And also, the environment is probably
| different, as in more dust in the tunnels, etc.
|
| But to stick with French technology, the Paris metro, for
| all its issues, does have working speed gauges. Some
| lines still use rolling stock from the 60s and 70s.
| phist_mcgee wrote:
| And every single one of them invariably is when i'm not
| onboard.
| Gordonjcp wrote:
| So, considerably less than the average articulated lorry,
| or indeed Skoda Octavia?
| Symbiote wrote:
| No, very much around the average for an articulated
| lorry.
|
| But metro trains stop and start every 2-5 minutes all
| day, last 40+ years, but also travel on a very smooth
| "road".
| gambiting wrote:
| So do most normal trains, and they all have speed gauges
| that work fine, rain snow or dust. Clearly the technology
| exists.
| akgerber wrote:
| NYCT was, until this year, operating R32 trainsets still
| limping along from the 1960s that were repeatedly life-
| extended as newer (1970s) train types experienced
| structural failures & delivery of their planned
| replacement trains was repeatedly delayed. It's obviously
| possible to maintain old trains, but generally expensive
| & challenging, especially when they're still doing
| 100,000 miles a year, and things clearly slipped.
|
| Especially because the trains were operating well past
| their planned lifespan because their replacements were
| ordered but not delivered, so the major overhaul that
| would that would normally be done to life-extend a train
| kept running for decades didn't happen.
| squeaky-clean wrote:
| They're slowly switching each line to a CBCT based signaling,
| the lines that do have it are vastly improved. Aside from all
| the budget and construction corruption issues of the MTA,
| it's difficult to do because the NYC subway is expected to
| run 24/7. And so upgrades need to be scheduled around limited
| times during which lines can be shut down, usually just a few
| hours overnight. And also keep the old system running while
| upgrades happen which tend to take years for a full line
| upgrade.
|
| https://en.m.wikipedia.org/wiki/Communications-
| based_train_c...
| ajsnigrutin wrote:
| So.. what tech do normal, above ground trains use?
| jazzyjackson wrote:
| > I assume it's a budget limitation driving slow progress.
|
| The budget is enormous, it's just being embezzled from top to
| bottom.
| interstice wrote:
| Is there a term for using multiple redundancy and statistics
| to solve issues, for example using 5x 99% reliable sensors
| rather than a single 99.99% sensor that costs 100x more?
| LikesPwsh wrote:
| "redundant systems"
| bdavis__ wrote:
| engineering
| steveBK123 wrote:
| Don't forget WET environment. Due to the closeness to the
| surface and the era most of the tunneling was done, there's
| not just high humidity but actual water in the tunnels and
| stations quite often.
| o10449366 wrote:
| Unfortunately, it's a pretty tired HN comment to posit
| something as being more simple than it actually is.
|
| Even during the pandemic there were widespread complaints
| about the signal work on the L line that has now transformed
| it from one of the worst lines to one of the best. There's no
| such thing as "simple work" on a system that millions of
| people depend on for consistent uptime.
| atoav wrote:
| If you count in the financial constrait that service is
| working under, sure. But meassuring the speed/position of a
| rail vehicle on a piece of track reliably is _not_ an
| unsolvable feat of hardware engineering. It is done
| elsewhere and it is done elsewhere where similar
| constraints for uptime exist.
|
| Theoretically by that logic we could argue that trains are
| hard because making the motors for them is non-trivial. It
| is non-trivial, and depending on your standards it might be
| even hard. But it is essentially a solved problem. You want
| a motor? You get one from the big companies, let them
| design one or use one from an existing similar train. Same
| thing goes for measuring speed. You want it? Create a team
| researching which ones to get.
|
| Like in many places NY infrastructure has it's best days
| long behind itself and it is a wonder it still works. That
| infrastructure is in dire need of modernization and it has
| been for a while. The reason this is not done is _not_
| because it is hard or impossible to do. It is just
| expensive.
| digbybk wrote:
| You're correct, it's not unsolvable, which is why it is
| being solved. It's just a slow process, for the reasons
| mentioned.
| draw_down wrote:
| [dead]
| scotty79 wrote:
| I just came up with silly calibration strategy for speedometer.
| When the train is on a curve of known radious you can get true
| speed from measured lateral acceleration.
| jawadch93 wrote:
| [dead]
| Tokkemon wrote:
| A part of this story is how during Andy Byford's tenure, one of
| the biggest thrusts to his work was to fix this problem. He
| aggressively started studying and revising the timers to speed
| trains up, and it seemed to have worked. Of course, he was pushed
| out by Cuomo and then the pandemic happened so much of those
| gains seem to be short-lived.
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