How we slowed the subway down
homesignalblog.wordpress.com
homesignalblog.wordpress.com
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.
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.
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.
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.
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.
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.
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.
OP is correct. We have significantly better techniques.
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.
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.
But metro trains stop and start every 2-5 minutes all day, last 40+ years, but also travel on a very smooth "road".
https://en.m.wikipedia.org/wiki/Communications-based_train_c...
The budget is enormous, it's just being embezzled from top to bottom.
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.
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.
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...
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.
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.
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
The answer is that they should improve the technology so that the system is safe and faster.
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.
Yes it can, and it's essential that we do it, because the alternative is a ruinous level of risk aversion.
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.
Was a total piece of cake in 2020, of course %)
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.”
Your point probably still holds though.
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.
People stop taking the subway when it takes too long. That not only increases traffic, it also saps the system of funding.
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.
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.
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.
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.
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"
As Low As Reasonably Practical
"Physical men, serving as lamposts. You’ve advocated it long enough—you’ve got what you wanted’" (pp. 875-76).
You're just a selfish npc
"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.
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.
https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussun...
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.
Before that, speed control only happened at discrete points along the lines of "speed must be lower than x kph after y seconds", so you could actually continue running at full speed for up to y seconds before tripping the train protection.
Meanwhile, the currently existing lines on the two pre-war Underground rapid transit systems in Germany (Hamburg and Berlin) are still using simple train stops, too (though they did at some point upgrade to magnetic/inductive train stops instead of the original mechanical train stop system).
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.
Yeah I can see how the knock on tailbacks and flow will make roads insane.
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.
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
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".
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.
Where is the NTSB (national transportation safety board) in all of this? You shouldn't have to search around for news reports to find out about when incidents took place on a transit system operated by the government.
If NYC isn't adequately investigating, cataloging, and dealing with these incidents, why isn't the NTSB doing anything about it?
While the article is very interesting from an engineering perspective, it boggles the mind that such a safety critical piece of infratstructure is allowed to operate in an opaque manner with little or no oversight.
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.
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.