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.
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.
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.
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’
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.
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.
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.
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.
"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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
> Collisions happened more frequently than they do today, but they generally did not kill. And while there exist news reports of incidents that sound suspiciously like signal system design issues – for example, a B train which rear-ended the system’s revenue collection train in Brooklyn in 1968 – these seem to have been rare. Most of the accidents whose stories made it into the press seemingly had little to do with signal system’s deficiencies.
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.
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.
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)
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.
[+] [-] hristov|3 years ago|reply
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.
[+] [-] jimmyswimmy|3 years ago|reply
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.
[+] [-] woodruffw|3 years ago|reply
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.
[+] [-] brutusborn|3 years ago|reply
[+] [-] psychphysic|3 years ago|reply
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.
[+] [-] scotty79|3 years ago|reply
[+] [-] notmtaemployee|3 years ago|reply
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...
[+] [-] rightbyte|3 years ago|reply
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.
[+] [-] dzdt|3 years ago|reply
[+] [-] hristov|3 years ago|reply
The answer is that they should improve the technology so that the system is safe and faster.
[+] [-] rtpg|3 years ago|reply
"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.
[+] [-] poslathian|3 years ago|reply
[+] [-] joe_the_user|3 years ago|reply
[+] [-] thrashh|3 years ago|reply
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
[+] [-] nkrisc|3 years ago|reply
[+] [-] themitigating|3 years ago|reply
You're just a selfish npc
[+] [-] tgsovlerkhgsel|3 years ago|reply
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|3 years ago|reply
https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussun...
[+] [-] mildchalupa|3 years ago|reply
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|3 years ago|reply
[+] [-] Tokkemon|3 years ago|reply
[+] [-] lifeisstillgood|3 years ago|reply
Yeah I can see how the knock on tailbacks and flow will make roads insane.
[+] [-] rocqua|3 years ago|reply
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.
[+] [-] tomohawk|3 years ago|reply
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.
[+] [-] danbmil99|3 years ago|reply
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.
[+] [-] kylehotchkiss|3 years ago|reply
[+] [-] valyagolev|3 years ago|reply
[+] [-] jawadch93|3 years ago|reply
[deleted]
[+] [-] breck|3 years ago|reply
[+] [-] rocqua|3 years ago|reply
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.