12 ms·

How we slowed the subway down

277 points by gok 4y ago

tgsovlerkhgsel 4y ago
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/MTA-to-test-energy-reduction-technology-on-subway-system--55935 https://www.progressiverailroading.com/sustainability/news/M...) despite the heat issues in the stations, I guess that's expecting too much.
- pantalaimon 4y ago
  PZB was already introduced in 1934 https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussung https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussun...
  - usr1106 4y ago
    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.
    - iggldiggl 4y ago
      Supervision of actual braking curves through PZB was actually only introduced starting in the mid-80s (first version of the PZB implemented through microprocessors), and widespread retrofitting of older rolling stock with an upgraded PZB-version only began in the late 1990s/early 2000s in response to the Rüsselsheim rail crash. 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).
dzdt 4y ago
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 4y ago
  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 4y ago
    For those wondering:https://en.m.wikipedia.org/wiki/ALARP https://en.m.wikipedia.org/wiki/ALARP As Low As Reasonably Practical
- thrashh 4y ago
  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
- hristov 4y ago
  "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.
  - maria2 4y ago
    Many lifetimes of time are being wasted every day to save < 10 lives every century.
hristov 4y ago
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.
- brutusborn 4y ago
  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 4y ago
    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 4y ago
      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.
mildchalupa 4y ago
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 4y ago
  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 4y ago
    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 4y ago
    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.
jawadch93 4y ago
[dead]
breck 4y ago
tldr;?
- rocqua 4y ago
  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.
lifeisstillgood 4y ago
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 4y ago
  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 4y ago
    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 4y ago
      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".
      - 4y ago
Tokkemon 4y ago
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.
kylehotchkiss 4y ago
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)
valyagolev 4y ago
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
danbmil99 4y ago
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.
tomohawk 4y ago
> 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.

277 points by gok 4y ago

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/MTA-to-test-energy-reduction-technology-on-subway-system--55935 https://www.progressiverailroading.com/sustainability/news/M...) despite the heat issues in the stations, I guess that's expecting too much.

pantalaimon 4y ago
PZB was already introduced in 1934 https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussung https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussun...
- usr1106 4y ago
  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.
  - iggldiggl 4y ago
    Supervision of actual braking curves through PZB was actually only introduced starting in the mid-80s (first version of the PZB implemented through microprocessors), and widespread retrofitting of older rolling stock with an upgraded PZB-version only began in the late 1990s/early 2000s in response to the Rüsselsheim rail crash. 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).

dzdt 4y ago

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 4y ago
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 4y ago
  For those wondering:https://en.m.wikipedia.org/wiki/ALARP https://en.m.wikipedia.org/wiki/ALARP As Low As Reasonably Practical
thrashh 4y ago
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
hristov 4y ago
"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.
- maria2 4y ago
  Many lifetimes of time are being wasted every day to save < 10 lives every century.

hristov 4y ago

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.

brutusborn 4y ago
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 4y ago
  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 4y ago
    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.

mildchalupa 4y ago

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 4y ago
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 4y ago
  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 4y ago
  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.

jawadch93 4y ago

[dead]

breck 4y ago

tldr;?

rocqua 4y ago
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.

lifeisstillgood 4y ago

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 4y ago
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 4y ago
  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 4y ago
    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".
    - 4y ago

Tokkemon 4y ago

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.

kylehotchkiss 4y ago

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)

valyagolev 4y ago

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

danbmil99 4y ago

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.

tomohawk 4y ago

> 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.