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How we slowed the subway down

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Re: How we slowed the subway down

#61

Post by rocqua »

ehnto wrote: post #27
brutusborn wrote: post #24

Earlier quoted context omitted.

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’

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.

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.

Re: How we slowed the subway down

#62

Post by rocqua »

hristov wrote: post #5
dzdt wrote: post #3

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…

"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.

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.

Re: How we slowed the subway down

#63

Post by fukutyphoo »

hristov wrote: post #5
dzdt wrote: post #3

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…

"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.

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"

Re: How we slowed the subway down

#64

Post by rocqua »

maria2 wrote: post #6
hristov wrote: post #5

Earlier quoted context omitted.

"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.

Many lifetimes of time are being wasted every day to save < 10 lives every century.

What death risk are you talking about? Seems like an interesting anecdote.

Re: How we slowed the subway down

#65

Post by scotty79 »

hristov wrote: post #12

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 electri…

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.

Re: How we slowed the subway down

#66

Post by rocqua »

lifeisstillgood wrote: post #58

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.

Re: How we slowed the subway down

#67

Post by draw_down »

o10449366 wrote: post #38
jimmyswimmy wrote: post #35

Earlier quoted context omitted.

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…

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.

[dead]

Re: How we slowed the subway down

#68

Post by rocqua »

breck wrote: post #50

tldr;?

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.

Re: How we slowed the subway down

#69

Post by lifeisstillgood »

rocqua wrote: post #66
lifeisstillgood wrote: post #58

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.

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

Re: How we slowed the subway down

#70

Post by usr1106 »

pantalaimon wrote: post #44
tgsovlerkhgsel wrote: post #2

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-cur…

PZB was already introduced in 1934 https://en.m.wikipedia.org/wiki/Punktförmige_Zugbeeinflussun...

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.

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