Ways we could make trains safer and smarter • Hacker News Board

Re: Ways we could make trains safer and smarter

#11

Post by matthewmacleod » Mon, May 08, 2017, 9:58 PM UTC

Animats wrote: post #7

matthewmacleod wrote: post #5

Earlier quoted context omitted.

You're right that track circuits are simple and relatively reliable, but they are also inefficient. Having to retain sufficient safety margins while being unaware of the real location of trains means that there is excess "dead space" in each signalling block that could be used to drive more trains over the existing infrastructure. It's what happens with systems like the DLR in London, which uses an advanced moving bl…

Few railroads run trains that tightly spaced. The London Underground and the NYC subways do have that problem, and they've both been cautious about installing newer train control systems. The London Underground's Victoria Line has a modern system, and it's been troublesome.[1] The enthusiasm for GPS-based systems comes from low-traffic railroads with a lot of track per train. Their maintenance cost for trackside equi…

From the article you cited:

A strong argument in favour of computerisation, however, is that the worst delay caused to trains in service as a result of these types of failure was 30 minutes long – with the mean average delay time across all 700+ automated system failures being just five minutes.

That is amazing. Bear in mind that the Victoria Line runs over 30 trains per hour in the peak! I don't feel that "troublesome" is an appropriate description.

In the UK at least, a large number of railway routes really are constrained by the safety margins required for trains. In the late 90s, when the West Coast Main Line was upgraded, there was an abortive attempt to implement a modern moving-block signalling system – but it was predictably too difficult for such a complex line.

I don't doubt that you're right about the incentives being different on low-traffic lines though. It does demonstrate that there are various benefits to more automation that need to be traded off against the complexity, cost, and rust of failures.

Re: Ways we could make trains safer and smarter

#12

Post by Animats » Mon, May 08, 2017, 9:59 PM UTC

mrbabbage wrote: post #8

Animats wrote: post #3

"A train equipped with positive train control uses GPS, Wi-Fi, and radio signals to find out what to expect on the track ahead, then figure out when it should start slowing down based on things like its own speed and weight." The existing 1920s track circuit technology is simple and reliable. The train's wheels short the rails together, cutting off power to a relay at the end of the block, which sets signals behind t…

The GPS, radio communication, etc., that the article talks about are not the important bits of positive train control IMO. The important bits are "positively" enforcing safety -- reaching a safe state even if a rail vehicle violates the instructions the signalling system provides it. America's PTC mandate was triggered by the tragic Chatsworth crash back in 2005 or so, which would have been prevented if the red signa…

NYC Subway is really hard-core about train stops. There's a trip cock on every subway car, near the right front wheel, and it works by directly operating an air valve to the brakes. The train stop lever alongside the track is raised by a big spring and lowered electrically, and the signaling system senses when it's physically up, ready to trip. Only then can the preceding train stop lower. There are always several train stops up between trains. A signaling failure or power cut will raise the train stops.

"The central principle of signal placement and engineering is that the control lengths of the signals be so designed such that when a train running at the highest possible speed under the worst weather conditions, with any semblance of functional brakes, is tripped, it will come to a halt before encountering the other train or obstruction that is causing the signal to be red."

Some signals have timers, for speed control. Go through a block too fast, and the signal ahead won't clear. Then the train stop will stop the train. This is common in downhill sections and ahead of curves.

Resetting a trip cock in NYC requires getting out of the cab and climbing down to the tracks. This is Not Fun.

Chicago has self-resetting trip cocks, which resulted in an accident in 2013.[1] A train parked in a service yard had a water leak into the control cables, which caused the train to move, slowly. The train hit a train stop, the brakes were applied, and the train stopped. But the trip cock reset, and the train started again. This happened five times at five different train stops. Workers noticed, but were not able to stop the train. This continued until the train hit an occupied but stopped train just outside the yard.

This is why you want dumb train control.

[1] https://www.ntsb.gov/investigations/AccidentReports/Reports/...

Re: Ways we could make trains safer and smarter

#13

Post by niftich » Mon, May 08, 2017, 10:00 PM UTC

matthewmacleod wrote: post #5

Animats wrote: post #3

"A train equipped with positive train control uses GPS, Wi-Fi, and radio signals to find out what to expect on the track ahead, then figure out when it should start slowing down based on things like its own speed and weight." The existing 1920s track circuit technology is simple and reliable. The train's wheels short the rails together, cutting off power to a relay at the end of the block, which sets signals behind t…

You're right that track circuits are simple and relatively reliable, but they are also inefficient. Having to retain sufficient safety margins while being unaware of the real location of trains means that there is excess "dead space" in each signalling block that could be used to drive more trains over the existing infrastructure. It's what happens with systems like the DLR in London, which uses an advanced moving bl…

So have tighter blocks more often.

A block is a discretization of the continuous track, and in track-space, your absolute "GPS" location isn't relevant -- just where you are on the track.

The on-vehicle location detector ("GPS") is essentially a cost-effective alternative to having infinitesimally small, fixed blocks.

The benefits are equivalent: the tradeoff is between whether you want to spend money on maintaining fixed trackside infrastructure, or more advanced equipment inside on-track vehicles.

Re: Ways we could make trains safer and smarter

#14

Post by notmtaemployee » Mon, May 08, 2017, 10:09 PM UTC

Animats wrote: post #12

mrbabbage wrote: post #8

Earlier quoted context omitted.

The GPS, radio communication, etc., that the article talks about are not the important bits of positive train control IMO. The important bits are "positively" enforcing safety -- reaching a safe state even if a rail vehicle violates the instructions the signalling system provides it. America's PTC mandate was triggered by the tragic Chatsworth crash back in 2005 or so, which would have been prevented if the red signa…

NYC Subway is really hard-core about train stops. There's a trip cock on every subway car, near the right front wheel, and it works by directly operating an air valve to the brakes. The train stop lever alongside the track is raised by a big spring and lowered electrically, and the signaling system senses when it's physically up, ready to trip. Only then can the preceding train stop lower. There are always several tr…

For what its worth you can run a red signal if you go slow enough over the trip, however doing this without approval from rcc will get you suspended or more

Re: Ways we could make trains safer and smarter

#15

Post by notmtaemployee » Mon, May 08, 2017, 10:23 PM UTC

niftich wrote: post #13

matthewmacleod wrote: post #5

Earlier quoted context omitted.

You're right that track circuits are simple and relatively reliable, but they are also inefficient. Having to retain sufficient safety margins while being unaware of the real location of trains means that there is excess "dead space" in each signalling block that could be used to drive more trains over the existing infrastructure. It's what happens with systems like the DLR in London, which uses an advanced moving bl…

So have tighter blocks more often. A block is a discretization of the continuous track, and in track-space, your absolute "GPS" location isn't relevant -- just where you are on the track. The on-vehicle location detector ("GPS") is essentially a cost-effective alternative to having infinitesimally small, fixed blocks. The benefits are equivalent: the tradeoff is between whether you want to spend money on maintaining…

Having more and tighter blocks is a distraction, it requires significant maintenance of way (MOW) resources and track time access which is limited to begin with in systems like New York.

The real solution is deploying moving block signals based on Communications-based train control (CBTC) which uses passive rfid balise's placed at known intervals and highly precise tachometers and odometers on the train. This allows any maintenance that needs to be conducted to be done offline, simply drive the train to the dedicated maintenance facility. With CBTC the only item needed to inspect on the right of way is radio system which can be done safely from the cat walk, ie. no need for track access or flagging.

This is what has been done for the Canarsie and Flushing Lines (except they also tie into the existing block signalling to support non cbtc compatible trains). CBTC allows for tighter headway's (more tph) and automatic train operation meaning reducing employe costs (trains drive themselves).

GPS is just a big distraction and should be avoided for mass transit and reserved basically for dark territory PTC.

Re: Ways we could make trains safer and smarter

#16

Post by mrbabbage » Mon, May 08, 2017, 10:29 PM UTC

Animats wrote: post #12

mrbabbage wrote: post #8

Earlier quoted context omitted.

The GPS, radio communication, etc., that the article talks about are not the important bits of positive train control IMO. The important bits are "positively" enforcing safety -- reaching a safe state even if a rail vehicle violates the instructions the signalling system provides it. America's PTC mandate was triggered by the tragic Chatsworth crash back in 2005 or so, which would have been prevented if the red signa…

NYC Subway is really hard-core about train stops. There's a trip cock on every subway car, near the right front wheel, and it works by directly operating an air valve to the brakes. The train stop lever alongside the track is raised by a big spring and lowered electrically, and the signaling system senses when it's physically up, ready to trip. Only then can the preceding train stop lower. There are always several tr…

WOW! That Chicago story is straight up bizarre. Thanks for sharing that.

I'm not sure, though, that dumb train control is necessarily the answer. The Chicago system looks pretty dumb (though I know nothing about it), certainly no more complex than the New York system, but the fact that the CTA system self-reset seems to imply it cannot be safe without a human in the cab. This misfeature is a problem regardless how dumb or complex the signal system is.

Also, my hometown has one of the world's first automatic train operation systems (BART), and to my knowledge it hasn't had a revenue service malfunction leading to a crash since October 2 1972, less than a month after it opened. However, the train control system did lead to a good deal of litigation and project timeline overruns. I think the take-home lesson is that brand new technology is extraordinarily painful to debug and deploy; it's always going to be better to re-use train control that someone else debugged on their railway rather than re-inventing the wheel for your project.

Re: Ways we could make trains safer and smarter

#17

Post by dheera » Mon, May 08, 2017, 10:33 PM UTC

Animats wrote: post #3

"A train equipped with positive train control uses GPS, Wi-Fi, and radio signals to find out what to expect on the track ahead, then figure out when it should start slowing down based on things like its own speed and weight." The existing 1920s track circuit technology is simple and reliable. The train's wheels short the rails together, cutting off power to a relay at the end of the block, which sets signals behind t…

I've always wondered if, in the age of high-speed bullet trains, it is possible to use the pair of rails as a transmission line, send a pulse down the track, and measure the distance to the next obstacle by the reflection.

Of course they use the rail as an electrical ground, though, which could be an issue.

Re: Ways we could make trains safer and smarter

#18

Post by derefr » Mon, May 08, 2017, 10:38 PM UTC

Animats wrote: post #3

"A train equipped with positive train control uses GPS, Wi-Fi, and radio signals to find out what to expect on the track ahead, then figure out when it should start slowing down based on things like its own speed and weight." The existing 1920s track circuit technology is simple and reliable. The train's wheels short the rails together, cutting off power to a relay at the end of the block, which sets signals behind t…

> There are later systems that still use track circuits, but provide more information to the driver and locomotive. These involve devices which sit between the rails and send signals to the train. Most of these are passive RFID-tag type devices. Some are wired into the signaling system.

Why do things this way, instead of just having the switches themselves notify control when they change state? (Or do they already?) That by itself tells you almost all you need to know about where a train is.

Re: Ways we could make trains safer and smarter

#19

Post by AnimalMuppet » Mon, May 08, 2017, 11:26 PM UTC

dheera wrote: post #17

Animats wrote: post #3

"A train equipped with positive train control uses GPS, Wi-Fi, and radio signals to find out what to expect on the track ahead, then figure out when it should start slowing down based on things like its own speed and weight." The existing 1920s track circuit technology is simple and reliable. The train's wheels short the rails together, cutting off power to a relay at the end of the block, which sets signals behind t…

I've always wondered if, in the age of high-speed bullet trains, it is possible to use the pair of rails as a transmission line, send a pulse down the track, and measure the distance to the next obstacle by the reflection. Of course they use the rail as an electrical ground, though, which could be an issue.

I don't see why you couldn't. You're basically describing a time-domain reflectometer.

But it is correct for you to say "to the next obstacle" rather than "to the train". The next obstacle could be a switch, or perhaps a line welded on for the signaling system. It could even be a broken rail.

Re: Ways we could make trains safer and smarter

#20

Post by inferiorhuman » Tue, May 09, 2017, 12:34 AM UTC

Animats wrote: post #7

matthewmacleod wrote: post #5

Earlier quoted context omitted.

You're right that track circuits are simple and relatively reliable, but they are also inefficient. Having to retain sufficient safety margins while being unaware of the real location of trains means that there is excess "dead space" in each signalling block that could be used to drive more trains over the existing infrastructure. It's what happens with systems like the DLR in London, which uses an advanced moving bl…

Few railroads run trains that tightly spaced. The London Underground and the NYC subways do have that problem, and they've both been cautious about installing newer train control systems. The London Underground's Victoria Line has a modern system, and it's been troublesome.[1] The enthusiasm for GPS-based systems comes from low-traffic railroads with a lot of track per train. Their maintenance cost for trackside equi…

SF's Muni also uses an advanced, communications-based moving block system. It too has been troublesome. OTOH when it (and the employees) works, it's amazing to see the trains move through the station maybe 15-20 seconds behind the previous train.