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SimSig: Railway Signalling Simulations

simsig.co.uk

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Re: SimSig: Railway Signalling Simulations

#71

Post by divingdragon »

londons_explore wrote: post #12

Railway signalling IMO is an area where a little research could dramatically increase the throughput of the railway network with a rather low cost. Todays railways mostly use fixed block signalling. Expensive and unreliable equipment ensures that there is only one train on each 'block' of railway track at the same time. That forces trains to be at least 1 or 2 blocks apart, which are frequently multiple miles long. E…

> Crashes would be avoided by having every train know about the train ahead and behind, and unable to make any move which would cause a collision (ie. it is not allowed to slam the brakes on if there is a train right behind you).

You are assuming that a train will never have to suddenly stop. This will never fly in the real world. Even if you consider a completely closed railway system with no possibility of external obstructions, there are many kinds of failure that would cause modern trains to apply emergency breaks due to fail-safe designs.

If you remove the bit about not allowing to slam on the breaks, then you just described SelTrac. Even the first version used on the Vancouver SkyTrain (opened in the 80s) is capable of running trains closer than braking distance from what I remember reading. I don't believe it is actually enabled on many SelTrac systems though, because you still need to have safety margins. There is always the possibility that the train in front may decelerate at a rate higher than its emergency braking rate, like if it derailed or collided with external obstructions.

Re: SimSig: Railway Signalling Simulations

#73

Post by TylerE »

trainyperson wrote: post #23
londons_explore wrote: post #12

Railway signalling IMO is an area where a little research could dramatically increase the throughput of the railway network with a rather low cost. Todays railways mostly use fixed block signalling. Expensive and unreliable equipment ensures that there is only one train on each 'block' of railway track at the same time. That forces trains to be at least 1 or 2 blocks apart, which are frequently multiple miles long. E…

Much of what you’re describing (besides the live hitching and unhitching) is made possible by Communication-Based Train Control (CBTC) [see link below]. This has been implemented in many rail systems globally, mostly urban rail. It helps reduce headways a lot . However: 1. It’s not just a software problem - installing the hardware is time-consuming and expensive. The engineering requirements are much stricter when hu…

Urban systems are generally single-user networks, which makes life a lot easier. For main line railways that assumption doesn't hold, which is where things kinda fall apart.

It's a bit like the old copypasta from the slashdot days of "This is why your solution to spam won't work", where one of the options was "It requires the entire internet to change at once.

Just look at what a big deal in the US it was to get positive train control (PTC) installed nationally.. and that's a much simpler system that is basically local (Picks up info from relays in the track, but all the logic is in the locomotive).

Re: SimSig: Railway Signalling Simulations

#74

Post by ChoHag »

mezmor wrote: post #21
londons_explore wrote: post #16

Earlier quoted context omitted.

This still doesn't allow train spacing of less than the braking distance. Braking distance of trains is large (due to high uncertainty in track friction), which still means trains are typically 1 minute or more apart when moving fast. As long as you have comms with the trains around, it's clearly possible to safely go less than the braking distance, as long as you can be sure of the behaviour of the train ahead, even…

Aren't braking distances so large because of the massive amounts of mass in motion? Inertia, etc. Even high certainty of track friction wouldn't change that. Also, I don't think it's ever safe to be closer than braking distance because the bahavior of the train ahead is never guaranteed. There's always a chance somebody parks their car on a rail crossing or some other sudden stopping-event occurs.

[dead]

Re: SimSig: Railway Signalling Simulations

#75

Post by ChoHag »

euroderf wrote: post #22
secondcoming wrote: post #19

Earlier quoted context omitted.

> Crashes would be avoided by having every train know about the train ahead and behind Isn't this a block system? > it is not allowed to slam the brakes on if there is a train right behind you So if we have three trains in close succession and the first derails or loses power, the second is not allowed stop because there's a train behind it? > Trains are usually 10's of minutes apart, or at least 1 minute apart even…

AFAIK the underground is not beset with blockages caused by fallen trees and stalled automobiles.

[dead]

Re: SimSig: Railway Signalling Simulations

#76

Post by TylerE »

danhor wrote: post #48
londons_explore wrote: post #25

Earlier quoted context omitted.

You can still brake - you just need (automatic) agreement of all trains behind you to do so. You aren't allowed to brake 'as much as possible' anymore - instead the best you can achieve is 'the best the worst of the trains behind me can achieve'.

You could also characterize the maximum braking ability of the train in front of you and the minimum braking ability of your own train and determine the needed distance for any given speed based on that. This would of course be more complicated and probably be solved by only including broad categories of trains (i.e. only two sets of values for either passenger trains or freight trains).

You also would need to consider the braking ability of the train BEHIND you.

Re: SimSig: Railway Signalling Simulations

#77

Post by TylerE »

danhor wrote: post #66
TylerE wrote: post #64

Earlier quoted context omitted.

Trams often have rubber tires, which gravely increases acceleration and braking. Also, 80m isn’t that long. Trains on the the DC metro are pushing 200. 8 cars long.

> Trams often have rubber tires No, they don't. There are a handful of weird french systems (and even less outside of France), but there are more ruber-tire metros than trams, I'm sure. They are rare and have been getting rarer. 80m is in the lower half for metros, but long in the context of systems having on-street portions (exceeding the german legal limit of 75m with a special exception). It's also on the long end…

The Stuttgart system is light rail, not a tram. Big difference.

Re: SimSig: Railway Signalling Simulations

#78

Post by marksomnian »

class700 wrote: post #11
amouat wrote: post #7

Earlier quoted context omitted.

Also traksy e.g: https://traksy.uk/live/T+EDB+KGX+d+@2024-07-10T13:00/M+1+EDI...

There's also OpenTrainTimes https://www.opentraintimes.com/maps/signalling/wat#T_WATRLMN And https://www.realtimetrains.co.uk/ for precise times/platform information.

And https://www.map.signalbox.io/, which tries to interpolate signal locations onto a geographic map (with the expected level of inaccuracy, though still not half-bad)

Re: SimSig: Railway Signalling Simulations

#79

Post by marksomnian »

cmul wrote: post #59
secondcoming wrote: post #24

Earlier quoted context omitted.

It does have its fair share of 'people under a train' and people preventing doors from closing.

Which is why ATO (automatic train operation) is most often found in subways where the platforms can be equipped with gates to keep passengers out until a train has stopped safely. Suicide by train and level crossings are a nightmare in risk management for railway safety, hence also (new) high speed tracks are usually planned without any intersections with roads or paths, at respective additional costs.

Some lines on the London Underground do use ATO without platform barriers. The driver closes the doors, checks that the platform is clear, then starts the train. ATO takes over until the next station, where the driver watches to make sure there's nobody too close to the edge, ready to slam on the emergency brake.

Re: SimSig: Railway Signalling Simulations

#80

Post by andbberger »

londons_explore wrote: post #16
dividuum wrote: post #13

Earlier quoted context omitted.

> A more advanced system would aim to have trains as close together as cars are on a freeway. https://en.wikipedia.org/wiki/European_Train_Control_System#...

This still doesn't allow train spacing of less than the braking distance. Braking distance of trains is large (due to high uncertainty in track friction), which still means trains are typically 1 minute or more apart when moving fast. As long as you have comms with the trains around, it's clearly possible to safely go less than the braking distance, as long as you can be sure of the behaviour of the train ahead, even…

this is decidely a feature and not a bug. CBTC systems work by continually updating track leases to the last known position. this allows for high throughput while safely avoiding collisions in case of catastrophe.

highway separation is unacceptable for anything other than trams (which are slow and have track brakes). the path to safely increasing throughput is to increase braking performance and minimize dwell time. existing systems eg paris line 14 and the tokaido shinkansen have very high throughput.

transit projects would look even better compared to highways if they had to be safe too!

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