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SimSig: Railway Signalling Simulations

simsig.co.uk

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Re: SimSig: Railway Signalling Simulations

#81

Post by bryananderson »

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…

As others have pointed out, most of this is a good idea and already exists in the form of moving-block communications-based train control which is used all over the world.

The parts that don’t exist—traveling closer than the stopping distance and hitching/unhitching at speed—are not good ideas unfortunately.

You can’t travel closer than the stopping distance because you can’t guarantee that the train ahead will stop at its own achievable stopping distance. If you could, you could do as you describe, and have the next train start braking instantly when the one ahead brakes. But striking an unexpected obstacle and/or derailing can cause the train ahead to stop quite a bit more abruptly than that! If the train ahead suffers some kind of violent failure, it could leave sizable debris and/or track damage at the point of the event, even if most of the train continues along for some distance. So, even with moving-block CBTC, you must always be capable of stopping before reaching the current location of the train ahead of you.

Anyway it is not really necessary to travel so closely together, because the limiting factor of throughput is station dwell time. Sure you could have huge throughput on a line with no stations if you could theoretically travel at car-on-highway spacing, but if you have stations and they can only serve one train at a time, you won’t gain anything by doing this. You can improve this by having a platform with a track on each side so you can load two trains at once (and this is pretty common when dwell time is really long and throughput must be high, i.e. for intercity trains on a busy line), but that is the best you can do. You can’t really scale this to a bunch of platform tracks because you’ll start to have merging conflicts when rejoining the track.

The problem with unhitching at speed follows naturally from the problem with close following: the moment you unhitch, you are now following too closely behind another train, and you cannot stop in time if something bad happens to it.

Re: SimSig: Railway Signalling Simulations

#82

Post by blibble »

londons_explore wrote: post #40
garaetjjte wrote: post #38

Earlier quoted context omitted.

If one train derails for some reason, then every single train on the line crashes in the greatest pileup ever. Great.

Thats already the case for carriages within a train.... And people are fine with it. We're also fine with the risk of a derailment onto a neighbouring track with traffic going the opposite direction. We could have tech which detects that, but we do not.

one of the original tube line ATO systems allowed a train to enter a platform as another was departing

people did not seeing this and the system was modified to not do it

Re: SimSig: Railway Signalling Simulations

#83

Post by TylerE »

bluGill wrote: post #26
londons_explore wrote: post #18

Earlier quoted context omitted.

Moving block doesn't allow trains to get closer together than the braking distance. This would.

There is good reason they don't do that: trains derail once in a while, your plan means the following train will hit that train and so the accident is worse. Part of the answer to that is better track maintenance. However that isn't a perfect answer and so we need larger gaps. Note that cars on the freeway are normally much closer together than is safe as well. If cars maintained a safe following distance we would ne…

I'm not even sure derailments is the worst flaw.

As soon as one train has to slow down, you're going to get the mother of all cascading effects - trains are slow to brake, but their acceleration is quite a bit slower than that, and you'll be limited to, at the very best, the acceleration of the slowest train in front of you.

Re: SimSig: Railway Signalling Simulations

#84

Post by numpad0 »

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…

looking for what hasn't yet said here...

- some lines like Yamanote already use mobile block, 1 minute headways is pretty much SoTA with or without it.

- some systems like surface trams and AGTs can stop on a dime, but they are low efficiency, low capacity systems.

- trains scale well, the longest freight train known to man so far is ~4.5 miles long. A typical 15-car ~2k passenger commuter trains stretch about 300m(0.2mi).

- Just napkin math in loud: each Yamanote train at typical 150% capacity running at 1-minute headways can transport 2k[pax] * 60[min] = 120k passengers per hour per train; Yamanote has 30 stations with at at least one each of CW and CCW platforms; 120k * 30 stations is already 3.6m passenger per hour combined, or 28.8m per 8 hour day. Hypothetically the train can be joined back to back, operated 16 hours per day, tracks can be doubled, for a 2^3 multiplier to 28.8m figure. That's 230.8m/day or about 67.5% US population worth of traffic from just four pair of rails, and that's technically feasible with current technology. The question is how to make bucks out of it(build pairs of one Disneyland and a highrise apartment complex each along the rails)

Re: SimSig: Railway Signalling Simulations

#85

Post by andbberger »

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).

this is how CBTC works

Re: SimSig: Railway Signalling Simulations

#86

Post by TylerE »

Cthulhu_ wrote: post #54
chin7an wrote: post #17

Earlier quoted context omitted.

Is it Sweet Transit? The about section mentions that the developer was part of Factorio. Edit to add link - https://www.sweettransitgame.com/

It even looks like the rail assets were lifted straight from Factorio. I mean if it's all above board it's fine - Factorio's train system is really good. That said, they're also giving it major updates/overhauls in the upcoming update, so this one would be falling behind if there's no good relationships between the two.

The mechanics or more or less entirely unlike factorio. It’s this really weird city sim / train game hybrid that is pretty crappy at both halves.

Re: SimSig: Railway Signalling Simulations

#87

Post by febusravenga »

corobo wrote: post #57
londons_explore wrote: post #31

Earlier quoted context omitted.

> 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? The second is allowed to follow the 'train ahead derailed' plan, which presumably will involve stopping at a rate that the third train can also achieve. If comms is maintained during the event, new plans can also be made that are maybe better (eg. maybe try to brake…

Instead of a derailed train and a couple delayed trains you now have a derailed train and a couple of trains with flat wheels that also need clearing up (assuming they avoided slamming into each other) Definitely not sold on the "let's chuck out the failsafe method of railwaying" idea, haha

Interesting. Never thought about that, but are you saying that emergency brake on train tears wheels so much that it's not able operate normally? Interesting learn.

(the whole thread started by overconfident guy with unrealistic ideas ended as very informative, so actually net plus, who would thought)

Re: SimSig: Railway Signalling Simulations

#88

Post by TylerE »

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.

No, they’re very long because steel wheel on steel rail has much much much lower coefficient of friction than rubber on asphalt. If they brakes any harder they wheels would just lock up and skid, both running the wheels AND taking longer to stop than a normal braking application.

Re: SimSig: Railway Signalling Simulations

#89

Post by p_l »

febusravenga wrote: post #87
corobo wrote: post #57

Earlier quoted context omitted.

Instead of a derailed train and a couple delayed trains you now have a derailed train and a couple of trains with flat wheels that also need clearing up (assuming they avoided slamming into each other) Definitely not sold on the "let's chuck out the failsafe method of railwaying" idea, haha

Interesting. Never thought about that, but are you saying that emergency brake on train tears wheels so much that it's not able operate normally? Interesting learn. (the whole thread started by overconfident guy with unrealistic ideas ended as very informative, so actually net plus, who would thought)

While it won't guarantee such level of destruction, emergency braking generally involves breaking beyond normal usability limits - including allowing for effective destruction of components in process
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