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SimSig: Railway Signalling Simulations

simsig.co.uk

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Re: SimSig: Railway Signalling Simulations

#31

Post by londons_explore »

secondcoming wrote: post #19
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 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…

> 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 harder than the guaranteed minimum braking)

Re: SimSig: Railway Signalling Simulations

#32

Post by trainyperson »

secondcoming wrote: post #19
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 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…

The 1-minute (or less) headways on London Underground are precisely because of signal modernization over the past couple decades that has moved certain lines beyond purely fixed-block signaling.

Re: SimSig: Railway Signalling Simulations

#33

Post by thanzex »

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…

I think that's not something that can be avoided, unfortunately. Any number of things could cause a train to suddenly stop. A mechanical failure, derailment, collision, a wagon could get detached... On roads we have millions of vehicles, carrying on average a very small amount of people, around 1.5. For efficiency sake we have accepted the risk of staying within reaction distance instead of stopping distance between vehicles.

It is a tradeoff between the safety of lives on board and traffic requirements that is relatively easier to accept when the average number of people involved is low against massive speed and efficiency gains.

The same cannot be said for trains though. Modern trains carry upwards of 1000 passengers, often at high speeds and without all of the safety and retention systems built into modern cars.

Having one or multiple trains with this large amount of people onboard be involved in a sudden catastrophic accident is possibly not worth the efficiency gained by thess than one minute separation.

Unfortunately we cannot just think about a normal scenario of simple deceleration

Re: SimSig: Railway Signalling Simulations

#34

Post by lqet »

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…

It is not safe. If your train crashes into a truck, or derails, or explodes, all trains behind will crash into it if they are nearer than their own breaking distance. This is not possible in a classic block system: the block is freed only when the last carriage of the blocking train has left the block.

Re: SimSig: Railway Signalling Simulations

#35

Post by londons_explore »

Cthulhu_ wrote: post #29
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…

This puts a LOT of faith / confidence in and requirements on hardware and communications; while it all sounds good on paper / in your head / in theory, there's going to be a ton of practical issues that someone more qualified than me will be able to list. It's got the same energy as Musk advocating for Hyperloop and/or car tunnels by amortizing all the practical, cost, engineering, legal and safety considerations. Su…

The market for people transport is huge. Imagine the cost of all apartments in manhattan @ $3000/sq foot. Now imagine the cost of the same apartments built in upstate new york @ $250/sq foot.

A transit provider who can get people from a house in a rural area to manhattan in 15 mins can pocket that difference, which is huuuuge.

Re: SimSig: Railway Signalling Simulations

#36

Post by cmul »

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…

Imho, the major constraint for railways in most countries is policy, not technology. In the US and many large (surface area) countries, railways primarily serve for freight transportation and, to a shockingly underdeveloped degree, local commuters. In Europe legacy solutions and differences of national systems, planning guidelines and even power grid cause problems. Some nations' railways are extremely underfinanced and have been driven to the brink of collapse in the privatizations of the early 90s with more than 30 years of missed investments. The rollout of ETCS tries to remedy that and so do ERA/EUG/ERJU but the coffers of many nations are rather empty/respectively other interests weigh higher (subsidies for streets, automotive companies, aviation and other big buckets like farming).

Re: SimSig: Railway Signalling Simulations

#38

Post by garaetjjte »

londons_explore wrote: post #25
pixiemagic wrote: post #20

Earlier quoted context omitted.

What happens if there's some other reason to brake, such as an unreported fallen tree on the line ahead?

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'.

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

Re: SimSig: Railway Signalling Simulations

#39

Post by jcranmer »

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…

There are two things that control the ruling headway on a subway system. The first is platform dwell time. While a train is stopped at a station, you cannot let another train move into its position as if it was going to start moving on schedule, because it's actually quite likely that it won't. Given that platform dwell time is about 30s, and taking into account time needed to decelerate and accelerate to/from a stopped position, this limits minimum headways to about 1m.

Similarly, switch fouling time is another constraint: you don't want to move a switch while a train is allowed to path over it, in case the switch fails to switch. From what I've heard of existing urban systems, this leads to a minimum headway of ~90s, although I don't know how much of that is signal-induced padding.

The next thing to point out is that these are theoretical maximum density; the practical maximum operational usage is generally far less. Most subway systems have the physical capability of operating ~45TPH on a subway line, yet you'll notice that extremely few do. Moscow Metro has managed 40TPH on an unbranched line; branched lines struggle to get to 30TPH, and heavily reverse-branched systems like the DC Metro or NYC Subway struggle to make even 20TPH. Introduce branches into the mix, and you need trains to make it onto the mainline in slots, and there's going to be variance in arrival time because the system is used by humans; reverse branches makes the problem worse because these slots need to line up well on multiple lines at the same time.

> Trains would be able to hitch and unhitch whilst moving 100 mph, allowing different loads to be sent different directions and different sets of passengers to stop at different stations.

No. There's a reason railroads have banned the practice of unhitching at speed (it's incredibly dangerous), and hitching is even worse. And if you're talking about EMU passenger train sets, most of them are designed to not be hitched or unhitched particularly frequently--these aren't your standard automatic coupler system (which doesn't couple brake lines or electrical lines or other things automatically anyways, FWIW).

Re: SimSig: Railway Signalling Simulations

#40

Post by londons_explore »

garaetjjte wrote: post #38
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'.

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.

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