How does Network Rail work out max speeds?

[markymark2000]

I've blown a few speeds in my years. Sometimes it can't be helped. I've even been asked to deliberately blow an ESR to test for comfort and operational issues...

What you need to allow for is that once, isn't usually an issue. Going +5 every single day, multiple times a day could be a potential issue. A single test train isn't a proper stress test. There needs to be some kind of engineering allowance or limits of tolerance. I would assume that this is one of those 80 reasons.

One train is a step towards multiple trains per day testing it. If there are issues with the test train with signal sightings or something, no other trains get tested. If it works though on the test train(s), see if other trains can be done.

A very common mistake. Much of the railway is effectively at (or near) capacity, such that an increase in line speeds just means that the fast trains catch up the stopping trains earlier, and there is no journey time improvement.

In some cases, yes. There are many places though where service levels are much lower (half hourly or less) and any speed increase would lead to journey time reductions. Increasing the speed through Deansgate to Piccadilly will do sod all for anyone. The North Wales Coast though (The line works for the example, not saying any improvements could be made here) has trains fairly well spaced out and any speed increase wouldn't lead to fast trains catching up to slower ones.

It’s all more complex. A lot more complex. I assume you haven’t actually done his for real. I have, many many times.

Everything is complex, doesn't mean it is impossible.

 

[Bald Rick]

Everything is complex, doesn't mean it is impossible.

Of course it’s not impossible, which is why linespeeds have been raised in many, many places. However it takes a lot of smart people some time to work it all out. Time = money. Someone needs to pay. For someone to pay, they will want to get their money back or equivalent benefit. Someone needs to work that out.

Some of the effects of higher speed are felt in the long term (10 years+). Underbridge resonance effects for example. Ballast deterioration. High rail wear. All this needs to be worked out.

 

[DerekC]

One advantage of "moving block" signalling is that you don't have to worry about block length and capacity when calculating line speed. Obviously the other infrastructure constraints still apply, but that can still be a significant advantage.

 

[Domh245]

One advantage of "moving block" signalling is that you don't have to worry about block length and capacity when calculating line speed. Obviously the other infrastructure constraints still apply, but that can still be a significant advantage.

Surely though the faster the train is going the longer it's braking curve will be, meaning that it will have to run further behind the train in front than if it were a lower speed? Whilst it may not have as much of an impact as with fixed blocks, increasing the speed will still decrease the capacity

 

[DerekC]

Surely though the faster the train is going the longer it's braking curve will be, meaning that it will have to run further behind the train in front than if it were a lower speed? Whilst it may not have as much of an impact as with fixed blocks, increasing the speed will still decrease the capacity

Absolutely right - but the point is that when designing the signalling system you don't have to decide what speed/capacity combination you are designing for, then build it in to the block layout which fixes it for the next thirty years or so.

 

[Bald Rick]

One advantage of "moving block" signalling is that you don't have to worry about block length and capacity when calculating line speed. Obviously the other infrastructure constraints still apply, but that can still be a significant advantage.

Any type of full cab signalling means you don’t have to worry about block length, or indeed any signalling constraint, when it comes to linespeed. No concerns about signal sighting, spacing, approach control, diverging differentials, signal overrun risk, etc.

 

[RLBH]

Any type of full cab signalling means you don’t have to worry about block length

Not quite true - some types of cab signalling are definitely based on physical blocks, they just use lineside infrastructure to relay an indication to the cab of the signal aspect. The Irish CAWS system works along these lines.

In fact, AWS is arguably a very crude type of two-aspect cab signalling, and SRAWS was a three-aspect version. You wouldn't want to run a railway on either system alone, of course - as you can't clear a signal set to danger without passing it - but they do offer the core function of indicating whether to stop ahead of the next block or to proceed.

 

[Bald Rick]

Not quite true - some types of cab signalling are definitely based on physical blocks, they just use lineside infrastructure to relay an indication to the cab of the signal aspect. The Irish CAWS system works along these lines.

In fact, AWS is arguably a very crude type of two-aspect cab signalling, and SRAWS was a three-aspect version. You wouldn't want to run a railway on either system alone, of course - as you can't clear a signal set to danger without passing it - but they do offer the core function of indicating whether to stop ahead of the next block or to proceed.

Ah, I didn’t explain myself well. What I mean is that under any ‘speed based’ cab signalling system (which current systems are), block length need not be a determinant of Linespeed, as the signalling system is not restricted to the number of ‘blocks free’ that can be indicated by an external signal.

 

[reddragon]

The location is allegedly over the Weaver viaduct west of Northwich station, a half-mile stretch of 20mph which supposedly could be higher.
Pacers will be gone shortly, of course.

One issue is when the frequency of the train movement matches that of the structure. You get it with OLE and multiple pantographs and structures with trains. Structures can be affected by train speeds, and pacers have a unique movement frequency. Also tampers are banned on some structures for the same reason.