How are speed limits set?

[John Smith 19]

We do, and (for example) Eastern Region knew how back in the 70s, but I'm not really sure what your point is.

That raising average speeds of trains, rather than the maximum should be a goal.

If you're referring to Birmingham-Manchester again, by the time you've made 5 stops and got through the Birmingham-Wolverhampton section that's added 25mim to a theoretical nonstop time. Then there's awkward restrictions at Stafford, Stone, Congleton and Cheadle Hulme... there was another at Norton Bridge but NR spent a vast amount to improve the junction there.

Given how much cash has been pumped into HS2 and AFAIK still without a mile of track being laid I'm reluctant to call any amount NR has spend on line upgrades "vast"

Agreed - so a 75mph freight and a stopping passenger maintain similar times.

I think you have misunderstood. The 60s issues were about short-wheelbase 4-wheel wagons, which (among other things) didn't take kindly to continuous welded rail and to higher speeds. A great deal of work went into producing freight stock that would perform well at 75mph (leading BTW to the Pacer railbus!).

and in fact now freight could perform considerably better than that. I've read partial studies suggesting 90mph is viable already. The suggestion was that "passenger speed - 10mph" could be a viable rule-of-thumb, rather than 2/3's of passenger speed that seems to be common.

And no (?) UK freight is timed for anything less than 60mph, while intermodals are 75mph typically.

Not sure brake technology is the issue so much as vehicle performance.

Isn't signalling all about stopping limits? Of course those limits have to accommodate worst case aged rolling stock but how old is the oldest UK rolling stock now?

And the freight operators would be pushing for limits to be relaxed if there was an engineering and business case. And for better pathing so they didn't sit in loops for hours. But rebuilding junctions or whole sections of line for higher speed is expensive and disruptive - hence the idea of building new lines....

Agreed, but like electrification there is a case for a rolling programme of review and upgrade.

PS welcome to the forum!

Thank you. It's nice to be welcomed, rather than doing the welcoming.

 

[Irascible]

and in fact now freight could perform considerably better than that. I've read partial studies suggesting 90mph is viable already. The suggestion was that "passenger speed - 10mph" could be a viable rule-of-thumb, rather than 2/3's of passenger speed that seems to be common.

Technically possible doesn't make it a good idea - there are rapidly growing aerodynamic issues going faster than we are with not very aerodynamic loads ( like boxes made of flat sides with gaps between them, for instance ), and the energy use scales rapidly too. If you're not using diesel you can at least theoretically recover a lot of the energy put into increased initial acceleration, if not the later drag.

Better acceleration & not having to leave trains looped for hours because they can't get up to linespeed fast enough to not use an extra path would do even more to increase average speed than going to 90mph...

 

[Ken H]

Technically possible doesn't make it a good idea - there are rapidly growing aerodynamic issues going faster than we are with not very aerodynamic loads ( like boxes made of flat sides with gaps between them, for instance ), and the energy use scales rapidly too. If you're not using diesel you can at least theoretically recover a lot of the energy put into increased initial acceleration, if not the later drag.

Better acceleration & not having to leave trains looped for hours because they can't get up to linespeed fast enough to not use an extra path would do even more to increase average speed than going to 90mph...

Better speeds at the pointwork at the ends of loops would help.

 

[Bald Rick]

There are some bery significant issues with intermodals travelling at (say) 90mph, not least power supply and the aerodynamic effect at station platforms. The mythical sign at Penrith that said ‘please stand behind the yellow line or you will be sucked off’ may have to be reinstated…

 

[brad465]

The drivers you are speaking to are either winding you up, or not competent. The speed on departure from every platform at Birmingham New St is 10mph, and has been for over half a century.

I'm guessing raising that speed would be too expensive and/or disruptive to conduct, or physically impossible, given how it hasn't been done yet even though a significant number of services would benefit from it. I remember over 10 years ago the sharp bend on the approach to Dover Priory passing the former junctions to Dover Marine was 10mph, but work was done to raise it to 20mph, but then that's a much simpler and less disruptive to complete example.

Many years ago I asked on here why 85mph was a relatively common top line speed for a relatively odd number, as opposed to pushing for 90 or settling for 80? One of the key answers that came out was the boundary between 85 and 90 was a notable one for safety standards IIRC.

 

[Bald Rick]

I'm guessing raising that speed would be too expensive and/or disruptive to conduct, given how it hasn't been done yet even though a significant number of services would benefit from it. I remember over 10 years ago the sharp bend on the approach to Dover Priory passing the former junctions to Dover Marine was 10mph, but work was done to raise it to 20mph, but then that's a much simpler and less disruptive to complete example.

Many years ago I asked on here why 85mph was a relatively common top line speed for a relatively odd number, as opposed to pushing for 90 or settling for 80? One of the key answers that came out was the boundary between 85 and 90 was a notable one for safety standards IIRC.

Departure from New St towards Proof House Jn was to be lifted after the resignalling - the track, electrification and everything else is fit for 20mph. I don’t know why it didn’t happen.

Track maintenance standards change at 90mph.

 

[30907]

Departure from New St towards Proof House Jn was to be lifted after the resignalling - the track, electrification and everything else is fit for 20mph. I don’t know why it didn’t happen.

Track maintenance standards change at 90mph.

85 was the BR(S) default limit for (steam-)loco-hauled trains so will have carried over unless a higher limit was specifically introduced.

 

[LMS 4F]

In 1976 I worked at Castleford and my beat included the station. On one occasion I saw a man with a radar speed gun checking train speeds, freight only as the passengers reversed even then. Never seen it since and no doubt is carried out much more automatically nowadays.

 

[Bald Rick]

In 1976 I worked at Castleford and my beat included the station. On one occasion I saw a man with a radar speed gun checking train speeds, freight only as the passengers reversed even then. Never seen it since and no doubt is carried out much more automatically nowadays.

It’s still done.

 

[800301]

I hope that following the introduction of more ERTMS fitted lines there is some review to line speeds where signal sighting distance is the reason for a lower speed limit

 

[Bald Rick]

I hope that following the introduction of more ERTMS fitted lines there is some review to line speeds where signal sighting distance is the reason for a lower speed limit

’signalling’ ceases to be a constraint on line speeds with decent cab signalling. Sighting, spacing, approach control, etc etc all go.

 

[John Smith 19]

Technically possible doesn't make it a good idea - there are rapidly growing aerodynamic issues going faster than we are with not very aerodynamic loads ( like boxes made of flat sides with gaps between them, for instance ), and the energy use scales rapidly too. If you're not using diesel you can at least theoretically recover a lot of the energy put into increased initial acceleration, if not the later drag.

Which is another argument to go electric, especially if the CILT's proposal to electrify as little as 100 miles of single track would raise the amount of freight that could benefit from electrification substantially.

Better acceleration & not having to leave trains looped for hours because they can't get up to linespeed fast enough to not use an extra path would do even more to increase average speed than going to 90mph...

I mention 90mph for freight simply because it doesn't seem to have been seriously reviewed since the late 1960's. Caboose braked, unsprung freight trains simply don't exist on the UK network, and haven't since the mid 80's at the very latest.

As a passenger I want faster journey times. The presumption is that trains are too slow and only new trains IE High Speed rail can deliver this but IMHO there is a lot that could be done, but it's so difficult to identify issues that people don't do it.

 

[John Smith 19]

Better speeds at the pointwork at the ends of loops would help.

That sounds like a plan that should be applied at the entry and exit of all loops.

 

[John Smith 19]

’signalling’ ceases to be a constraint on line speeds with decent cab signalling. Sighting, spacing, approach control, etc etc all go.

Yes. A lot of problems seem to disappear once the lights are inside the cab.

But my impression is that it's so damm expensive. Getting rid of all those signals out in the field should save a significant amount of money. But you're never going to get rid of the need for points, and the need for something to control them.

 

[The Planner]

That sounds like a plan that should be applied at the entry and exit of all loops.

You need to sort the funding of that first, asset managers are funded to renew, not enhance the vast manority of the time. Exit speeds are far more important than entry, on the basis you are approaching a red at the end of the loop so unlikely to be hitting the entry speed anyway.

 

[CEN60]

Another thing that needs to be considered - increasing speed as all well and good - but in a lot of cases it just gets you to a "bottleneck" quicker.

There is no point in getting to the outside of a large terminus station throat if all it means is you sit outside the station for longer because of capacity constraints. The "whole system" needs looked at. I was once asked how can we get between A & B faster (names withheld to protect the guilty / innocent) - to which the initial replay was "easy - don't stop at the stations - that saves loads of time" - as I said the whole "system & interaction" needs to be assessed - not just speed.

It is actually possible to reduce the Sectional Appendix Linespeed but improve the journey time - Track reconfiguration at Elgin is a case in point - Speed was dropped, but because the manual token exchange was removed the actual journey time was decreased as there was no longer a need for the driver to slow down and exchange a token! (Hope that makes sense)

 

[Ken H]

Another thing that needs considered - increasing speed as all well and good - but in a lot of cases it just gets you to a "bottleneck" quicker. There is no point in getting the outside of a large terminus station throat if all it means is you sit outside the station for longer because of capacity constraints. The "whole system" needs looked at. I was once asked how can we get between A & B faster (names witheld to protect the guilty / innocent) - to which the initial replay was "easy - don't stop at the stations - that saves loads of time" - as I said the whole "system & interaction" needs assessed - not just speed. It is actually possible to reduce the Sectional Appendix Linespeed but improve the journey time - Track Reconfig at Elgin is a case in point - Speed was dropped, but because the manual token exchange was removed the actual journey time was decreased as there was no longer a need for the driver to slow down and exchange a token! (Hope that makes sense)

Quite. Often you can cut journey times without going faster. Grade separated junctions are more free flowing so you can cut recovery time, for instance.
But getting to a speed and then maintaining a constant speed has an energy consumption benefit compared to frequent speed changes.