Why is one longish stretch of straight track different speeds on different lines?

[cambsy]

I have watched drivers eye views and cab rides, and have seen multiple times. Where a longish stretch of straight track is different speeds on different lines. So this got me wandering what affects the different speeds allowed? I know various things affect line speeds, so what generally affects a longish stretch of straight track line speed? And how easy is it and whats the cost of increasing line speed?.

 

[43066]

I have watched drivers eye views and cab rides, and have seen multiple times. Where a longish stretch of straight track is different speeds on different lines. So this got me wandering what affects the different speeds allowed? I know various things affect line speeds, so what generally affects a longish stretch of straight track line speed? And how easy is it and whats the cost of increasing line speed?.

Signal spacing, also location of refuges. Various factors.

 

[norbitonflyer]

Signal spacing possibly, but more often physical aspects of the track - fast and slow lines maintained to different standards (not necessarily better, just different: freight has heavier loads but lower kinetic forces). Kinetic envelope or aerodynamic effects of bridges, tunnels, lineside structures, or even strength of underbridges if the different tracks are supported by separate structures. Different braking curves for the types of train typically using them.

 

[MerlinRail 804]

This immediately makes me think of the section between Wycombe and Risborough on the Chiltern Mainline. Not talking about where it splits in two at the Saunderton Summit, but on the rest of that section, where the up linespeed is 100, the down linespeed (which is on an uphill) is only 85. The signal spacing seems to be the same and everything. Is it something to do with none of the trains being able to accelerate fast enough up the hill to get to 100?

 

[norbitonflyer]

There are places where the uphill speed limit is higher than downhill, because of the effect of gravity on stopping distances

 

[edwin_m]

One implied but not directly mentioned above, is if a four-track railway has four-aspect signals on the fast lines and three-aspect on the slows. The signals have to be alongside each other to avoid misreading, so the braking distance for the slow lines is only half that for the fast lines. This is perhaps more of a consequence than a reason for different speeds, because if the same speed had been necessary and possible then four-aspect would have been used on both sets of lines.

Another factor may be where the slow lines dogleg out to make room for an island platform but the fast lines remain straight. The curvature of the dogleg may be tight enough to impose a speed restriction.

 

[jfollows]

One implied but not directly mentioned above, is if a four-track railway has four-aspect signals on the fast lines and three-aspect on the slows. The signals have to be alongside each other to avoid misreading, so the braking distance for the slow lines is only half that for the fast lines. This is perhaps more of a consequence than a reason for different speeds, because if the same speed had been necessary and possible then four-aspect would have been used on both sets of lines.

King’s Cross to Hitchin springs to mind - now that it’s being resignalled with some kind of ETCS this may also have the benefit of increasing the speed limits on the slow lines.

 

[MerlinRail 804]

There are places where the uphill speed limit is higher than downhill, because of the effect of gravity on stopping distances

Not the case between West Wycombe and Saunderton. The uphill down line is 100 and the downhill up line is 85. I think most trains never reach that speed because of the climb, but I think the 68s might

 

[whoosh]

Sight lines from foot crossings affects linespeed. Signal sighting, not just spacing - so overbridges could be a factor on straight track.

 

[norbitonflyer]

Not the case between West Wycombe and Saunderton. The uphill down line is 100 and the downhill up line is 85. I think most trains never reach that speed because of the climb, but I think the 68s might

Then it is the case - uphill is faster than downhill

 

[MerlinRail 804]

Then it is the case - uphill is faster than downhill

Sorry, just realised my stupidity! It’s the other way round - the downhill up line is 100 and the uphill down line is 85

 

[Annetts key]

Um, as far as I am aware, the line speed is determined for each line separately depending on all the normal criteria.

On a two track railway, it's not that unusual for there to be a difference in the line speed between the two lines. The difference may be small or surprisingly large.

And if they are bidirectional lines, the speed for reversible working may be different to the normal direction speed.

 

[MatthewHutton]

This immediately makes me think of the section between Wycombe and Risborough on the Chiltern Mainline. Not talking about where it splits in two at the Saunderton Summit, but on the rest of that section, where the up linespeed is 100, the down linespeed (which is on an uphill) is only 85. The signal spacing seems to be the same and everything. Is it something to do with none of the trains being able to accelerate fast enough up the hill to get to 100?

The ridgeway crosses one of the lines on a level crossing. Presumably that is the 85mph one?

Possibly they didn’t think it was worth it if you have to slow down for that?

 

[DM352]

Oxted line - is 85 from Hurst Green to Lingfield but 70 the other direction.
Used to be similar Woldingham to Sanderstead with 85 but now both directions 70 as most electric trains stop all stations in the peak and guess cheaper at marginal lower speeds.

 

[Harpo]

a four-track railway has four-aspect signals on the fast lines and three-aspect on the slows. The signals have to be alongside each other to avoid misreading,

It hasn’t always been a consideration and (like many things!) it was left to drivers’ route knowledge in the past.

The down main approach to Newport was one example where on a left hand curve some down relief signals appeared (incorrectly) to be on the right of the down main’s then changed back to their correct side as you got nearer.

 

[Tractor37]

How about Baildon in West Yorkshire. On a single line - no other features apart from 2 tunnels. Going up the hill away from Baildon it’s 50mph. Yet coming down the hill towards Baildon it’s 60mph!

 

[Railwaysceptic]

I have watched drivers eye views and cab rides, and have seen multiple times. Where a longish stretch of straight track is different speeds on different lines. So this got me wandering what affects the different speeds allowed? I know various things affect line speeds, so what generally affects a longish stretch of straight track line speed? And how easy is it and whats the cost of increasing line speed?

In my strictly non-professional opinion, the biggest reason for different speeds over similar stretches of straight track is the attitude - and determination - of the people with responsibility for the line in question. When it's a major main line, the line speed is thought to be crucially important and large sums are spent to enable the fastest speeds possible. The East Coast and West Coast Main lines are prominent examples of this. On long stretches of dead straight track on lines regarded as less important, the line speed is irritatingly slow. Examples of this are between Brough and the outskirts of Selby and between Seamer and Malton. This difference in attitude is apparent not only on straight stretches of track. It's even more evident when the route has speed restricting curves. Witness the speeds permitted on the ECML between Darlington and Newcastle compared with the speed allowed over similarly sinuous track on secondary routes.

 

[Harpo]

the biggest reason for different speeds over similar stretches of straight track is the attitude - and determination - of the people with responsibility for the line in question

Or to give its proper name, the business case.

 

[PLY2AYS]

Not the case between West Wycombe and Saunderton. The uphill down line is 100 and the downhill up line is 85. I think most trains never reach that speed because of the climb, but I think the 68s might

Does it need to be any faster though?

Even if you’re on a fast, you still have to slow to 60 for Wycombe… it’ll be a struggle to get over 85 on most services.

Until Chiltern (hopefully) gets new units of course…

 

[LNW-GW Joint]

The sole example of EPS line speeds north of Carstairs on the WCML, for 2 miles through Shieldmuir, only applies to the Down line (signed PS90/EPS105).
The Up line has just PS95.

 

[hexagon789]

The sole example of EPS line speeds north of Carstairs on the WCML, for 2 miles through Shieldmuir, only applies to the Down line (signed PS90/EPS105).
The Up line has just PS95.

It's actually also HST105, the latter is the reason an EPS105 was agreed to be permitted there.

The HST105 dates from when IC225s and some XC HSTs went that way.

 

[norbitonflyer]

The ridgeway crosses one of the lines on a level crossing. Presumably that is the 85mph one?

It is. There are actually two pedestrian crossings on that stretch. The (downhill) up line is in a tunnel where the Ridgeway crosses it

Location Map.

Location map of 480124,201016.

www.streetmap.co.uk

 

[Bald Rick]

In my strictly non-professional opinion, the biggest reason for different speeds over similar stretches of straight track is the attitude - and determination - of the people with responsibility for the line in question. When it's a major main line, the line speed is thought to be crucially important and large sums are spent to enable the fastest speeds possible. The East Coast and West Coast Main lines are prominent examples of this. On long stretches of dead straight track on lines regarded as less important, the line speed is irritatingly slow. Examples of this are between Brough and the outskirts of Selby and between Seamer and Malton. This difference in attitude is apparent not only on straight stretches of track. It's even more evident when the route has speed restricting curves. Witness the speeds permitted on the ECML between Darlington and Newcastle compared with the speed allowed over similarly sinuous track on secondary routes.

As someone responsible for setting and revising linespeeds in the past (and maintaining / operating them) I can confirm that it is never due to the attitude of the people with responsibility for the line in question.

Linespeed profiles are set for technical reasons, and technical reasons only. And there are lots of technical reasons, as I have mentioned in many posts on these pages over the past decade and more. Alignment is just one of them.

There may be a business reason for improving journey times, and linespeed profiles may subsequently be revised. But the reason for any specific linespeed applied in any particular location is always technical.

 

[Tilting007]

Or to give its proper name, the business case.

Exactly this.
If it offers no benefit there is no point.
Quicker journeys, timetable resilience are all well but then there is plenty of cost for the feasibility studies alone. If any signalling changes are needed or power upgrades it quickly becomes expensive, even if at face value it looks easy.

Plus depends on drivability too.

 

[Railwaysceptic]

As someone responsible for setting and revising linespeeds in the past (and maintaining / operating them) I can confirm that it is never due to the attitude of the people with responsibility for the line in question.

Linespeed profiles are set for technical reasons, and technical reasons only. And there are lots of technical reasons, as I have mentioned in many posts on these pages over the past decade and more. Alignment is just one of them.

There may be a business reason for improving journey times, and linespeed profiles may subsequently be revised. But the reason for any specific linespeed applied in any particular location is always technical.

I was not suggesting that those responsible for a route set the line speed regardless of safety and technical considerations. I thought my post made it clear that I was referring to decisions made or not made to enable lines speeds to be raised.

 

[Kilopylae]

In my strictly non-professional opinion, the biggest reason for different speeds over similar stretches of straight track is the attitude - and determination - of the people with responsibility for the line in question. When it's a major main line, the line speed is thought to be crucially important and large sums are spent to enable the fastest speeds possible. The East Coast and West Coast Main lines are prominent examples of this. On long stretches of dead straight track on lines regarded as less important, the line speed is irritatingly slow. Examples of this are between Brough and the outskirts of Selby and between Seamer and Malton. This difference in attitude is apparent not only on straight stretches of track. It's even more evident when the route has speed restricting curves. Witness the speeds permitted on the ECML between Darlington and Newcastle compared with the speed allowed over similarly sinuous track on secondary routes.

To some extent it's just not that surprising that more investment is available to get mainlines up to snuff to run at higher speeds compared with local services.

 

[Harpo]

I was referring to decisions made or not made to enable lines speeds to be raised.

Which came across as suggesting attitudinal failings were a cause. NR’s strategic route plans are available on line for an in-depth explanation of attitudes.

 

[D6130]

Back in the day when I was involved in train planning (late 1970s/early 1980s), there were five track maintenance categories for BR lines:

A - maximum speed 90 or above
B - maximum speed 75-85
C - maximum speed 55-70
D - maximum speed 30-50
E - maximum speed less than 30

The maintenance budget for each category of line increased incrementally according to the speed category. Not sure whether this is still the case. @Bald Rick will be able to tell us.

If you have a steeply-graded section of otherwise well-aligned main line, it makes sense to have a lower speed limit on the uphill line - if trains are unlikely to be able to reach a higher speed - in order to save money on maintenance. As well as the High Wycombe-Saunderton section already quoted, another example that springs to mind is Huddersfield-Marsden, which is 70 on the Up and 85 on the Down.

 

[Bald Rick]

I thought my post made it clear that I was referring to decisions made or not made to enable lines speeds to be raised.

That’s not about attitude of those responsible for the lines in question. It’s about the economics of the lines in question. I have raised linespeeds on some lines, and not on others.

The maintenance budget for each category of line increased incrementally according to the speed category. Not sure whether this is still the case. @Bald Rick will be able to tell us

It’s similar, but now related to linespeed and annual gross tonnage on the line. Strictly speaking there isn’t a direct link to budget, as the track category drives inspection levels, not the maintenance required. For example a line with 100mph linespeed and 5m tonnes a year is Cat2, as is one at 60moh and 30m tonnes a year. They both have the same level of inspection, but the latter will have much higher maintenance intervention (and thus budget). Also there is variation depending on the type of track, and what it sits on. Heavily trafficked lines on the fens need a lot more intervention to similar lines built on rock.

 

[Railperf]

There are places where the uphill speed limit is higher than downhill, because of the effect of gravity on stopping distances

On the Highland main line the appear to be stretches with quite lower limits uphill - presumably because Class 170s and the older longer 2+8, 2+9 HSTs could not reach higher speeds. The 4 carv HST's would easily go faster but so far the limits were never raised to take advantage of this.
Similarly the MML limit northbound Bedford to Sharnbrook is limited to 110mph where downhill it is 125mph.