Future of SP differentials?

Status
Not open for further replies.

Rhydgaled

Established Member
Joined
25 Nov 2010
Messages
3,937
It is often noted in these forums that class XXX is not suitable for cascade to route YYYY to ZZZZ because class XXX would not be permitted to run at the full permissable speed to the route due to the full speed being an SP (Sprinter, although Turbostars are permitted to use them) differential. Given that they are expected to replace Sprinters and/or Turbostars, I had expected the new CAF Civity (class 195/196/197) and Stadler FLIRT (class 755) units to be designed to be compliant with 'Sprinter' specifications and permitted to run at SP linespeeds. However, the latest PDF downloads of the Sectional Appendix from network Rail do not list the class 755 or 195, so presumably they are limited to loco-haul and MU limits.

Are we likely to see any new stock that is able to run at SP speeds or is the regional network likely to see a slowdown as first Sprinters and then Turbostars are withdrawn?
 
Sponsor Post - registered members do not see these adverts; click here to register, or click here to log in
R

RailUK Forums

Shwam3

Member
Joined
13 Jun 2016
Messages
107
Location
Norwich
755s are authorised to run at SP and MU differential speeds in their Summary of Compatibility document (not published publicly).
 

hexagon789

Veteran Member
Joined
2 Sep 2016
Messages
12,002
Location
Glasgow
It is often noted in these forums that class XXX is not suitable for cascade to route YYYY to ZZZZ because class XXX would not be permitted to run at the full permissable speed to the route due to the full speed being an SP (Sprinter, although Turbostars are permitted to use them) differential. Given that they are expected to replace Sprinters and/or Turbostars, I had expected the new CAF Civity (class 195/196/197) and Stadler FLIRT (class 755) units to be designed to be compliant with 'Sprinter' specifications and permitted to run at SP linespeeds. However, the latest PDF downloads of the Sectional Appendix from network Rail do not list the class 755 or 195, so presumably they are limited to loco-haul and MU limits.

Are we likely to see any new stock that is able to run at SP speeds or is the regional network likely to see a slowdown as first Sprinters and then Turbostars are withdrawn?
755s can and do use SP speeds, though there was concern when they were new that they wouldn't be able to.

The 195s may be able to but the SA hasn't been updated. They can be very slow to update it.
 

Nymanic

Member
Joined
6 Jan 2014
Messages
143
Location
Manchester
Since the Class 195 cars weigh less than respective Class 170 vehicles (although they're not as light as Class 172s), I'd be surprised if they couldn't run to SP differentials - sadly I can't confirm either way.

But given the ongoing yaw damper issue - if the design of the inside frame bogie is found to be a contributing factor - might we start to see a return to more conventional bogie designs on future stock?

If that happens, and those weight savings are lost, will it no longer be possible to make trains light enough to run to SP speeds?

It's a rock and a hard place - at one end, lightweight bogies that compromise comfort and might contribute to safety issues down the line; at the other, conventional bogie designs that result in lower speeds and/or higher track access charges...
 

Domh245

Established Member
Joined
6 Apr 2013
Messages
8,067
Location
nowhere
But given the ongoing yaw damper issue - if the design of the inside frame bogie is found to be a contributing factor - might we start to see a return to more conventional bogie designs on future stock?

If that happens, and those weight savings are lost, will it no longer be possible to make trains light enough to run to SP speeds?

Given that Bombardier have been running inside frame bogies around since the voyagers without issue*, and Siemens have similarly been running inside frame bogies on the 700s for 5 years now - I don't think it's an inherent issue with lightweight bogies so much as the implementation on the civities!

*There was an issue with a 222 where it broke an axle because of a seized bearing, but other than that
 

Llama

Established Member
Joined
29 Apr 2014
Messages
1,909
We're still waiting for 331s to appear in the sectional appendix table D at all, nearly two years after they entered revenue service.

And yes, 195s can run at SP, MU, DMU and HST speeds. Although the only place that's documented for drivers to reference is in the training course.
 

hexagon789

Veteran Member
Joined
2 Sep 2016
Messages
12,002
Location
Glasgow
We're still waiting for 331s to appear in the sectional appendix table D at all, nearly two years after they entered revenue service.

And yes, 195s can run at SP, MU, DMU and HST speeds. Although the only place that's documented for drivers to reference is in the training course.
Presumably the 331s can use EMU/MU?
 

D6130

Established Member
Joined
12 Jan 2021
Messages
1,457
Location
West Yorkshire/Tuscany
The SP speed restrictions on the York-Scarborough line have been a complete waste of time since the 185s replaced the 158s on that route many years ago, although I suppose there may be the occasional Northern empty stock or crew training run that could take advantage of them. However, if and when the proposed Northern York-Scarborough service eventually commences, they will come back into their own.
 

talltim

Established Member
Joined
17 Jan 2010
Messages
2,426
It’s a higher speed limit on a section of line, for lightweight DMUs.
 

HSTEd

Veteran Member
Joined
14 Jul 2011
Messages
13,803
Could someone explain what an SP differential is, for the uninitiated? :lol:
An SP differential speed is a higher speed limit for certain classes of train.

It was originally introduced during "Sprinterisation", when the lower axle loads of the new fleet of lightweight multiple units made higher speeds economic in terms of track damage etc.

(When Sprinters were replacing all sorts of things, including loco hauled trains)
 

hexagon789

Veteran Member
Joined
2 Sep 2016
Messages
12,002
Location
Glasgow
An SP differential speed is a higher speed limit for certain classes of train.

It was originally introduced during "Sprinterisation", when the lower axle loads of the new fleet of lightweight multiple units made higher speeds economic in terms of track damage etc.

(When Sprinters were replacing all sorts of things, including loco hauled trains)
Is it just axle load? I thought the sharper braking as well, at least some accounts suggest that it's the axle load AND better brakes - I've never really been sure if that's correct
 

edwin_m

Veteran Member
Joined
21 Apr 2013
Messages
21,755
Location
Nottingham
Is it just axle load? I thought the sharper braking as well, at least some accounts suggest that it's the axle load AND better brakes - I've never really been sure if that's correct
The 150s and 156s can use SP differentials and just have traditional tread brakes, so there can't be any better braking requirement up to 75mph. I think SP differentials may require 9%g brakes only if they are above 75mph, only 158s being able to use those at the time they were introduced.
 

ac6000cw

Established Member
Joined
10 May 2014
Messages
2,238
Location
Cambridge, UK
Is it just axle load? I thought the sharper braking as well, at least some accounts suggest that it's the axle load AND better brakes - I've never really been sure if that's correct
That was certainly the case with the HST differentials - allowing 125 mph on lines signalled for 100 mph loco-hauled trains. I think the SP differential was primarily introduced to allow 158/159s to run at 90 mph on otherwise 75 mph lines (as they have lower track forces and disc brakes). The earlier Sprinter family DMUs are only 75 mph capable anyway, but I guess SP might allow those to run at that on otherwise lower speed lines?
 
Last edited:

hexagon789

Veteran Member
Joined
2 Sep 2016
Messages
12,002
Location
Glasgow
The 150s and 156s can use SP differentials and just have traditional tread brakes, so there can't be any better braking requirement up to 75mph. I think SP differentials may require 9%g brakes only if they are above 75mph, only 158s being able to use those at the time they were introduced.
So for limits over 90 the better braking is a requirement, but for 75 it isn't? So a first generation DMU could theoretically be passed for SP differentials?


The earlier Sprinter family DMUs are only 75 mph capable anyway, but I guess SP might allow those to run at that on otherwise lower speed lines?
I was thinking the electric controlled brakes with a slightly higher 7%g full service deceleration against the quoted 6%g for traditional tread braked trains might be enough to allow a higher speed in addition to the axle loading.
 

edwin_m

Veteran Member
Joined
21 Apr 2013
Messages
21,755
Location
Nottingham
So for limits over 90 the better braking is a requirement, but for 75 it isn't? So a first generation DMU could theoretically be passed for SP differentials?



I was thinking the electric controlled brakes with a slightly higher 7%g full service deceleration against the quoted 6%g for traditional tread braked trains might be enough to allow a higher speed in addition to the axle loading.
The standard for braking distances only gives a "standard" table for all trains, a passenger only table and one for 9%g brakes, so I don't think 150s get any benefit in that respect. This suggests first generation DMUs might qualify on braking and axle load, however their ride was much poorer so they might cause more track damage. In any case, by the time SP differentials came along first generation DMUs weren't long for this world, so nobody would have spent much time trying to get them approved.
 

hexagon789

Veteran Member
Joined
2 Sep 2016
Messages
12,002
Location
Glasgow
In any case, by the time SP differentials came along first generation DMUs weren't long for this world, so nobody would have spent much time trying to get them approved.
Yeah that seems fair enough

Northallerton - Thirsk has stretches of 80/90SP on the slows
Introduced specifically for the 158s to allow them to run at maximum speed on the slow lines
 

hexagon789

Veteran Member
Joined
2 Sep 2016
Messages
12,002
Location
Glasgow
Thanks for that. Since the 185s replaced the 158s I don't think there is anything regularly using that section that would qualify for the SP speeds.
I don't think there is but presumably there is no higher maintenance requirement though otherwise they might have been removed on cost grounds and downgraded to a plain '80'?
 

Class 170101

Established Member
Joined
1 Mar 2014
Messages
6,908
755s are authorised to run at SP and MU differential speeds in their Summary of Compatibility document (not published publicly).

755s can and do use SP speeds, though there was concern when they were new that they wouldn't be able to.

I seem to recall there was a proposal by NR to change the SP boards to MU speed boards whether that happened or not who knows.
 

Shwam3

Member
Joined
13 Jun 2016
Messages
107
Location
Norwich
I seem to recall there was a proposal by NR to change the SP boards to MU speed boards whether that happened or not who knows.

That project is still underway though I don't believe any on-network changes have actually happened as yet.
 

hexagon789

Veteran Member
Joined
2 Sep 2016
Messages
12,002
Location
Glasgow
I seem to recall there was a proposal by NR to change the SP boards to MU speed boards whether that happened or not who knows.
Be interesting to see how that develops - plenty of classes which can use MU speeds but not SP, how will that be accommodated? Lower speeds?
 

ac6000cw

Established Member
Joined
10 May 2014
Messages
2,238
Location
Cambridge, UK
I can't help thinking that now the 'standard' passenger train is an MU pretty much everywhere on the network, it might be sensible to turn things on their head and make the 'MU' or SP speeds the standard linespeed, with speed restrictions/reductions for loco-hauled trains i.e. freight and a relative handful of passenger trains as required.
 

Rhydgaled

Established Member
Joined
25 Nov 2010
Messages
3,937
755s are authorised to run at SP and MU differential speeds in their Summary of Compatibility document (not published publicly).

755s can and do use SP speeds, though there was concern when they were new that they wouldn't be able to.

The 195s may be able to but the SA hasn't been updated. They can be very slow to update it.

195s can run at SP differentials
So the sectional appendix downloads on the Network Rail website, even though they are dated Feb 2021, are out of date in some respects and both 755s and 195s are fully-authorised to run at SP speeds. Glad to hear it; are these permanent authorisations?
 
Status
Not open for further replies.

Top