Future of SP differentials?

[edwin_m]

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?

I suspect that's largely a historic issue. With the disappearance of older MUs, I expect nearly all that remain have weight and dynamic behaviour similar to a Sprinter (exception being the 185s, but I don't think they can use MU speeds either). So they could probably be qualified to use SP differentials if there had been any reason to. Any conversion of SP to MU would have to assess all classes that were permitted to use that route to confirm they met the criteria. If some didn't then there would be a choice of modifying whatever bits of infrastructure were vulnerable to the differences, issuing a special instruction preventing that class using the MU speeds on a particular section - or most likely leaving the SP speeds in place until something else turned up...

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.

There's some logic to that, but currently I believe the differential speeds are always higher than the basic speed and I think there would be a safety concern about starting to make them lower. Also there may be speeds that MUs can use but intercity trains (which will similarly nearly all be allowed HST differentials) can't.

 

[hexagon789]

So the sectional appendix downloads on the Network Rail website, even though they are dated Feb 2021, are out of date in some respects and both 755s and 195s are fully-authorised to run at SP speeds.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?

If you go through all the various sectional appendices you'll find plenty of omissions from the publically available online copies even with the dates that have.

I would imagine it's permanent otherwise many timetables would be up the spout if they were removed!

I suspect that's largely a historic issue. With the disappearance of older MUs, I expect nearly all that remain have weight and dynamic behaviour similar to a Sprinter (exception being the 185s, but I don't think they can use MU speeds either). So they could probably be qualified to use SP differentials if there had been any reason to. Any conversion of SP to MU would have to assess all classes that were permitted to use that route to confirm they met the criteria. If some didn't then there would be a choice of modifying whatever bits of infrastructure were vulnerable to the differences, issuing a special instruction preventing that class using the MU speeds on a particular section - or most likely leaving the SP speeds in place until something else turned up...

I was thinking of HSTs which can use DMU and MU but not SP speeds. The power car axle loads might be too high for using SP speeds compared to a DMU for instance.

 

[edwin_m]

If you go through all the various sectional appendices you'll find plenty of omissions from the publically available online copies even with the dates that have.

I would imagine it's permanent otherwise many timetables would be up the spout if they were removed!


I was thinking of HSTs which can use DMU and MU but not SP speeds. The power car axle loads might be too high for using SP speeds compared to a DMU for instance.

Indeed, as per the bit of my post that you didn't quote. Which I think means that on quite a lot of routes there will be significant numbers of trains that can't take the MU differentials, making it less likely these could be treated as the "default" speed. Much more so if 80x can't be cleared for SP speeds either.

 

[hexagon789]

Indeed, as per the bit of my post that you didn't quote. Which I think means that on quite a lot of routes there will be significant numbers of trains that can't take the MU differentials, making it less likely these could be treated as the "default" speed. Much more so if 80x can't be cleared for SP speeds either.

Apologies, I see you did address my point re HSTs. I confess I only read the section replying to my previous post.

Going back to the HST issue though, either work is done to allow all MU passed trains to run on routes where the prevailing differential is SP or the speeds are downgraded if MU becomes the 'default'. Alternatively SP remains for those lines which cannot be upgraded.

As to 80x, they must be a similar weight to 221s if not even heavier but presumably not as heavy as 185s as afaik 80x are passed for MU and DMU speeds as per HSTs.

All in all it looks like a bit of a mess to be worked out somehow