GWML Electification

[Geoff Endacott]

Yes.

 

Geoff Endacott

[DY444]

9 hours ago, rodent279 said:

Just so I am clear about what is being discussed, are these the St Andrews Crosses, pictured to the left of the Voyager in this photo?

 

 

 

Yes

[rodent279]

On 10/04/2020 at 22:16, rodent279 said:

Just so I am clear about what is being discussed, are these the St Andrews Crosses, pictured to the left of the Voyager in this photo?

 

 

 

 

All gone in almost the same shot, a year later in July 2018.

 

Edited September 3, 2022 by rodent279

[talisman56]

The current separation point between Platforms 3 and 4 is a bit further down the platform, behind the photographer. The current length of Platform 4 is just longer than a 2+4HST, judging by the distance I had to walk to get to the train the last time I had to catch a train from that platform.

Edited April 13, 2020 by talisman56
digital dyslexia

[rodent279]

On 10/04/2020 at 22:16, rodent279 said:

Just so I am clear about what is being discussed, are these the St Andrews Crosses, pictured to the left of the Voyager in this photo?

 

 

Is the red thing hanging down from the canopy, just in front of the camera, the rear of a St Andrew's cross?

Edited April 14, 2020 by rodent279

[DY444]

11 hours ago, rodent279 said:

Is the red thing hanging down from the cannot, just in front of the canopy, the rear of a St Andrew's cross?

 

No.  They were double sided and there was only one on the platforms which had them fitted. 

 

I'm guessing now but the original crosses were non-illuminated and these were replaced in the late 80s by illuminated versions.  The fitting you refer to *might* be where the original non-illuminated crosses were mounted.

Edited April 14, 2020 by DY444

[caradoc]

16 hours ago, talisman56 said:

The current separation point between Platforms 3 and 4 is a bit further down the platform, behind the photographer. The current length of Platform 4 is just longer than a 2+4HST, judging by the distance I had to walk to get to the train the last time I had to catch a train from that platform.

 

Last summer I caught a westbound 2+4 HST from platform 4, travelling to Weston-Super-Mare; By the time I got to the train I was already halfway there !

[Platform 1]

Looks like Steventon bridge reprieve is official: https://www.networkrailmediacentre.co.uk/news/bridge-in-oxfordshire-to-remain-in-place-following-state-of-the-art-testing

 

[The Stationmaster]

13 hours ago, Platform 1 said:

Looks like Steventon bridge reprieve is official: https://www.networkrailmediacentre.co.uk/news/bridge-in-oxfordshire-to-remain-in-place-following-state-of-the-art-testing

 

Until it requires major repair work presumably?     It's already a bit like Trigger's broom.  BTW I wonder if the parapets have been raised - ah, answer my own question as it has been fitted with some fancy metal grills, shame they haven't been used on other bridges as they look pretty neat.

[uax6]

That's the first time I've seen a picture of the bridge, and I can see nothing worth keeping about it....

 

Andy g

[jim.snowdon]

10 hours ago, uax6 said:

That's the first time I've seen a picture of the bridge, and I can see nothing worth keeping about it....

 

Andy g

Exactly. It's only significance was as a means for preventing the residents of Steventon from the inconvenience of rebuilding works. At the same time it has interesting to see what little effort appeared to have expended in exploring alternative solutions to the low/high wire problem created by the proximity of the bridge and the two level crossings.

 

Jim

[Trog]

I wonder how much it will cost over the years to slow and accelerate every electric express train going under it by 15MPH.

[jim.snowdon]

Provided the contact wire overlaps are in sensible places and the train's on board electronics can cope with the temporary power loss, the option was always there to simply drop the pans, coast through at the full line speed, and raise the pans again once clear of the crossings.

 

Jim

[jim.snowdon]

Provided the contact wire overlaps are in sensible places and the train's on board electronics can cope with the temporary power loss, the option was always there to simply drop the pans, coast through at the full line speed, and raise the pans again once clear of the crossings.

 

Jim

[rodent279]

3 hours ago, Trog said:

I wonder how much it will cost over the years to slow and accelerate every electric express train going under it by 15MPH.

Possibly not as much as you think, given that for some trains, it will fit in with braking for a stop at Didcot, and that IET's can brake using regenerative brakes, so feeding juice back into the network. Yes, there will be energy loss, but it's probably bearable.

Edited April 25, 2020 by rodent279

[The Stationmaster]

1 hour ago, rodent279 said:

Possibly not as much as you think, given that for some trains, it will fit in with braking for a stop at Didcot, and that IET's can brake using regenerative brakes, so feeding juice back into the network. Yes, there will be energy loss, but it's probably bearable.

It certainly wouldn't fit in with braking from 125 mph for a Didcot stop because it's bit over 3 miles from the west end of Didcot's platforms.  Thus the time cost for an up train stopping at Didcot will be exacerbated by dropping to 110mph for the bridge because the train inevitably won't accelerate back to 125mph before braking for Didcot.  So whatever the energy and brake wear cost there will also be a time cost - not much but still a cost.  One real example taken from Real Time Trains indicates the loss could be as much as 30 seconds although that might in part be accounted for by the way the offsets are arranged.

 

In the Down direction there will also be a time cost and a potential energy wastage cost because the train which has stopped at Ddcot will not have a smooth acceleration curve between Didcot and Wantage Road.  There will of course be an impact on all other IETs not calling at Didcot as they will have to brake for teh reduction in line soeed and then accelerate back up to full line speed.

 

Overall the 'solution' is really no more than a 'best possible' fairly pragmatic compromise forced by the fact that the bridge cannot be rebuilt, nor level crossings closed, for what are in reality 'political' reasons rather than practical engineering reasons.  If Stocks Lane Crossing could be closed that would give an extra 14 chains to ease the contact wire gradient (which might or might not make a difference to the maximum permissible speed?) but we don't know if that option was assessed to see if it would make a difference.

[talisman56]

I wonder how long before bits start dropping off the bridge due to bow-shock and vibration...

[The Stationmaster]

10 minutes ago, talisman56 said:

I wonder how long before bits start dropping off the bridge due to bow-shock and vibration...

As bits have been breaking on it for a long time it might not be far off.  However judging by the look of various bits of replacement brickwork (but not the side arch strengthening) I would suspect road traffic damage was more the cause rather than rail vibration.  and of course traffic loads on the road dropped considerably when the Steventon bypass was built although local traffic has seemingly increased considerably in recent years.

 

The concrete bracing in the Up side wing arch is typical of that put into a number of brick arch bridges on the GWML and is perhaps not related to road loadings as some of the bridges so strengthened are considerably quieter than was the case at Steventon suggesting it is more likely down to the type of structure rather than anything else. 

[St. Simon]

Hi,

 

For those that are interested, despite COVID, next Sunday afternoon should see electric operation through the Severn Tunnel.

 

This will mean that the GWML electrification scheme is finished*
 

*well, not ‘finished‘, but the current scope has been complete, for now..... 

 

Simon

[DY444]

On 25/04/2020 at 16:20, The Stationmaster said:

It certainly wouldn't fit in with braking from 125 mph for a Didcot stop because it's bit over 3 miles from the west end of Didcot's platforms.  Thus the time cost for an up train stopping at Didcot will be exacerbated by dropping to 110mph for the bridge because the train inevitably won't accelerate back to 125mph before braking for Didcot.  So whatever the energy and brake wear cost there will also be a time cost - not much but still a cost.  One real example taken from Real Time Trains indicates the loss could be as much as 30 seconds although that might in part be accounted for by the way the offsets are arranged.

 

In the Down direction there will also be a time cost and a potential energy wastage cost because the train which has stopped at Ddcot will not have a smooth acceleration curve between Didcot and Wantage Road.  There will of course be an impact on all other IETs not calling at Didcot as they will have to brake for teh reduction in line soeed and then accelerate back up to full line speed.

 

Overall the 'solution' is really no more than a 'best possible' fairly pragmatic compromise forced by the fact that the bridge cannot be rebuilt, nor level crossings closed, for what are in reality 'political' reasons rather than practical engineering reasons.  If Stocks Lane Crossing could be closed that would give an extra 14 chains to ease the contact wire gradient (which might or might not make a difference to the maximum permissible speed?) but we don't know if that option was assessed to see if it would make a difference.

 

I've heard it suggested that a compromise to avoid closure of the crossing is that a road vehicle height limit could be imposed as a way of reducing the contact wire height there and thus its gradient approaching the bridge.  Obviously there would have to be a robust structure of some sort each side to stop over height vehicles and it does sound like something that would fall foul of the H&S mafia but it is a theoretical option ...

Edited May 23, 2020 by DY444

[Titan]

On 25/04/2020 at 16:20, The Stationmaster said:

It certainly wouldn't fit in with braking from 125 mph for a Didcot stop because it's bit over 3 miles from the west end of Didcot's platforms.  Thus the time cost for an up train stopping at Didcot will be exacerbated by dropping to 110mph for the bridge because the train inevitably won't accelerate back to 125mph before braking for Didcot.  So whatever the energy and brake wear cost there will also be a time cost - not much but still a cost.  One real example taken from Real Time Trains indicates the loss could be as much as 30 seconds although that might in part be accounted for by the way the offsets are arranged.

 

In the Down direction there will also be a time cost and a potential energy wastage cost because the train which has stopped at Ddcot will not have a smooth acceleration curve between Didcot and Wantage Road.  There will of course be an impact on all other IETs not calling at Didcot as they will have to brake for teh reduction in line soeed and then accelerate back up to full line speed.

 

Overall the 'solution' is really no more than a 'best possible' fairly pragmatic compromise forced by the fact that the bridge cannot be rebuilt, nor level crossings closed, for what are in reality 'political' reasons rather than practical engineering reasons.  If Stocks Lane Crossing could be closed that would give an extra 14 chains to ease the contact wire gradient (which might or might not make a difference to the maximum permissible speed?) but we don't know if that option was assessed to see if it would make a difference.

 

It is not the best possible solution, all that has been done is to run a simulation backed up by test trains on the OLE as installed to see how fast you can go before contact wire forces get excessive.  As the rules for OLE installation are somewhat conservative and simplified to aid design, it is no surprise that higher speeds than the rules suggest are possible without exceeding maximum forces.  However, if designed from first principles instead of by the book, with some minor adjustment to the OLE - basically adjusting wire heights at some structures and changing some droppers, not only could 125mph be achieved, but most likely with less forces then the existing system does at 115mph.  Of course it would not be consistent with the existing rules, but then again running at 115mph on what's there isn't either.  

Edited May 23, 2020 by Titan

[Joseph_Pestell]

On 25/04/2020 at 16:20, The Stationmaster said:

It certainly wouldn't fit in with braking from 125 mph for a Didcot stop because it's bit over 3 miles from the west end of Didcot's platforms.  Thus the time cost for an up train stopping at Didcot will be exacerbated by dropping to 110mph for the bridge because the train inevitably won't accelerate back to 125mph before braking for Didcot.  So whatever the energy and brake wear cost there will also be a time cost - not much but still a cost.  One real example taken from Real Time Trains indicates the loss could be as much as 30 seconds although that might in part be accounted for by the way the offsets are arranged.

 

In the Down direction there will also be a time cost and a potential energy wastage cost because the train which has stopped at Ddcot will not have a smooth acceleration curve between Didcot and Wantage Road.  There will of course be an impact on all other IETs not calling at Didcot as they will have to brake for teh reduction in line soeed and then accelerate back up to full line speed.

 

Overall the 'solution' is really no more than a 'best possible' fairly pragmatic compromise forced by the fact that the bridge cannot be rebuilt, nor level crossings closed, for what are in reality 'political' reasons rather than practical engineering reasons.  If Stocks Lane Crossing could be closed that would give an extra 14 chains to ease the contact wire gradient (which might or might not make a difference to the maximum permissible speed?) but we don't know if that option was assessed to see if it would make a difference.

 

I see that this subject has reared its head again!

 

What is it about this particular village that causes such difficulties? It seems able to enrol more objectors than the whole of the Chilterns can raise against HS2.

 

1) There is space to build a road to link the part of the village that is south of the crossings to the old A34 south of the bridge. That would benefit much of the village as it would remove HGVs going to/from the industrial estate.

2) There is space to build a new road and bridge a bit further east (or a temporary bridge while they rebuild the old one).

3) Footbridges can be put in for pedestrians. 

[rodent279]

1 hour ago, Joseph_Pestell said:

 

I see that this subject has reared its head again!

 

What is it about this particular village that causes such difficulties? It seems able to enrol more objectors than the whole of the Chilterns can raise against HS2.

 

1) There is space to build a road to link the part of the village that is south of the crossings to the old A34 south of the bridge. That would benefit much of the village as it would remove HGVs going to/from the industrial estate.

2) There is space to build a new road and bridge a bit further east (or a temporary bridge while they rebuild the old one).

3) Footbridges can be put in for pedestrians. 

I think it's a classic case of people with the right connections making the right noises. If I objected no one would take a blind bit of notice, but if the right person makes the correct complaints to the right people, they get noticed. 

[rodent279]

2 hours ago, Titan said:

 

It is not the best possible solution, all that has been done is to run a simulation backed up by test trains on the OLE as installed to see how fast you can go before contact wire forces get excessive.  As the rules for OLE installation are somewhat conservative and simplified to aid design, it is no surprise that higher speeds than the rules suggest are possible without exceeding maximum forces.  However, if designed from first principles instead of by the book, with some minor adjustment to the OLE - basically adjusting wire heights at some structures and changing some droppers, not only could 125mph be achieved, but most likely with less forces then the existing system does at 115mph.  Of course it would not be consistent with the existing rules, but then again running at 115mph on what's there isn't either.  

Does that mean stiffer contact wire for a short length on the approach to and from the bridge?

[Titan]

19 minutes ago, rodent279 said:

Does that mean stiffer contact wire for a short length on the approach to and from the bridge?

 

No. All at standard tension/stiffness.

Edited May 23, 2020 by Titan