Forth Bridge: how would you electrify it?

[HowardGWR]

I seem to recall that when it was first designated as a world heritage site the principle of future electrification was cleared with Unesco. I think any chosen method will be accepted provided NR demonstrates that all reasonable alternative methods have been considered and mitigations applied.

I don't know what the planning policies are in Scotland but the WHS designation is only a p.m. planning issue in England. It's more the other way around, as Dresden found out when its recently built road bridge caused the section of Elbe banks WHS designation to be removed from WHS status.

 

[LOL The Irony]

build a new bridge...................

CoughMoneyCough

 

[ainsworth74]

Is it really impossible to lower the tracks?

It's probably not impossible as the track doesn't appear to sit directly on the bridge deck but slightly above it but lowering the tracks to sit directly on the deck would probably only buy you a few centimetres or so. Whether those would be the crucial centimetres I don't know but I suspect they wouldn't be. Plus, presumably, the bridge was designed have the track over it in the way it does currently for some reason so that might also be an issue!

 

[DackandBlecker]

From memory, the Forth Bridge used to have it's own special rails, however in the '90s(?) it was changed so the bridge has standard rails.
I think that it sits on wooden beams that hold the rails in place.

 

[Cowley]

build a new bridge...................

CoughMoneyCough

Yep, and the money you’ll get back from weighing the metal in from this one should cover some of the cost.

I’ll get my coat...

 

[HSTEd]

There's been a few trespass incidents in recent times.

Forth Rail Bridge trespasser 28/01 - could more be done to improve security?

The fact that the incident is newsworthy probably tells us something!

Additionally the rail could be powered down whenever trains weren't crossing the bridge.

 

[furnessvale]

From memory, the Forth Bridge used to have it's own special rails, however in the '90s(?) it was changed so the bridge has standard rails.
I think that it sits on wooden beams that hold the rails in place.

Photos indicate longitudinal waybeams. Whether the support arrangements could be altered to lower the rail height is certainly worthy of investigation, and no doubt will be done, if it hasn't been done already.

 

[TwistedMentat]

If you're only using the battery function for one unelectrified section you don't want to have to change the batteries every five years, which means you need a normal sized battery pack in order to maintain a low (e.g. 30%) depth of discharge.

Depending on the cost of other options it seems plausible to me it would still be the cheaper option. And if you limit the power draw for acceleration as the top speed of the bridge is only 40mph according to upthread, then the battery capacity can be pretty limited. Couple it with some slow charging from the overhead and some good battery management hardware then it should work long term.

I'm just reminded that back in Auckland, NZ the new trains they're getting will be EMUs with battery storage for short off wires stuff. That should provide examples of how well the idea works.

 

[najaB]

Given that there are really very low risks associated with tresspassers on the bridge..... why is a third rail solution verboten here?

It's not that it's verboten in this case, just it would be a 1 mile long 3rd rail island with the next nearest section of 3rd rail being nearly 200 miles away. Doesn't strike me as a particularly practical solution.

 

[markindurham]

It's not that it's verboten in this case, just it would be a 1 mile long 3rd rail island with the next nearest section of 3rd rail being nearly 200 miles away. Doesn't strike me as a particularly practical solution.

Absolutely. Plus the cost of fitting 3rd rail gear to everything expected to cross the bridge, with all the potential issues of loading gauge, electrical switchgear to keep it isolated when not in use etc etc. It's a non-starter

 

[HSTEd]

Absolutely. Plus the cost of fitting 3rd rail gear to everything expected to cross the bridge, with all the potential issues of loading gauge, electrical switchgear to keep it isolated when not in use etc etc. It's a non-starter

Except dual voltage versions of all major EMU families on the market today already exist.
The same cannot be said for all the other bespoke solutions given in this thread.

The design work alone would swamp the costs of equipping the relevant EMU fleets with third rail shoes.

It's not that it's verboten in this case, just it would be a 1 mile long 3rd rail island with the next nearest section of 3rd rail being nearly 200 miles away. Doesn't strike me as a particularly practical solution.

And introducing a lower voltage AC standard used nowhere else in Britain is practical?

EDIT:
It is interesting that discontinuous AC electrification is often assumed as requiring batteries and the like, even though using third rail for difficult sections like this and tunnels would eliminate the downsides of batteries and a high power power supply is even available for the DC supply in the form of the AC traction supply!

 

[markindurham]

Except dual voltage versions of all major EMU families on the market today already exist.
The same cannot be said for all the other bespoke solutions given in this thread.

The design work alone would swamp the costs of equipping the relevant EMU fleets with third rail shoes.

Agreed - the costs involved for such a tiny length of track would be disproportional.

Yes, there are dual voltage EMU fleets - but we are talking retrofitting to stock not designed for it. In addition, in many places away from the 3rd rail, there may well be clearance issues

 

[HSTEd]

Agreed - the costs involved for such a tiny length of track would be disproportional.

Yes, there are dual voltage EMU fleets - but we are talking retrofitting to stock not designed for it. In addition, in many places away from the 3rd rail, there may well be clearance issues

Well the fleets that would operate electric services over the bridge probably have either not been built yet, or will be one of the current surplus EMU families like the 319s or 365s.
Both of which have had third rail shoes fitted at various times.

AIUI most new build units can also have retractable third rail shoes fitted now.

 

[DackandBlecker]

Well the fleets that would operate electric services over the bridge probably have either not been built yet, or will be one of the current surplus EMU families like the 319s or 365s.
Both of which have had third rail shoes fitted at various times.

AIUI most new build units can also have retractable third rail shoes fitted now.

Do the IEPs that have been already to Aberdeen have shoes?
I don't think they do.

Putting down a third rail is falling in to the realms of fantasy.

 

[Aictos]

British Rail had plans in the 80's to wire up to Aberdeen so they must have found a solution otherwise they wouldn't have proposed it.

I wonder though what the solution was....

 

[Mollman]

Do the IEPs that have been already to Aberdeen have shoes?
I don't think they do.

Putting down a third rail is falling in to the realms of fantasy.

TBF they have diesel engines anyway. It would be likely as pointed out elsewhere that whatever solution is used for the Forth Bridge would be used for the Tay Bridge too.

 

[DackandBlecker]

TBF they have diesel engines anyway.

And the 9 car all electric ones don't either, for what that matters too.

It would be likely as pointed out elsewhere that whatever solution is used for the Forth Bridge would be used for the Tay Bridge too.

Would be interesting to know what they had in mind.

 

[gsnedders]

And the 9 car all electric ones don't either, for what that matters too.

They have one, and that's probably good enough for the chance of getting stranded on the bridge. None of them stop at Dalmeny or North Queensferry, after all, so they don't have the standing start issue.

 

[HSTEd]

Do the IEPs that have been already to Aberdeen have shoes?
I don't think they do.

A handful of long distance trains (three isn't it?) powering up the diesel generators they are already fitted with to cross the bridge is not really an issue.

Putting down a third rail is falling in to the realms of fantasy.

The way things are going, not as much of a fantasy as a 25kV electrification scheme being approved any time soon.

And the 9 car all electric ones don't either, for what that matters too.

They do have a diesel engine, and even one of the MTU diesels will give it a high enough power to weight ratio to get the train moving if it stops on the bridge. It will still beat a stone train in the P:W ratio stakes.

 

[Highlandspring]

It's not that it's verboten in this case, just it would be a 1 mile long 3rd rail island with the next nearest section of 3rd rail being nearly 200 miles away.

The nearest section of conductor rail to the Forth Bridge is less than 50 miles as the crow flies.

 

[gsnedders]

The nearest section of conductor rail to the Forth Bridge is less than 50 miles as the crow flies.

Where? Or are you including the Glasgow Subway here?

 

[edwin_m]

Although the bridge might at first appear to be less at risk of having people trackside, I'm sure there is an attraction to walking across it illegally and posting the video on YouTube or whatever. Also the bridge is a high-maintenance structure compared to a normal bit of railway and much of it can probably only be accessed by walking trackside. So the likelihood of people being on or about the line may actually be above average.

#16 shows that the Forth Bridge rails sit in a sort of trough with a raised bit either side. I'm pretty sure this is incompatible with a third rail in the traditional position (not to mention the risk of short circuits with the whole thing being made of metal). An under-contact third rail would avoid this problem and is less frowned upon by ORR, but would require some kind of retractable upside-down shoe which would probably hit the first platform and become a lethal missle to waiting passengers if not retracted correctly.

 

[najaB]

Or are you including the Glasgow Subway here?

I suspect so, though seeing as that isn't in any way connected to Network Rail metals it really isn't relevant.

 

[NotATrainspott]

HSTEd is there any question where your answer isn't third rail electrification?

Third rail doesn't solve enough problems, and it creates new ones. There is the obvious concern about safety, especially as the bridge is a special structure where normal maintenance access arrangements do not apply. New third rail installations for metro systems come with access routes to the side which mean that maintenance staff and evacuated passengers have little reason to come into contact with the third rail regardless of the state of the system. I can't see it being possible to add a compliant access route on the bridge.

Also, third rail DC just means you swap one set of electrical compatibility issues for another. Even if you have the physical clearance for the third rail and the train collector shoes, you have to worry about how you prevent stray currents ending up in places they're not meant to be. London Underground had to work out third rail DC in a metallic environment and they came up with a four rail solution. If you would need to do something like this, you'd be going for a unique system again.

Batteries are the best solution. In the worst case scenario where there is precisely zero clearance, an EMU can drop its pantograph and have the same loading gauge as a DMU. The battery means you can have inclines, stations and signals in the dead section which would make coasting impossible. Where there's physical but not electrical clearance, you can have neutral wires or conductor bars to avoid the need to raise and lower the pantograph. There's no need to do any more infrastructure changes than is absolutely required. The work is all on the rolling stock side. All of these options, including third-rail, require some special rolling stock treatment. Batteries would be one thing that would be universally useful across the country's EMU fleet, so there's no need for ROSCOs to worry about assets which are only useful in one setting. The battery-equipped trains running from Edinburgh to Dundee could later end up used to extend EMU services just beyond the end of the wires elsewhere.

 

[AndrewE]

And two VCBs, two pantograph up/down controls. What happens when someone forgets to lower the wide pantograph? What's more likely to fail and cause services to be cancelled: a set of solid-state electronics or something with moving parts? And I suspect that a lot transformers already have the 3kV tap-off anyway since it's easier to just build one part that can be used on dual voltage or single voltage systems.

It didn't occur to me that the transformers in current single-voltage stock might be easily adapted, but I still think that a special slow-speed/restricted clearance pantograph could be viable solution, especially as it might answer teh same problems elsewhere.

A handful of long distance trains (three isn't it?) powering up the diesel generators they are already fitted with to cross the bridge is not really an issue.

However I doubt that it will only be new rolling stock that would use the bridge, and we all hope that there will be more through workings when there are wires north of the Central Belt. It must be easier to retro-fit an extra (or swap one) pantograph than to fit a battery capable of moving a train together with its associated control gear.

The way things are going, not as much of a fantasy as a 25kV electrification scheme being approved any time soon.

except that this is in Scotland where they have a far better record of improving their railway without the Treasury being able to veto quite so much of the investment that is needed.

 

[NotATrainspott]

It didn't occur to me that the transformers in current single-voltage stock might be easily adapted, but I still think that a special slow-speed/restricted clearance pantograph could be viable solution, especially as it might answer teh same problems elsewhere.
However I doubt that it will only be new rolling stock that would use the bridge, and we all hope that there will be more through workings when there are wires north of the Central Belt. It must be easier to retro-fit an extra (or swap one) pantograph than to fit a battery capable of moving a train together with its associated control gear.

except that this is in Scotland where they have a far better record of improving their railway without the Treasury being able to veto quite so much of the investment that is needed.

Why are pantographs as wide as they are right now? Your gain in loading gauge compatibility may be outweighed by a loss of utility elsewhere on the network. Fitting a second pantograph on an EMU with only one pantograph well sized for a single normal pantograph isn't going to be trivial.

The 379 IPEMU trial demonstrated that batteries could be practically retro-fitted to modern EMUs. In that case, the battery was about half a megawatt-hour and capable of letting the train do entire branch line services on battery power alone. In this case we're talking about enough battery power to get a train moving at up to 80km/h at most for a few kilometres. If the battery modules are spread across the length of the train it would have little impact on each carriage.

 

[Highlandspring]

I suspect so, though seeing as that isn't in any way connected to Network Rail metals it really isn't relevant.

The relevancy may be questionable but the factual accuracy isn’t.

 

[najaB]

The relevancy may be questionable...

Well in that case there's probably a Hornby trainset somewhere closer.

 

[Lucan]

I seriously wonder if the lower members of those diagonal trusses could be removed. The whole thing is massively over-designed

The background to its construction is the Tay Bridge disaster. The original Forth design was to be by Bouch, the designer of the fatal Tay bridge which was still standing when he was asked to design Forth. But then Tay collapsed and Bouch was sacked, and the task given to Fowler and Barlow instead. They made it massive in looks and in fact because that was the mood after the Tay disaster.

But looking at those diagonals it seems that their function is only tensile bracing, to give stability against lozenging of the main uprights. In that case their function could equally be provided by single tensile rods of adequate size, possible by just the upper member of the existing four in each diagonal strut, given the existing over-design. As there are more diagonal struts higher up, maybe the lowest could be removed completely. It would be interesting (and relatively simple compared with modern structures) to do a stress analysis. It is quite likely a modern computer model of the existing structure already exists and would just need a tweak. It would hardly alter the wholesale appearance of the bridge, but the cost of the physical work might be prohibitive, although perhaps less than the alternatives.

 

[najaB]

It would hardly alter the wholesale appearance of the bridge, but the cost of the physical work might be prohibitive, although perhaps less than the alternatives.

I think it would be a non-starter, given the bridge's listed status.