I doubt making a NR train compatible with standard 4th rail is ever going to be economically viable. Absolute best you would get short of converting to OHLE is converting the 4th rail to the same setup as the end of the Wimbledon branch or the Bakerloo north of Queens Park with bonded 3rd rail and then using standard dual voltage trains. That won't give you any of the performance benefits of converting the fast lines to OHLE, but it would be cheap to do as a first step.
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Chiltern Railways Electrification Programme
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But then we'd be bringing in third, plus perpetuating fourth, and then presumably AC on the mainline - with a view to connecting into AC at Oxford, Bletchley etc. Feels messy.
Don't get me wrong, I firmly believe OHLE is the way to go, but in the interests of making the dish palatable, you have to come up with an acceptable halfway house in order to get there. Bonding the 4th rail lets Chiltern use standard dual voltage trains and maintain the Met service initially. You would install OHLE between Aylesbury and Amersham. You then cut the Met back as you convert each section back to Moor Park to OHLE, and then you cut the residual Met service completely and convert the fast lines to Harrow to OHLE.
Perhaps you just leave the Chesham branch with bonded 3rd rail as that's about all the expenditure that can be justified, and when the equipment is life expired, thats when it goes over to battery units, charged from the OHLE in the bay at Chalfont. That would buy time for train batteries to improve further whilst maximising the return on any spend. Also means that you don't need to immediately fit a chunk of the Chiltern fleet with current battery equipment for a tiny section of their network.
Trainbike46
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you're making everything unnecessarily complicated; leave the fourth rail as is, install OHLE where no electrification is present, and have the new dual-voltage EMUs for Chiltern be compatible with 4th rail; the difference it would require to the units is tiny. There's no need to change the service pattern (at least not to allow electrification to happen), and what you're proposing would be a downgrade in service that really isn't necessary
So in this instance new OHLE from Neasden to Harrow OTH only - and then fourth rail up? given it is on the fast lines, but not on the NR ones.
And then wires Amersham-Aylesbury VP?
Assuming of course Marylebone-Neasden would be done/part of the core scheme.
Trainbike46
Established Member
Yes, unless it would be cheaper to do OHLE along the whole route, leaving the 4th rail in place for Met line services.
There's definitely no reason to install 3rd rail, or to massively change (worsen) service patterns of the met line in particular
if there's any problem bridges along Neasden-Harrow-OTH, there may be a case for moving the switch-over point from Harrow OTH to Neasden, if you can get safety approval, but that may be easier along existing 4th rail track
If the difference to the units is tiny, then why was the 4th rail bonded north of Queens Park and between East Putney and Wimbledon rather than making simple changes to the rolling stock to make them compatible with the 4th rail? You really don't want bespoke rolling stock, especially when the bonding option is a) so simple, and b) only temporary. Then ultimately Chiltern ends up with vanilla AC rolling stock by removing the shoes, and a considerable amount of obsolete top contact DC electrification gets removed.
You wouldn't want to have OHLE to Harrow, 4th rail to Amersham, then OHLE to Aylesbury. Every pan up/down changeover is an opportunity for something to go wrong, and keeping the 4th rail on the fast lines north of Harrow for so few Met services just isn't sensible.
I wouldn't say it's a downgrade. Ultimately, they'd end up with faster journeys as NR would be able to maintain the infrastructure to a higher standard than TfL is willing to due to the poor top speeds of their s-stock. They'd also be able to run longer trains too, once the platforms are extended, increasing capacity. Passengers north of Moor Park just have to change trains at Harrow if they want Baker Street (or at a station further south like Neasden or West Hampstead, if you built Chiltern platforms there).
ShadowKnight
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What the highest speed that could be theoretically be achieved on 4th rail?
Trainbike46
Established Member
Have you considered that building a unit capable of both 4th rail and 3rd rail is rather more difficult than making a unit that is capable of 4th rail and OHLE?
More importantly, if you want OHLE on the met fast lines, why not just install OHLE directly, instead of mucking about with temporary solutions that only increase cost?
Remember, 4th rail doesn't have the (in)compatibility issues of 3rd rail, as the AC and DC return currents are entirely separate
I never said anything about a unit that works on 4th rail as well as OHLE, not sure where you're getting that from. My argument is bonding the 4th rail means you can use standard 3rd rail trains (or more relevantly, standard dual voltage trains). It is my understanding (and please, correct me if I'm wrong), that all TfL's 4th rail trains work fine on bonded 3rd rail, so the S-stock should just work (let alone the fact it already does so at Wimbledon). Unless you bond the 4th rail to make it compatible with 3rd rail units, you're stuck with using diesel trains until the whole shebang gets OHLE. I guess bi-modes could solve that issue, but still.
The benefit of the temporary state of bonded rail means you can commit to the project in smaller chunks with minimal disruption. You can incrementally bond the rails with zero changes to services, and both the existing Met stock and the future Chiltern stock can use it. Installing the OHLE between Aylesbury and Amersham has no impact to the diesel services, so that's fine. Chiltern stays as diesel, the Met operates as now to Amersham, abet on increasingly bonded 4th rail.
Once you've finished the bonding between Amersham and Harrow and the OHLE between Aylesbury and Amersham, you can then introduce the new dual voltage rolling stock for Chiltern and cut the Met service back. You then convert southwards from Amersham to Harrow at leisure.
I do agree with you, it probably would be cheaper to rip up the 4th rail and install OHLE all in one go, but you'd have to withdraw the Met service and somehow find diesel rolling stock to provide the service between Amersham and Harrow whilst you did the whole project. I think that approach is too risky, you may disagree.
The benefit of the temporary state of bonded rail means you can commit to the project in smaller chunks with minimal disruption. You can incrementally bond the rails with zero changes to services, and both the existing Met stock and the future Chiltern stock can use it. Installing the OHLE between Aylesbury and Amersham has no impact to the diesel services, so that's fine. Chiltern stays as diesel, the Met operates as now to Amersham, abet on increasingly bonded 4th rail.
Once you've finished the bonding between Amersham and Harrow and the OHLE between Aylesbury and Amersham, you can then introduce the new dual voltage rolling stock for Chiltern and cut the Met service back. You then convert southwards from Amersham to Harrow at leisure.
I do agree with you, it probably would be cheaper to rip up the 4th rail and install OHLE all in one go, but you'd have to withdraw the Met service and somehow find diesel rolling stock to provide the service between Amersham and Harrow whilst you did the whole project. I think that approach is too risky, you may disagree.
Overcomes return current issue, but there are other EMC concerns to face mixing the systems in the same vicinity. Not insurmountable, but still costly and possibly disruptive. You have to consider fault conditions for example, signalling equipment compatibility etc. To me, the obvious thing for a new fleet captive to the Chiltern network is to build in 4th-rail DC pickup capability to battery-equipped trains, possibly also with AC overhead capability (maybe sub-fleets of the same basic train with different electric capabilities for different duties). A 4th rail train could plausibly be engineered for future easy conversion to 3rd rail supply rather than being equipped for change-over in service, which would be more complex. That could ensure residual value if redeployed in future to 3rd rail areas. Any small extensions of the ground conductor system would thus best be done with a four-rail configuration. The only significant example I could imagine being acceptable is the section south of Harrow to Neasden closely following parallel Met tracks throughout, but it might also be plausible to put a bit in around Aylesbury in platforms and sidings for layover charging, only energised when an appropriate train is present. LUL feeders would need strengthening as necessary.
A rehash with potential to also serve XC and freight so appeasing the 'bean counters' and ticking green rail boxes could be
Phase 1: Birmingham - Leamington 25kV OHLE ( as part of wider Snow Hill Lines electrification). Introduce EMUs on the WMT services.
Phase 2: Leamington - Aynho Junction - Oxford - Didcot plus Leamington - Coventry 25kV OHLE. Oxford - Didcot was postponed from GWML electrification so bi-mode 80x have to be used instead of 387 EMU for Oxford terminating services.
Phase 3: London Marylebone - Oxford/Aynho Junction 25kV OHLE. This removes needing bi-modes for Birmingham services.
Better of course if Phases 2 south from Leamington and 3 north from Marylebone ran in parallel meeting at Aynho Junction rather than sequential.
Aylesbury is tricky although as stated 4-rail & 25kV OHLE is more compatible than 3-rail & 25kV OHLE. Overall long term cheaper to wire Marylebone - Aylesbury throughout as 25kV OHLE, wire Amersham - Aylesbury as 25kV OHLE and build bi-mode trains or build high battery capacity bi-modes plus charging facilities with no additional electrification ? Long term cheapest pehaps extending 4th rail Amersham - Aylesbury but unless a policy change not permitted.
Now Banbury depot has been expanded because HS2 work will sever Aylesbury - Princes Risborough if that route becomes just a service shuttle then while a very small fleet use battery units.
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