Chiltern Railways Electrification

[HSTEd]

Other than the general benefits of having a TfL-run service (decent trains and simpler fares, which can be achieved with a new BEMU order and Project Oval instead) I don't see how that would bring significant improvements.

Frequency is unlikely to go above 2tph - the only minor improvement possible is extending both trains per hour to Vale Parkway instead of just one. The Met Line S-stock trains are also slightly slower than the class 165s, and have more longitudinal seating, which wouldn't be comfortable if coming all the way from Aylesbury.

Also, while you would get direct trains to Baker Street, King's Cross, Liverpool Street etc, this would be at the cost of gaining extra stops at Finchley Road, Wembley Park and Moor Park, assuming it uses the Met line 'fast' stopping pattern (which is not a guarantee). Marylebone isn't perfect but running fast after Rickmansworth/Harrow is 20 mins faster, making the walk to Baker Street (or changing to the Bakerloo line) quicker than a direct tube service.

If the transfer at Marylebone is improved, through easier access to the Bakerloo platforms, or an easier walking route to Baker Street (avoiding traffic lights etc) it would be faster and cheaper than extending the Met.

I think it's likely that Aylesbury/Aylesbury Vale Parkway would get the two current Chiltern paths north of Harrow and also an extension of the two Amersham terminators. The marginal cost of extending the Amersham terminators would be very low given the low station density north of there and consequently high average speeds.

The line speed on the route doesn't really benefit the diesel units, it's not really much above the capability of S Stock as I recall.

Of course the railway industry benefits by allowing this operational annoyance to be dispensed with, including allowing elimination of significant trackwork, tripcocks and all that comes with them.

 

[Farigiraf]

I think it's likely that Aylesbury/Aylesbury Vale Parkway would get the two current Chiltern paths north of Harrow and also an extension of the two Amersham terminators. The marginal cost of extending the Amersham terminators would be very low given the low station density north of there and consequently high average speeds.

The line speed on the route doesn't really benefit the diesel units, it's not really much above the capability of S Stock as I recall.

Of course the railway industry benefits by allowing this operational annoyance to be dispensed with, including allowing elimination of significant trackwork, tripcocks and all that comes with them.

The complexities of sharing track with the tube would only be eliminated if the two Chiltern paths were also operated by the Metropolitan. Extending the Amersham terminators as well would provide a frequent 4tph semi-fast via Wembley Park, but whether this would be more beneficial than 2tph fast to Marylebone is subjective. Assuming all 4tph would have the same stopping pattern as the existing Amersham Met services, it'd take about 1h 25 to Baker Street, highly competitive with Chiltern. However, some Met line paths with the same amount of stops can take up to 15 minutes longer due to a 10min wait just before Wembley Park. So it could be justified, but it'd be less self-contained (so more prone to delays) and would have to include the cost of electrifying to Aylesbury too, unless a battery can somehow be fitted onto an S8 stock train.

 

[N1]

The complexities of sharing track with the tube would only be eliminated if the two Chiltern paths were also operated by the Metropolitan. Extending the Amersham terminators as well would provide a frequent 4tph semi-fast via Wembley Park, but whether this would be more beneficial than 2tph fast to Marylebone is subjective. Assuming all 4tph would have the same stopping pattern as the existing Amersham Met services, it'd take about 1h 25 to Baker Street, highly competitive with Chiltern. However, some Met line paths with the same amount of stops can take up to 15 minutes longer due to a 10min wait just before Wembley Park. So it could be justified, but it'd be less self-contained (so more prone to delays) and would have to include the cost of electrifying to Aylesbury too, unless a battery can somehow be fitted onto an S8 stock train.

You would need new stock to run to Aylesbury anyway, as there wouldn't be enough S8 stock. Then you can do battery and maybe fit charging at Aylesbury Vale Parkway. It would mean a bit of a LU micro-fleet, but the current arrangement of tripcock fitted DMUs are also a bit of a microfleet (not to the same extent). Complications are usually who owns what and driver training for both NR and LU metals. Advantage if you divert and terminate into Baker Street is releasing some capacity at Marylebone for post Chiltern electrification (however it is done) enhancements.

== Doublepost prevention - post automatically merged: 11 Nov 2025 ==

In terms of calling pattern I imagined it would be the same as a 'Fast' Met service, same as current but with additional calls at Wembley Park and Finchley Road, but of course plenty of scope for variation.

Possibility of a tie-in to Croxley link as well, if that happened you could run battery Met service Aylesbury to Watford, that is much more of a fantasy stretch than realistic proposal

 

[Nicholas Lewis]

I seem to recall that the shared 3rd/4th rail there by Richmond is special. Something about one of the rails being bonded somewhere?

NRs traction return is via the running rails on tube trains its via the 4th rail. So on this section and Putney to Wimbledon the 4th rail is bonded back to the running rails.

Now on the section from Harrow on the Hill this wouldn't be possible so if it was necessary to power the train over this section it would have to be fitted with an additional 3rd & 4th rail shoegear. This is clearly not an issue as LUL trains have them but it does come with an additional risk that on any non LUL route these trains are running over would need to have the sleeper width cleared of any obstructions (which they should be). It also another complication on the train and I would say no point bothering as you can wire upto Harrow on the Hill and then run on battery upto Amersham then revert to OLE. Actually the Aylesbury route is remarkable free of arched bridges so can maximise OLE to keep off ole running as low as possible. This can keep train weight down if you dont need to carry around so much battery storage.

 

[Mikey C]

Frequency is unlikely to go above 2tph - the only minor improvement possible is extending both trains per hour to Vale Parkway instead of just one. The Met Line S-stock trains are also slightly slower than the class 165s, and have more longitudinal seating, which wouldn't be comfortable if coming all the way from Aylesbury.

No toilets also.

Plus, unless Aylesbury station and the tracks south of there were completely segregated, there would still be joint NR/LU usage between the trains going via Amersham, and the ones going via Risborough.

 

[Farigiraf]

You would need new stock to run to Aylesbury anyway, as there wouldn't be enough S8 stock. Then you can do battery and maybe fit charging at Aylesbury Vale Parkway. It would mean a bit of a LU micro-fleet, but the current arrangement of tripcock fitted DMUs are also a bit of a microfleet (not to the same extent). Complications are usually who owns what and driver training for both NR and LU metals. Advantage if you divert and terminate into Baker Street is releasing some capacity at Marylebone for post Chiltern electrification (however it is done) enhancements.

== Doublepost prevention - post automatically merged: 11 Nov 2025 ==

In terms of calling pattern I imagined it would be the same as a 'Fast' Met service, same as current but with additional calls at Wembley Park and Finchley Road, but of course plenty of scope for variation.

Possibility of a tie-in to Croxley link as well, if that happened you could run battery Met service Aylesbury to Watford, that is much more of a fantasy stretch than realistic proposal.

And as a result, you'd successfully integrate the Aylesbury line into the tube network, but with altogether not that many benefits other than freeing up capacity at Marylebone and better connections. However nice it would be, it would be an awful lot of work and quite expensive. Until such funding can be found (which, considering the recent announcement by the transport secretary regarding Chiltern wiring, is a long way away), a DMU replacement and a general improvement of wayfinding around Marylebone is an okay compromise.

 

[HSTEd]

No toilets also.

Plus, unless Aylesbury station and the tracks south of there were completely segregated, there would still be joint NR/LU usage between the trains going via Amersham, and the ones going via Risborough.

Why wouldn't they be fully segregated?
Theres nothing else running on that section is there?

The Aylesbury depot would likely be made redundant by the reduction in fleet strength from eliminating the via Amersham DMU service.

Aylesbury could retain a separate platform for the service via Princess risborough.
Which side of the segregation Aylesbury Vale parkway goes is a question for further discussion.

(EDIT: In any case, a single track to access the depot can probably be provided even if the tube wants to go to AVP)

 

[stevieinselby]

Plus, unless Aylesbury station and the tracks south of there were completely segregated, there would still be joint NR/LU usage between the trains going via Amersham, and the ones going via Risborough.

The Risborough branch feeds into platform 1, the line to/from Amersham feeds into platforms 2 and 3, and the lines diverge immediately on leaving the station. While there is a crossover to allow trains to/from Risborough to use platform 2, it is rarely used and I'm sure could be removed without any great impact on operations – to all intents and purposes, they are almost completely segregated already!

 

[N1]

Before we get too far ahead ripping up track need to account for the possibility of Aylesbury spur connection to East-West Rail. As this is to be reinstated single-track AFAIK then my opinion would be to extend/reinstate Aylesbury via High Wycombe, as MK is also an attractive destination for work and leisure from Buckinghamshire.

 

[Mikey C]

Before we get too far ahead ripping up track need to account for the possibility of Aylesbury spur connection to East-West Rail. As this is to be reinstated single-track AFAIK then my opinion would be to extend/reinstate Aylesbury via High Wycombe, as MK is also an attractive destination for work and leisure from Buckinghamshire.

Exactly. The key connection would be from MK to High Wycombe, so there would be a need for services between Aylesbury and Aylesbury VP from both Risborough (the Wycombe to MK service) and from Amersham.

 

[HSTEd]

Exactly. The key connection would be from MK to High Wycombe, so there would be a need for services between Aylesbury and Aylesbury VP from both Risborough (the Wycombe to MK service) and from Amersham.

If you need services to Aylesbury Vale Parkway from both then there is probably room for a single track each for the Met and the diesels between Aylesbury and Aylesbury Vale Parkway.

AVP to Aylesbury is shorter than Chesham to Chalfont and Latimer after all.

But personally I think the more likely result is the Metropolitan Line just goes to Aylesbury and all trains north of there go via Princess Risborough. Which they would have to do anyway to serve High Wycombe.

Of course EWR probably won't be connecting to the Aylesbury line any time soon.

 

[PLY2AYS]

What shape are they? As I understand it, arches aren't generally too bad to get wires through because they're taller in the middle where the wires need to go, but the square girder type bridges can be much harder.

It’s both through the tunnels frustratingly.

Can’t see why a charging section of overhead wires and 3rd/4th rail can’t both be present at MYB to charge batteries for the tunnels section? Similarly a quick charge platform at AVP or Risborough bay platform would be useful and OHLE in the sidings at Aylesbury

(Of course, speculation on my part but interested to know the answers and complexities this would face)

Use of the LU juice between Harrow and Amersham would be ideal.
Can’t see much OHLE being installed north of there without much deforestation, similarly around Gerrards to Risborough with tunnels potentially needing some work/track lowering at South Harrow, Whitehouse, Brill, Ardleigh and between Risborough and Saunderton on the Up.

That’s not including the lack of headroom of over bridges between West Hampstead and Neasden South Jn. and between Risborough and Bicester South Jn.

Must be a few more conflicting places north of Banbury that I’ve neglected.

 

[SynthD]

Of course, speculation on my part but interested to know the answers and complexities this would face

Discontinuous electrification is still so new we (I?) don’t know the full range of sensible options. As it is crucial for the pan to come down before any obstacles, OHLE for bimodes has been wary of small sections broken up by bridges that would bash an up pan. In theory you can just put in the balise that controls the pan as often as necessary, but for rational, cautious reasons that won’t be done.

Is it plausible for Gerrards Cross station to be four track wide, all electrified, but the tunnel is four track wide, only the middle two are electrified?

 

[zwk500]

Discontinuous electrification is still so new we (I?) don’t know the full range of sensible options. As it is crucial for the pan to come down before any obstacles, OHLE for bimodes has been wary of small sections broken up by bridges that would bash an up pan. In theory you can just put in the balise that controls the pan as often as necessary, but for rational, cautious reasons that won’t be done.

You won't want the pan going up and down like a yo-yo but discontinuous electrification on the Core Valley Lines has had to deal with these problems already. There are solutions like having earthed sections of wire or designing the scheme such that there's decent lengths of either electric or battery/bi-mode operation.

Using APCO with balises is fine where the trains are fitted with the appropriate balise-reading kit, but obviously if trains aren't yet ETCS fitted then that would be another factor to consider. Perhaps by the time Chiltern is electrified it can go hand-in-hand with a digital signalling upgrade.

 

[Trainbike46]

Discontinuous electrification is still so new we (I?) don’t know the full range of sensible options. As it is crucial for the pan to come down before any obstacles, OHLE for bimodes has been wary of small sections broken up by bridges that would bash an up pan. In theory you can just put in the balise that controls the pan as often as necessary, but for rational, cautious reasons that won’t be done.

Is it plausible for Gerrards Cross station to be four track wide, all electrified, but the tunnel is four track wide, only the middle two are electrified?

A more sensible way to go about it, is to identify areas which are suitable for OHLE islands, and provide OHLE for charging at those islands, considering things like:
- Structures that would need adapting
- Ease of getting a power supply
- Battery range
- amount of charging you can get done per amount of electrification you do

So you get a small number of islands were recharging happens, Instead of what it sounds like you're thinking, namely starting with full electrification in principle, and then leaving gaps in places that are "too difficult".

== Doublepost prevention - post automatically merged: 28 Nov 2025 ==

You won't want the pan going up and down like a yo-yo but discontinuous electrification on the Core Valley Lines has had to deal with these problems already. There are solutions like having earthed sections of wire or designing the scheme such that there's decent lengths of either electric or battery/bi-mode operation.

Using APCO with balises is fine where the trains are fitted with the appropriate balise-reading kit, but obviously if trains aren't yet ETCS fitted then that would be another factor to consider. Perhaps by the time Chiltern is electrified it can go hand-in-hand with a digital signalling upgrade.

If you're using new rolling stock, and realistically any new partial electrification scheme would, you can see ETCS fitmet as the default state at this point, I would argue.

 

[HSTEd]

Partial electrification could be combined with an ETCS Level 1LS installation at (comparatively) limited cost in any case.

 

[MarkyT]

Partial electrification could be combined with an ETCS Level 1LS installation at (comparatively) limited cost in any case.

The existing signalling must be coming up for renewal over the next decade, especially the early SSI sections completed in the 1990s route modernisation. NR recently decommissioned the obsolete BR pilot scheme ATP system, replacing it with an enhanced TPWS fitment as an interim solution until something more modern can supersede it.

 

[HSTEd]

The existing signalling must be coming up for renewal over the next decade, especially the early SSI sections completed in the 1990s route modernisation. NR recently decommissioned the obsolete BR pilot scheme ATP system, replacing it with an enhanced TPWS fitment as an interim solution until something more modern can supersede it.

I'm surprised they got permission to replace the ATP system with TPWS,

But something will have to be done soon.

 

[The Planner]

The existing signalling must be coming up for renewal over the next decade, especially the early SSI sections completed in the 1990s route modernisation. NR recently decommissioned the obsolete BR pilot scheme ATP system, replacing it with an enhanced TPWS fitment as an interim solution until something more modern can supersede it.

Chiltern resignalling is a loooong way off.

 

[MatthewHutton]

Now on the section from Harrow on the Hill this wouldn't be possible

Why can’t you do rail bonding between Harrow on the hill and Amersham on the fast tracks like they do into Richmond and north of Queen’s Park on the Bakerloo?

 

[Nicholas Lewis]

Why can’t you do rail bonding between Harrow on the hill and Amersham on the fast tracks like they do into Richmond and north of Queen’s Park on the Bakerloo?

Would require LUL to modify their train detection arrangements to do that. The section involved can be easily covered by battery power if its wired either side.

 

[MatthewHutton]

Would require LUL to modify their train detection arrangements to do that. The section involved can be easily covered by battery power if its wired either side.

Surely they can do that though if it is done on various other lines including the district line which uses the same rolling stock?

And batteries are all well and good but they add weight (and therefore maintenance cost) and are non standard for rail vehicles given how much electrification there is worldwide, which is unlikely to change.

 

[Trainbike46]

Surely they can do that though if it is done on various other lines including the district line which uses the same rolling stock?

That's no point - if you want to use the lul system to recharge batteries, you would fit the new Chiltern BEMUs with fourth rail collection shoes, as that would prevent the need for infrastructure changes, and Chiltern stock doesn't need to be compatible with 3rd rail (unlike the stock on the district line).

 

[MatthewHutton]

That's no point - if you want to use the lul system to recharge batteries, you would fit the new Chiltern BEMUs with fourth rail collection shoes, as that would prevent the need for infrastructure changes, and Chiltern stock doesn't need to be compatible with 3rd rail (unlike the stock on the district line).

Fair enough - makes sense!

 

[Nicholas Lewis]

Surely they can do that though if it is done on various other lines including the district line which uses the same rolling stock?

And batteries are all well and good but they add weight (and therefore maintenance cost) and are non standard for rail vehicles given how much electrification there is worldwide, which is unlikely to change.

If the bulk of Chiltern was electrified you wouldn't need to install big batteries to cover the c15 miles between Harrow on the Hill and Amersham.

 

[zwk500]

Partial electrification could be combined with an ETCS Level 1LS installation at (comparatively) limited cost in any case.

Haven't Network Rail stated they arent interest in L1?

 

[HSTEd]

Haven't Network Rail stated they arent interest in L1?

Yes, meanwhile the ETCS Level 2 programme appears to continue to slide and AWS and TPWS gets ever older and closer to obsolescence.

Beyond that, the railway lacks a credible response to the emergent threat of overspeeding by high power multiple units which seems likely to me to cause a serious incident if nothing is done.

I am not sure this anti L1 position is a good idea in the long run, but that is wandering off topic.

 

[NorthKent1989]

In regards to extending the Met to Aylesbury, in many ways it would makes sense, the current Chiltern service seems to be an express Metropolitan line service.

Of course in the event of the Met being restored to Aylesbury, the S8’s would have to have more traverse seating than currently, and Aylesbury would have to be fast, all stops to Rickmansworth then Harrow then Finchley Road, and possibly Wembley Park seeing as that’s a hub these days