Chiltern Main Line possible max speed?

[NotATrainspott]

Looking at Google Maps it seems that the majority of the CML has reasonably large radius curves and reasonably not-short distances between stations. When the line is electrified, and given new EMUs, what would be the maximum feasible non-tilting speed? If it were possible to be upgraded to 200/225km/h in places, and then connected to OOC at one end (and thence to Paddington) via the NNML and to Birmingham International/Interchange at the other, it could be a consolation for the months/(small number of) years of HS2 construction.

 

[The Planner]

I will trot out the stock answer here. Structures, embankments, track, signalling etc... South of Princes Risborough there are sections that could probably do 125 but not many, north of there i think there will be issues with the embankments as they are apparently weaker than normal due to the construction materials, alledgedly made up of ash even though it is dead straight. North of Banbury the same issues occur, the 75mph island around Fenny is being looked at currently to see if it can get up to a ton.

 

[MarlowDonkey]

If you just wanted extra capacity, a rebuild of the GCR from somewhere north of Aylesbury might be plausible to however far north you wanted to take it . The former GCR route is earmarked for HS2 anyway.

The plausibility of quadrupling the line to South Ruislip remains to be seen, but the Tesco tunnel at Gerrards Cross has the space and the intermediate stations were mostly built to accommodate a four track formation. Beyond that you could use the mostly disused line via Greenford to Old Oak Common with a terminal there as in HS2.

 

[RochdalePioneers]

As a sometimes user of an intermediate station (Denham) my observation of this line is that the speed increases have created major capacity issues. Most of the time I travel to Denham on business (every couple of months) its now usually a very fast non-stop ride to Gerrards Cross then a taxi back past Denham station to my destination then the same again in reverse.

Denham used to have two an hour off peak now only one, and that's the one that doesn't fit meeting times. Both services used to be busy, the remaining one is busier. Can we not add through tracks into more stations when it used to be a 4 track railway?

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[mr_jrt]

The problem, as always with the former GCR, is Marylebone. You could invest in quadrupling the line, but the trains would have nowhere to terminate. This is why I advocate Crossrail branching from OOC to High Wycombe/Oxford/Milton Keynes/etc. These services could them be removed from Marylebone, freeing up capacity for more 'Mainline' services, not to mention, more services via Amersham, potentially enabling the Met to be cut back and the fast lines handed over to NR for conversion to OHLE down to Marylebone.

 

[swt_passenger]

If you just wanted extra capacity, a rebuild of the GCR from somewhere north of Aylesbury might be plausible to however far north you wanted to take it . The former GCR route is earmarked for HS2 anyway.

No it isn't. As a proportion of the overall route north of Aylesbury the section that goes anywhere near the former GCR is trivial. Less than about 5%, and even then it doesn't overlay the actual route, as the GCR curve radius is too tight.

This is absolutely clear from the maps on the DfT website.

 

[RochdalePioneers]

The problem, as always with the former GCR, is Marylebone. You could invest in quadrupling the line, but the trains would have nowhere to terminate.

The trains already run to Marylebone. With the previous stops removed so that they don't get in the way of the various expresses. Add in more station loops and the shorter services could stop at the stations they stopped at until the December timetable change last year.

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[NSEFAN]

If you had a serious budget, you could probably quadruple all the way from West Ruislip to Marylebone, opening up the platforms which were never completed.

 

[455driver]

A higher maximum speed is pointless unless it is going to be sustained for a lot of miles.

Having the whole line able set at 80 would be much better than most of the line at 60 with the odd little bit at 125.

People are obsessed with 'faster is better' but unless those speeds are sustained for miles you will only save a minute or two but use a lot of energy getting up to the higher speed and a lot of brakes getting back down again.

Higher cruising speeds are where the time savings come into play.

 

[route:oxford]

A lot of brakes getting back down again.

Surely with an electric unit (Chiltern electrification suggested by the OP) - this doesn't matter so much as it'll go back to the knitting.

 

[3141]

If you had a serious budget, you could probably quadruple all the way from West Ruislip to Marylebone, opening up the platforms which were never completed.

It was quadruple from West Ruislip to South Ruislip. From there to Marylebone it was twin track. At Sudbury Hill Harrow, Sudbury & Harrow Road, and Wembley Stadium there were two platform faces and two fast through tracks. During "total route modernisation" in about 1990 the arrangements at the first two were changed and it would now require major work to re-instate the fast tracks, At Wembley Stadium it would have been possible but I'm not sure if that's still the case since I haven't been there since they built their Wembley depot. South of Finchley Road there are the twin track tunnels. I've read conflicting accounts about whether a second tunnel was built in readiness for additional traffic, or not. There's a second tunnel entrance at the northern end but I don't know how far it extends. Near the southern end there were more tracks for goods operations but I don't know how far north they extended or how much space for them exists today.

 

[455driver]

Surely with an electric unit (Chiltern electrification suggested by the OP) - this doesn't matter so much as it'll go back to the knitting.

Not as much as most people think!

They are diesel at the moment and that is what I was basing it on, when it is all electrified fair enough but until then!

 

[MarlowDonkey]

It was quadruple from West Ruislip to South Ruislip.

You don't run to Marylebone. If you are building a new route and HS2 isn't happening, you reinstate the line parallel to the Central and the A40 which comes out at Old Oak Common. You could terminate there for connections to Crossrail or continue to Paddington. That was the London to Snow Hill route in the days of the Western Region and the GWR before that.

If HS2 is built, the plan was for it to go alongside or underneath the Chiltern route through the Ruislips before striking off towards Amersham from Denham.
Construction would likely be disruptive to the Chiltern line and probably the Central Line as well.

 

[NotATrainspott]

Upon further research it appears that connecting the Chiltern line to Birmingham Interchange will be simple as well. Just reopen the Kenilworth-Berkswell connecting line, which is currently a cycle path without any development obstruction, and it's basically done. It would mean going to New Street rather than Moor St, which could be an issue.

 

[The Planner]

Except HS2 will be sat on top of most of that...

 

[NotATrainspott]

Except HS2 will be sat on top of most of that...

I didn't realise just how close the two are! It isn't on top of it for most of it, more like parallel, but it does take over the section that goes through the village of Burton Green for a green tunnel.

CFA 18 map book: Stoneleigh, Kenilworth and Burton Green (Ref: ES 3.2.2.18) [Page 37]

Well that might be the end of that idea then.

 

[edwin_m]

I don't think it would be necessary to divert Chiltern services to Birmingham Interchange for links to HS2 when they will already have these links at Moor Street.

 

[IKBrunel]

Surely with an electric unit (Chiltern electrification suggested by the OP) - this doesn't matter so much as it'll go back to the knitting.

Once you've considered the losses in the OHLE, 25kV stepdown transformer, the power electronics, the motor itself, mechanical losses between motor & rail, aerodynamic losses... Then double them because the energy goes back more or less the same way for braking. I would hazard a guess that the energy recouped is in the order of 40%. Would vary hugely depending on gradients,loading, speeds, whether recouped energy is used by another unit on same OHLE (& distance between braking & accelerating units) or is exported back to public distribution network.

Worth doing nowadays with modern power electronics available, but there is still a significant net power consumption to accelerate & decelerate ~100t of EMU

 

[edwin_m]

Once you've considered the losses in the OHLE, 25kV stepdown transformer, the power electronics, the motor itself, mechanical losses between motor & rail, aerodynamic losses... Then double them because the energy goes back more or less the same way for braking. I would hazard a guess that the energy recouped is in the order of 40%. Would vary hugely depending on gradients,loading, speeds, whether recouped energy is used by another unit on same OHLE (& distance between braking & accelerating units) or is exported back to public distribution network.

Worth doing nowadays with modern power electronics available, but there is still a significant net power consumption to accelerate & decelerate ~100t of EMU

As a rule of thumb regeneration generally reduces power consumption by 15-20% - top end of the range for suburban and rather less for long distance.