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Author Topic: Didcot Grade Separation – A Crayonista’s Vision  (Read 8907 times)
Oxonhutch
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« on: March 17, 2017, 12:56:51 pm »

A grade separation of the Didcot avoiding lines (Up and Down Oxford) and the GW Main/Relief Lines is required to relieve this traffic pinch point, now that Reading has been addressed. Because of the visual impact of a large railway fly-over and the proximity of the Ladygrove Estate and central Didcot to the actual confluence, it is proposed that the structure be sited some distance to the east in Moreton Cutting, currently the site of a GWML electrification lay-down area, and extending east thereof.

On the present formation between Didcot East Junction and Moreton Cutting there is space for five roads, four currently exist and the fifth is the position of the long-lifted Up Goods Loop. Provision for this fifth route exists over Marsh Lane Bridge and under South Moreton Bridge.

In this vision, grade separation takes place east of South Moreton Bridge and five separate routes run between Didcot East Junction and Moreton West Junction.  They are (from north to south): Up Oxford, Down Oxford, Down Relief, Up Main and Down Main.  There is no Up Relief. The Down Oxford and Down Relief are bi-directional.

There is complete grade separation with no running conflicts on any of the above routes. Up local trains from Didcot platforms 3, 4 or 5, and freight traffic from Didcot Yard must normally wait for a path on the Oxford lines and cross on the flat to the Up Oxford. At Moreton West Junction they diverge onto the Up Relief. From this point, until Moreton East Junction there are six roads comprising pairs of Reliefs, Oxfords and Mains.

Should there be conflicting traffic on the Oxford lines, Up Locals and Freight can travel wrong road on the bi-directional Down Relief as far as Moreton East Junction where they will cross-over onto the Up Relief.  This route is grade separated from the Oxford Lines.  In addition, if there are conflicts on the Up Oxford and Down Relief, Up Locals and Freight can travel wrong road on the bi-directional Down Oxford and diverge at Moreton West Junction onto the Up Relief, or continue wrong-road on the Down Relief to Moreton East Junction.

In the down direction, there is additional flexibility in the lay-out. Down Oxford semi-fasts calling at Didcot Parkway will route from the Down Oxford to Down Relief at Didcot East Junction or further east at Moreton West Junction. Down Oxford freight traffic avoiding Didcot will route from the Down Relief to the Down Oxford at Moreton West Junction.

Down freight entering Didcot Yard from the Down Relief will not block Down Oxford traffic. Down Freights can also enter Didcot Yard directly off the Down Oxford having crossed over from the Reliefs at Moreton West Junction. This routing keeps the Down Relief free for local traffic in both directions, and in extremis, Down Oxford fasts can route via the Down Relief, Didcot Parkway and the Chester Lines to Didcot North Junction – this is a slow route with 25 mph cross-overs, but it avoids a complete freight blockage for Oxford-bound traffic.

Also provided are routes for Up Expresses to call at Didcot Parkway platform 3 (whist being overtaken on the Up Main?). On departure these can cross back over onto the Up Main without conflict with an Up or Down Local – routing platform 4 or 5.  In addition there is a single-lead crossover from the Mains to the bi-directional Down Relief at Moreton West Junction that would see most use during weekend engineering closures.

Edit: Correct typos on diagram and signalling error
« Last Edit: March 17, 2017, 03:41:44 pm by Oxonhutch » Logged
ChrisB
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« Reply #1 on: March 17, 2017, 01:19:31 pm »

Be interested in the cost of this...looks as though Didcot East car park & the club has to go?
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Oxonhutch
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« Reply #2 on: March 17, 2017, 01:43:21 pm »

Be interested in the cost of this...looks as though Didcot East car park & the club has to go?
Not at all. The whole layout west of Moreton Cutting fits entirely within the current railway footprint- bridges included (please refer paragraph 2).
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IndustryInsider
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« Reply #3 on: March 17, 2017, 01:58:03 pm »

The 'kink' in the lines through the station is just grammatical and not what would be evident on the ground.

Didcot is now a major pinch-point on the GWML.  I've mentioned it in several posts over the years.  This has been highlighted even more since the Reading rebuild got rid of many conflicts, but like a river diversion to alleviate flooding, you often simply move the problem further down stream.  Didcot is now that down stream location, and it is set to become worse when an up to six additional train movements per hour through the area come to fruition with the IET timetable.  It is difficult to believe that Didcot East Junction used to be a single lead junction until 2002.  Since then, not only have passenger train movements increased, but at a guess I would say there are getting on for double the number of intermodal freight trains, only partly countered by a slight reduction in other freight (I'll discount removal of the coal traffic as that didn't normally affect the eastern end of the station).

It's great to see a diagram like this surface and it realises pretty much what I thought might need to happen.  Can I ask whether it's official, unofficial, your own work, Oxonhutch?

Top marks for whoever drew it though as it does address many of the issues that are now causing delays, including the very slow access of freight into Didcot Yard that can block arrivals into Platforms 3/4/5 or trains headed onto the Down Avoiding Line from the east by by five or so minutes as they snake slowly into the yard.  If any way of addressing the same issue for westbound departing trains from Platforms 4/5 could be factored then that would be all boxes ticked in my opinion, though I appreciate the ability to hold freights on the Down Relief until a suitable time slot without getting in the way of other traffic will partly alleviate that problem as well.

The land take would all be agricultural I think, so that increases the feasibility of it happening markedly, though of course it will still no doubt not come cheap.  It is needed though as long standing grade separation at similar locations on other lines, such as Rugby, as well as more recent installations at Reading, Norton Bridge and Hitchin demonstrate how much more flexible things become.
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John R
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« Reply #4 on: March 17, 2017, 02:14:06 pm »

If any land were to be required then agricultural land is pretty cheap at c£8k per acre.  So loose change in the scheme of things.

I agree it's an excellent diagram and (to my untrained eye, well thought out).  If the number of intermodal trains continues to increase then the relief lines are going to become less available for passenger traffic, especially nippy 387s, so this would also enable them to use the mains if required, as the time difference between them and an 800 between Reading and Didcot will be next to nothing.

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Oxonhutch
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« Reply #5 on: March 17, 2017, 02:26:56 pm »

Thanks for your kind comments II. It is entirely my own work, born of too many hours (aggregated over seven years) waiting in Up or Down local trains for conflicting traffic; trying to get my head around some of the seemingly perverse decisions made by the TV signaller or his/her computer – and often missing my HST connection in the process.  Too many hours staring out of the window looking at the formation and wondering what might fit and imagining the moves and conflicts. 

So Atkins, Westinghouse, Siemens, etc. : you saw it here first – please remember that  Smiley. Details of my consultancy rates can be had via the webmaster – who will get a cut!

For cost reasons, the layout is constrained to five roads between Didcot and Moreton.  I feel that the lack of an Up Relief is mitigated by up slow trains being held in a platform or the yard, and there is the back-door route via the Down Relief. A full separation would require a second fly-over like Airport Junction and my feeling is that it would not pass a cost-benefit threshold.

I have just spotted a signalling error courtesy of cut and paste. Platform 4 Up Starter should not have a route 2.
Corrected
« Last Edit: March 17, 2017, 03:42:43 pm by Oxonhutch » Logged
stuving
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« Reply #6 on: March 17, 2017, 03:44:38 pm »

The Western Route Study does propose such an option as likely to be needed, coupling it with quadrupling the Didcot-Oxford line*. The flyover is costed separately, and the damp finger said 50-100M. They describe it as "grade separation at Didcot East Junction to allow trains from the Great Western Down Main to cross the Great Western Up Main without conflict". That sounds like just a single track flyover, with whatever happens between that, the Reliefs, and the Avoiding/Oxford lines staying flat.

I do wonder about that NR proposal, given that there is no suggestion of quadrupling Didcot-Swindon. The headcount of services, including the extra ones for East-West Rail and goods, does give you more on Oxford side. Since the flat junction (much as it is) can be seen as the relabelling of "Relief" as "Oxford" Lines, it's not clear to me that unflattening just the crossing of the Up Main would serve. (Note the official naming of lines is different from this, and from Oxonutch's version.)

Network Rail do seem to believe that only Main Lines ever need grade separating, and can be seen at Reading. That makes sense if the number of relief services is limited to the number of stoppers (say 4 tph max) plus the odd goods. All the rest will be "fast" in that sense. I don't think that works at Didcot. About the only simplification I can see is that there can't be many local stopping services through Didcot towards Swindon - because there are no local stations for them to stop at (currently).

At Reading, the Festival Line is only accessible from the Reliefs (with conflict in the Up direction at Reading West Junction) or by switching over out at Tilehurst East.  So for maximum capacity, do your XC trains use the Festival Line to cross the Mains at Reading and use the Reliefs to/from Didcot? Or do they use a new flyover at Didcot to access the Mains there - but then Up trains conflict with the Down Main of the Reading flyover to get to P3/7/8? Or do Up and Down trains do it different ways? Hardly efficient either.

I would look at changing Didcot station too, so as to have two platforms for each of the Up and Down Swindon lines, and ideally to for each of the Oxfords as well. Note that a further suggestion in the Route Study is for at least one platform and third line on the Avoiding route, which would count towards that. It would also remove the need for quite so much concentrated track swapping at Didcot East.

* Note grade separation at Oxford North is proposed as an alternative to the four-tracking. That looks odd, but I think it's to do with needing the shuffle trains between platforms at Oxford either north or south but not both. Having four tracks that are not needed for capacity - the driver is more speed difference with so much goods traffic - allows this shuffling with only flat junctions. That's similar to the above point about the Didcot station layout.
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« Reply #7 on: March 17, 2017, 04:04:07 pm »

4-tracking Didcot to Oxford and platforms on the avoiding lines have been talked about for a very long time now.  I first remember seeing serious proposals at the end of the last century.  To my mind, that would be the wrong place to spend the money.  Improvements are currently ongoing for this section of line, 4-aspect signalling and bi-directional working is currently being installed to coincide with the closure of Oxford Panel, and the scale of engineering required through the three stations, two River Thames crossings and on adjoining land would be very costly, particularly between Didcot and Radley.

IMHO money would be much better spent on a project such as Oxonhutch describes, along with perhaps separation at Didcot North Junction and possibly a partial 4-tracking where the surrounding landscape doesn't present too many challenges between Oxford and Kennington, or perhaps Radley if the money were available. 

Oxford North Junction grade separation would possibly make sense if and when East-West Rail starts and depending on where its trains originate from, but the layout is set to improve dramatically with the Oxford Corridor Phases 1 and 2, so I'm not convinced of the pressing need for that.

The most crucial area by far is Didcot East Junction.
« Last Edit: March 18, 2017, 09:30:57 pm by IndustryInsider » Logged

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Adelante_CCT
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« Reply #8 on: March 18, 2017, 04:21:12 pm »

Well done Oxonhutch, as II says, pretty much ticks all the boxes. A simple but well drawn diagram which is very well thought out and pretty much keeping within existing boundaries. I like the down relief idea of being able to hold freights if needed.

NR could certainly do a lot worse than following a design of this nature. And even if not, it would appear you have predicted the future, 22 signals and all set to red, typical signal failures!

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Electric train
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« Reply #9 on: March 19, 2017, 09:29:46 am »

Knock on effect of the Reading rebuild which did not surprise the railway planners

The other scheme which is quietly sitting in the background is Southcote junction grade separation.
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Gordon the Blue Engine
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« Reply #10 on: March 19, 2017, 05:47:38 pm »

Southcote Junction grade separation would be good, but having spent quite a few hours on Albert Ball’s Reading signalling simulation I think a trailing crossover between the Down and Up Westburys just West of Southcote Junction and associated bi-directional signalling on the Up Westbury through Reading West would bring useful benefits at less cost.

It is currently possible (assuming the simulation is accurate) to bring a train from the Up Basingstoke along the Down Westbury into Reading P’s 1, 2, 3 and 7, while allowing a parallel move from the Up Westbury on to both Feeder lines and P8.  (I’ve done this on the simulation and had a northbound XC passing an eastbound stone train through Reading West!).

A crossover as suggested above would allow Down trains from P’s 7 and 8 and both Feeder lines heading for Theale to use the Up Westbury to beyond Southcote Junction, thus allowing a parallel route to be set up to/from Basingstoke along the Down Westbury to/from P’s 1, 2, and 3.

I’ve obviously got too much time on my hands…..
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IndustryInsider
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« Reply #11 on: March 19, 2017, 06:04:01 pm »

It is currently possible (assuming the simulation is accurate) to bring a train from the Up Basingstoke along the Down Westbury into Reading P’s 1, 2, 3 and 7, while allowing a parallel move from the Up Westbury on to both Feeder lines and P8.  (I’ve done this on the simulation and had a northbound XC passing an eastbound stone train through Reading West!).

I don't think that is possible in real life.  I'm pretty sure there's only one route from 2810 signal and that's towards 2806 on the Up Westbury.  2804 signal (and 2800) in the Up direction on the Down Westbury are only used as a turnback and consequently very rarely used.  That's not to say such a routing could not be provided in the future though, as all the infrastructure is there on the ground.
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Adelante_CCT
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« Reply #12 on: March 19, 2017, 06:32:23 pm »

Quote
...spent quite a few hours on Albert Ball’s Reading signalling simulation
Who's simulation?  Roll Eyes    Smiley

Quote
It is currently possible (assuming the simulation is accurate) to bring a train from the Up Basingstoke along the Down Westbury into Reading P’s 1, 2, 3 and 7, while allowing a parallel move from the Up Westbury on to both Feeder lines and P8. 

II is correct, that is not possible, a limitation with the game/I don't think i set up routes correctly. I have a version 2.0 if you're interested?
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Adelante_CCT
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« Reply #13 on: March 19, 2017, 07:44:27 pm »

Quote
Southcote junction grade separation
Far easier to do than the Didcot one, although that only eliminates half the problem, with Oxford road junction being the other half which is far more difficult to sort out.
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Gordon the Blue Engine
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« Reply #14 on: March 20, 2017, 09:11:23 am »

Quote
...spent quite a few hours on Albert Ball’s Reading signalling simulation
Who's simulation?  Roll Eyes    Smiley

Quote
It is currently possible (assuming the simulation is accurate) to bring a train from the Up Basingstoke along the Down Westbury into Reading P’s 1, 2, 3 and 7, while allowing a parallel move from the Up Westbury on to both Feeder lines and P8. 

II is correct, that is not possible, a limitation with the game/I don't think i set up routes correctly. I have a version 2.0 if you're interested?

Yes please, what's the link for the download?

Thanks.

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