Short sighted building (again)

[Chameleon]

I read in the paper about 8 new bridges are getting built for the new borders railway. Trouble is, they are all being built to take a single line.

Now this just smacks of lack of forward thinking. Would it really cost much more to build bridges a bit wider that could be used for doubling at a later date? It'll cost 10 times as much to rebuild them in years to come if or rather when they come to upgrade the route due to traffic levels.

 

The same happened on the Bathgate line when it was originally reopened. To save a few quid, they singled part of the line so they could get away with building one platform at the stations. They ended up widening the track ed at huge cost and works to redouble it when it reopened fully.

 

I think the same will happen in the borders. It's a bit like building a new road that's unsuitable for coaches or lorries and only has a few passing places. In other words the absolute bare minimum they can get away with.

['CHARD]

The problem here is that there's a vicious circle in the business case justification for new lines.  The cost of new build or reinstatement has a ceiling beyond which the net benefit is insufficient to justify the project.  Hence, the infrastructure ends up being built down to the minimum specification required to run the service at the levels used in the business case.

 

For the Borders Railway, the service pattern is based on a demand prediction and revenue expectation that justifies a mainly single line with long dynamic loops.  Where possible, the dynamic loops avoid (stop short of) expensive new structures to save the cost of them being built for double track.  I would agree however, that structures like the proposed concrete box under the A7 at Falahill would be better built double width at the outset, with echoes of Victorian can-do foresight.  

 

Reused structures are in the majority on the rejuvenated line, however, gauging issues for modern C3 profile stock may predicate single-tracking for the purposes of clearances.  This would definitely apply to extension south of Hawick through Whitrope.

[phil-b259]

Single lines do not represent a major bar to service frequencies providing the loops are dynamic and suitably placed. As far as the borders project is concerned the infrastructure will allow a more than adequate 30 minute interval service in the peaks - which is exactly what the Uckfield line in Sussex can cope with. Naturally that restricts excursions to off peak times and weekends but since when do railtours run at 8:00 on weekday mornings.

 

If you are concerned about freight - you need to get real - the borders itself has no freight potential and there absolutely zero chance of the line ever being extended back to Carlisle - too many important and costly to replace structures have gone south of Hawick. That is why overall the line is being built to W7 gauge (though the all new bridge structures will be OK for wires and W9 thanks to current minimum design standards)

 

Therefore the solution being built is more than adequate  for future needs

['CHARD]

 many important and costly to replace structures have gone south of Hawick. 

 

That will be these then:

 

Teviot viaduct: http://www.scotlandsplaces.gov.uk/record/rcahms/95710/hawick-teviot-viaduct/rcahms?item=429870

 

Lynwood viaduct: http://www.flickr.com/photos/peteredin/9331504396/ or http://www.rcahms.gov.uk/image/src/171/171_SC698637.jpg

 

Sandholm  viaduct: here, at 0.45 

 

Liddle viaduct: http://canmore.rcahms.gov.uk/en/site/91669/details/liddel+viaduct/

 

 

I'd certainly put the demolition of this quartet in the cripplingly short-sighted category.

[Danemouth]

Sorry chaps - excuse my ignorance, but what's the difference between an ordinary loop and a dynamic one please?

 

TIA,

 

Dave

[rovex]

Same argument applies to the loop being put in on the Redditch/Barnt Green section of the Cross City line, it seems to have been chosen because it doesn't involve rebuilding any bridges.

[caradoc]

A dynamic loop is one long enough for 2 trains to pass without (in theory) either having to stop, or at least wait for the other train.

[multiprinter]

A dynamic loop is one long enough for 2 trains to pass without (in theory) either having to stop, or at least wait for the other train.

 

In simple English, a section of double track.

[black and decker boy]

IS the track bed iteself being rebuilt fro double track or single line? The structures may be irrelevant if it is only single (loops excepted) as the disruption to rebuild the track formation, new drainage etc to double later will be worse than a few bridges.

 

I am sure those responsible are doing as much future proofing now as can be acheived within the budget. There are alway longer trains if capacity with 2 car units does fill up quickly (if units can be found and subsidy justified).

[phil-b259]

Sorry chaps - excuse my ignorance, but what's the difference between an ordinary loop and a dynamic one please?

 

TIA,

 

Dave

 

In the case of a 'standard' or 'conventional' loop. Its length will be designed simply to accommodate the length of a single train. What this means in operational terms is that  when two trains are scheduled to pass then one has to decelerate then come to a complete stand within the loop then accelerate away again once the other train has passed. Thus the train that has to stop incurs a time penalty - which is made worse if the train it is due to cross is running late trapping it in the loop for longer.

 

A Dynamic loop by contrast is one where neither train has to stop or slow significantly to let another pass thanks to the length of the loop. Basically the entry and exit points are such that if running to time the trains will pass each other halfway along the loop Thus each train should never have to slow because in theory the exit signals from each loop will be set to Green before the trains get to the associated distant signal (where they would have to start braking if the exit signal was at Red).

 

While in some locations they are akin to a short section of double track, its worth noting Dynamic loops can also be used in conjunction with a conventional main line. In this case a 60mph freight for example can be sent into the dynamic loop and continue to travel along at 60mph while an express passes on the main line at 125mph, before the freight rejoins behind - again maintaining its 60mph speed. This is advantageous because freight trains tend to be heavy things which take ages to get up to speed so it makes sense to keep them rolling if possible. In fact sometimes it is better off to keep a freight going rather than put it in a conventional loop because of the slow entry & exit speeds they usually entail

[The Stationmaster]

I worked additional dynamic loop capacity into my review stage of the Western Valley (Ebbw Vale) reinstatement scheme as it would have allowed an increased service frequency plus possible reopening to Abertillery with no extra cost at a later stage.  However it was rejected because of the increased initial capital cost.

 

But I did succeed with the pair of loops between Wantage Road and Challow on the GWML which I worked into my infrastructure spec for the Avonmouth - Dicot coal flow (and return empties).  In that case it was possible for a loaded coal train to leave Swindon about 2 minutes ahead of the absolute margin in front of an HST and come out of the loop at Wantage Road immediately behind it without having to stop.  But planning dynamic loops properly means taking very careful of margins between trains of differing speeds and also carefully considering overlaps at the exit from the loops - great fun with a large sheet of graph paper if you're into the old-fashioned way of headway calculation and working out regulating margins properly  (and even more enjoyable when you're being paid to do it ).

[Danemouth]

Thanks all for the information on Dynamic loops - I found it most interesting - you live and learn!

 

Regards,

 

Dave

[jjb1970]

I think it is easy to criticise stuff like this without appreciating the position of those who have a budget and have to deliver something within that budget. I'm guessing the people making the decisions don't like single lining structures any more than anybody else and may well have argued for more money. However if they've been told that the budget is what the budget is then they have to deliver something with what they have. I see the same all the time with military procurement, in my experience the true culprits usually escape opprobrium and leave those lower down the food chain to take the heat.

[Chameleon]

I also wonder if, when they come to lay the track, they will run it up the centre of the trackbed or keep it to one side? There are pros and cons both ways. It would be easier to double the line (or at least extend the dynamic loops) without disturbing the track that is already laid.

Alternatively, if it is run up the middle, it'll be easier to electrify at a later date due to more clearance under arched bridges.

[The Stationmaster]

I think it is easy to criticise stuff like this without appreciating the position of those who have a budget and have to deliver something within that budget. I'm guessing the people making the decisions don't like single lining structures any more than anybody else and may well have argued for more money. However if they've been told that the budget is what the budget is then they have to deliver something with what they have. I see the same all the time with military procurement, in my experience the true culprits usually escape opprobrium and leave those lower down the food chain to take the heat.

Absolutely - we faced exactly the same situation with the Avonmouth scheme where we would ideally have liked to continue the double line reinstatement right through to Stoke Gifford and it was possible to make the operational case to support that work.  However the budgetary impact would have been massive for a variety of reasons and I knocked it out of the scheme because I knew we would never get the money for it.  

 

Similar things occured on the devlopment work for CTRL/HS1 where the original layout flexibility proposals for St Pancras were so complex that - after we'd produced scheme plans to enable detailed estimates (I was then off the big railway and with a signal engineering company) 'the project' decided on a massive reduction in scope in order to keep the costs within budget, and delivered what is there today, and never mentioned that they'd changed anything (which also goes on with large schemes).  

 

I suspect too that something similar might have gone on at Reading where things seen in early 'artists impressions' haven't appeared in what seems to be the final result.  Generally on BR it was ok if you could get it approved within the scheme tolerance or by going for re-authorisation but if those courses weren't available then it invariably meant a reduction in scope.  This also explains, I think, why some Govt schemes, in particular, tend to overrun their original costings - the original scope is reduced to get the scheme through The Treasury and then bits are put back in which come out as cost overruns although I bet the bigger culprits are the 'dabblers' who just keep fiddling with the original spec?

[jjb1970]

The bain of my life is juggling figures between purchase and operational budgets. The people who buy warships are not the ones who operate them and the budgets are entirely separate. So it promotes purchasing ships built of lower grade steel to reduce purchase cost and helps the program budget. Everybody knows that this pumps up the through life costs by massively more than what they save on the up front cost but those through life costs come off another budget so it doesn't matter. Well it does matter, because tax payers pick up the tab but I really do not condemn the guys who make these decisions as they're being beaten up badly to cut their costs and stay within an arbitrary budget. Or time and time again rather than leave space to accomodate upgrades and growth (warships always end up carrying way more than they were designed for) they're built down to cost with minimal growth potential with catastrophic impact on costs to incorporate upgrades later on. At least the RN have learned that lesson as the T45 and QEC were both designed with plenty of margin for growth but I've seen some warships that are on the limit of their stability when they leave the yard and end up dumping some of the expensive toys as they're just not sea worthy.

[Grovenor]

A dynamic loop can be seen in action towards the end of this video, very accurately timed too.

http://www.rmweb.co.uk/community/index.php?/topic/78479-greeley-layout-astonishing/

Keith

[The Stationmaster]

A dynamic loop can be seen in action towards the end of this video, very accurately timed too.

http://www.rmweb.co.uk/community/index.php?/topic/78479-greeley-layout-astonishing/

Keith

Not really - the loop appears to be little longer than a train whereas a proper dynamic loop involves both trains running on green aspects all the way.  Hence in a UK situation a dynamic loop is inevitably going to be several miles long unless linespeeds are very low.  Once you build in a full overlap at the exit signals plus their repeaters sited at full braking distance in rear of them then add the clearance times at both ends plus a margin time of at least a couple of minutes and even at only 60 mph the distances soon build up.  Ane even if it is acceptable to allow for asingle yellow in rear of the exit signal you are still going to be talking in terms of miles.