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Bi-Directional Running On Mainline


Yooski
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Hello Everyone,

 

I was wondering when a mainline has bi-directional signalling as a redundancy (so not used all of the time) what signals are placed on the "wrong running line" facing the wrong way and are the signal distances the same?

 

For instance does the wrong running line have ground signals or 3 aspect signals or normal 4 aspect signals?

 

Just looking for inspiration and a reason to run trains on the wrong track either direction :)

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You generally get one of two set ups on bi-directional lines. Either full signalling that is basically a copy of the signalling fitted to the normal running line, so if it 4 aspect in the 'right' direction, it will be 4 aspect in the 'wrong' direction, with signals fitted opposite each other, or a basic version called SIMBIDS (simplified bi-directional signalling). With simbids, you get less signals in the wrong direction compared to the right direction, and these are more often than not 2 aspect signals, yellow/green 'distant', and a red/green 'stop' signals. 

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You generally get one of two set ups on bi-directional lines. Either full signalling that is basically a copy of the signalling fitted to the normal running line, so if it 4 aspect in the 'right' direction, it will be 4 aspect in the 'wrong' direction, with signals fitted opposite each other, or a basic version called SIMBIDS (simplified bi-directional signalling). With simbids, you get less signals in the wrong direction compared to the right direction, and these are more often than not 2 aspect signals, yellow/green 'distant', and a red/green 'stop' signals. 

I used to work Swindon Panel and our lines were SIMBIDS fitted. The signals on the reversible were few and far between and only 2 aspect.

Using the reversible line for overtaking manouvres, of slower trains, used to be a complete :nono: but was authorised a few years ago - the benefits to performance must have been realised! 

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The line between crewe and Wilmslow and crewe and shrewsbury are both bi directional and the ‘wrong direction’ signals are a mirror of the ‘right direction’ ones, the wilmslow line has the same line speed on both lines (100mph) but the shrewsbury line is slower on the wrong direction line

 

The chiltern mainline is bi di between anyhoo and risborough hutvthe bi di line only has 1/2 the signals as the right direction line, once you enter it at risborough it’s a good 8 miles to the next set of signals at ashenden jn

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Would the speed limit be reduced on the "wrong line" due to the signal distances and the fact that they where two aspect?

In the 1980s and 90s the Reading PSB controlled section of SIMBIDS from Foxhall Junction (Didcot West) towards Swindon had speeds of 125mph in the normal direction and 80 or 85mph on the bi-directional. As far as I recall, the only occasion that required cautioning drivers before using the bi-directional facility was if you were going to send a down train on the up line and an up train on the down line (so they would pass each other on the wrong side) but I never saw that done and can’t really think of any good reason why anyone would need to do that.

Edited by Western Aviator
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The Midland Mainline south of Leicester as far as Wellingborough is signalled for bi-di working with equal spacing on both lines, plus the line speed is the same throughout. I've down it several times in the past, usually at night.

Edited by Rugd1022
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A practical example of SIMBIDS as installed in the mid 1980s is shown in files 1A and 1B

 

In this example only ONE TRAIN may proceed on each line through the entire area covered by the SIMBIDS scheme.

 

On todays busy railway this makes SIMBIDS practically useless as a method of keeping the train service going.

post-658-0-40059800-1513295704_thumb.jpg

post-658-0-02622400-1513295724_thumb.jpg

Edited by phil-b259
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And an example where SIMBIDS has been upgraded to the halfway house stage. Not full bidirectional working but more wrong road signals so as to allow up to 4 trains to proceed wrong line at once.

 

A superficial glance would suggest that full bi-directional working has been installed...

 

BUT THIS IS NOT THE CASE!

 

Due to the standards having changed since the mid 1980s we are not allowed to have some signal configurations today which were permissible back then. Hence the appearance of what should actually be yellow / green repeater signals that have a red aspect but are marked as signal XXX not approachable at Red.

 

Basically in normal working situations (Down the Down and Up the Up) the wrong road signal will show a red aspect (done so as to prevent a driver making a mistaking it for the right direction signal they should be obeying and rear ending the train in front are). However once bi-directional working is enabled then the signalling system will treat the wrong road signal as an ordinary yellow / green repeater and not let any train approch it unless it is showing the said yellow or green aspects.

 

It doesn't help that most signal heads or of the twin LED style thus making the diagrams harder to read.

 

 

post-658-0-10288500-1513297906_thumb.jpg

Edited by phil-b259
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When the Paisley/Ayr line was resignalled in the 1980s for electrification, bi-directional signalling was provided between Elderslie and Kilwinning, however similar to the example phil-b259 mentions above, signalling was only provided to enable one train at a time on the 'wrong' line between crossovers. Whenever we had an incident blocking one line and had to use the bi-di, the maximum passenger service possible was half-hourly each way, whereas the booked service then was four per hour, and is now six. And the only way to get a freight through was to reduce the passenger service even further, although this is no longer a major issue since the closure of Longannet Power Station and then end of traffic to and from Hunterston. In contrast, when the additional line was installed between Shields Jc and Paisley (for the cancelled Glasgow Airport link), full signalling was provided on all three lines in both directions. 

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The ECML has quite extensive SIMBIDS working, Northallerton to Low Fell, and Benton Jn to Tweedmouth (the bit in between, roughly 5 mile either side of Newcastle, and Tweedmouth - Berwick are fully Bi-Directional).

As stated, it's only intended for emergency purposes, such as getting round an obstruction, failed train, track defect etc., where Pilotman's working would otherwise be necessary, not normal traffic purposes. As such, although it's more restrictive of capacity than normal signalling (besides the fact when in use you're only using a single line to start with), it's still much better than the alternative.

There's usually just one intermediate stop signal in each section between crossovers, usually 2 aspect, and a Y/G repeater, both sited opposite the corresponding right-direction signals. On some stretches, particularly the 'North' road, there are more intermediate Bi-Di signals where there's level crossings etc to protect, to the point some sections are vitually 3 aspect. The signals that can put you back onto the right line are always at least 3-aspect as this is putting you back to normal signalling and signal spacing.

One point not mentioned previously, SIMBIDS signals are not provided with AWS equipment, though the AWS for the correct direction signals aren't suppressed for wrong direction movements so have to be canceled on passing over each one.

Although full Bi-Di can be anything up to full linespeed, the maximum for SIMBIDS working's 50mph

 

The two systems can even be mixed - Cockburnspath Bank, between Dunbar and Berwick's equipped with Bi-Di working between Innerwick and Grantshouse, however, while the Up direction (also uphill) has full bi-di over the Down, allowing uphill freights to be routed bi-di to be overtaken, and signals opposite each right direction signal, full AWS etc., the Down direction only has SIMBIDS over the Up

Edited by Ken.W
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The bi-di between shrewsbury and nantwich is the latest hi-tech set up, obstacle detector crossings, computer control etc the only thing is to get on to it from the shrewsbury end you need a pilotman to get you out of the station to the first signal!

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The ECML has quite extensive SIMBIDS working, Northallerton to Low Fell, and Benton Jn to Tweedmouth (the bit in between, roughly 5 mile either side of Newcastle, and Tweedmouth - Berwick are fully Bi-Directional).

As stated, it's only intended for emergency purposes, such as getting round an obstruction, failed train, track defect etc., where Pilotman's working would otherwise be necessary, not normal traffic purposes. As such, although it's more restrictive of capacity than normal signalling (besides the fact when in use you're only using a single line to start with), it's still much better than the alternative.

There's usually just one intermediate stop signal in each section between crossovers, usually 2 aspect, and a Y/G repeater, both sited opposite the corresponding right-direction signals. On some stretches, particularly the 'North' road, there are more intermediate Bi-Di signals where there's level crossings etc to protect, to the point some sections are vitually 3 aspect. The signals that can put you back onto the right line are always at least 3-aspect as this is putting you back to normal signalling and signal spacing.

One point not mentioned previously, SIMBIDS signals are not provided with AWS equipment, though the AWS for the correct direction signals aren't suppressed for wrong direction movements so have to be canceled on passing over each one.

Although full Bi-Di can be anything up to full linespeed, the maximum for SIMBIDS working's 50mph

 

The two systems can even be mixed - Cockburnspath Bank, between Dunbar and Berwick's equipped with Bi-Di working between Innerwick and Grantshouse, however, while the Up direction (also uphill) has full bi-di over the Down, allowing uphill freights to be routed bi-di to be overtaken, and signals opposite each right direction signal, full AWS etc., the Down direction only has SIMBIDS over the Up

 

i have always felt that that the signalling at Grantshouse loops is a bit over the top, with all four tracks (two main and two passenger loops) bi-directional.

 

Jim

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The two systems can even be mixed - Cockburnspath Bank, between Dunbar and Berwick's equipped with Bi-Di working between Innerwick and Grantshouse, however, while the Up direction (also uphill) has full bi-di over the Down, allowing uphill freights to be routed bi-di to be overtaken, and signals opposite each right direction signal, full AWS etc., the Down direction only has SIMBIDS over the Up

 

I recall one occasion when two Up freights left Millerhill for the ECML in quick succession; For operational reasons the Operator wanted their order reversed, so the first train ran via Simbids over the Down from Innerwick to Grantshouse, allowing the second train to overtake (there wasn't much other traffic about at the time !)

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Definitely a modern thing in the main, the MML section I mentioned earlier didn't exist until the mid to late '80s.The section between Rugby and Nuneaton has been around for years but the newer bi-di section north of there wasn't commissioned until the about ten years ago.The first time I had to go bi-di to Lichfield it was was quite an eye opener!

Edited by Rugd1022
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