Bi-Directional Signaling

One use case for bi-directional operation outside of emergencies is having reversible tracks on 3+ track lines to handle peak traffic flows. For example a 4 track line can be run as 3+1 with three tracks in the peak direction at peak times. With highly unbalanced flows they can save the expense of building an additional track. The New York City Subway was big into three track elevated lines with reversible center tracks and don't forget the Chicago Racetrack.

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However, don't underestimate the penny-pinching and short sighted nature of our politicians. If they can see a way to trim the budget by a few million, they often will do, and I wouldn't be surprised if bi-directional signalling has been removed from schemes in the past to keep costs down. I'm not saying it's a good reason not to install it, but it's a reason nonetheless.

That is one of the drawbacks to having an independent operator in charge of the infrastructure. The cost of service disruptions falls to the train operating companies (and/or their passengers). In the United States where the operators own the tracks, bi-directional signaling is always implemented as soon as the money becomes available because having to employ manual reverse running procedures drives the operations people nuts and also increases the risk of accident.

We don't have hand points on passenger running lines here...

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We don't have hand points on passenger running lines here...

Ground frames protected by signals fill the same role. I've used them on sims. Anyway the example was to illustrate additional costs associated with conversion to bi-directionality. For example adding FPLs and/or additional signal protection to "black lever" trailing point crossovers.

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" said:

We don't have hand points on passenger running lines here...

Ground frames protected by signals fill the same role. I've used them on sims. Anyway the example was to illustrate additional costs associated with conversion to bi-directionality. For example adding FPLs and/or additional signal protection to "black lever" trailing point crossovers.

Except that you can't use the protecting signals, and have to clip and scotch the points and hand signal the train moments across them usually while working single line working on a Saturday night

Except that you can't use the protecting signals, and have to clip and scotch the points and hand signal the train moments across them usually while working single line working on a Saturday night

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Except that you can't use the protecting signals, and have to clip and scotch the points and hand signal the train moments across them usually while working single line working on a Saturday night

That gets back to my original question about single direction signaling not being more aggressively eliminated within the last couple of decades. One of my friends who worked for ScotRail explained that if there were major problems on a line, the service would be suspended and replaced by a bus because SLW was so involved. Is this true?

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Except that you can't use the protecting signals, and have to clip and scotch the points and hand signal the train moments across them usually while working single line working on a Saturday night

That gets back to my original question about single direction signaling not being more aggressively eliminated within the last couple of decades. One of my friends who worked for ScotRail explained that if there were major problems on a line, the service would be suspended and replaced by a bus because SLW was so involved. Is this true?

Yes indeed. Welcome to a world where the network is used so intensively that any ad-hoc single line working (whether bi-directional or with pilot man) could well have huge knock-on effects right to the far end of the network

One of my friends who worked for ScotRail explained that if there were major problems on a line, the service would be suspended and replaced by a bus because SLW was so involved. Is this true?

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Except that you can't use the protecting signals, and have to clip and scotch the points and hand signal the train moments across them usually while working single line working on a Saturday night

That gets back to my original question about single direction signaling not being more aggressively eliminated within the last couple of decades. One of my friends who worked for ScotRail explained that if there were major problems on a line, the service would be suspended and replaced by a bus because SLW was so involved. Is this true?

" said:

" said:

Except that you can't use the protecting signals, and have to clip and scotch the points and hand signal the train moments across them usually while working single line working on a Saturday night

That gets back to my original question about single direction signaling not being more aggressively eliminated within the last couple of decades. One of my friends who worked for ScotRail explained that if there were major problems on a line, the service would be suspended and replaced by a bus because SLW was so involved. Is this true?

I can't see the point of having vast swaths of plain line full bidirectional signalling when your running trains on 4 minute headways, you'll never get the chance to use it. The counter peak flow has just as many trains as the peak flow whether they are passenger services or ECS moves back to depot. Fast trains already overtake slow trains where we have 4 or more track railways and on our 2 track railways fast trains overtake slow trains such places as Haywards Heath.

We are not allowed to use our SIMBIDS to run trains in parallel nor will we be allowed to run our full bidirectional signalling in parallel when it becomes commished in March. Having said that it only has the capacity to run 6tph in the wrong direction against a flow 9tph trying to run in the right direction with a 8min section time not including a staion stop if required. Using SIMBIDS or full BiDi is just a get out of jail card that offers a much reduced capacity.

We use SLW quite alot on Saturdays overnight at various locations between East Croydon and Three Bridges where our 4 track railway is reduced down to one for engineering work. Whether it's worth the companies expense to fully BiDi that length of railway for what is an essentially an hourly service on Saturdays nights will be up to the bean counters when it' becomes our turn to be re-controlled / re-signalled.

I'd say one of the main reasons why SLW is not used as much as it used to be is because cuts to staffing levels have left the railway running on the bare minimum number of people. This is particularly true of the supervisors and junior management grades in the Operations side of Network Rail, and these are typically the people who would set up and run SLW on the ground. My experience is that there's often only one on call manager for an enormous geographical area, so putting SLW in place means dragging off duty staff in to work on a voluntary basis and this can take hours to arrange.

Also the requirements around staff competency have been tightened up in the recent past in an attempt to save money, meaning fewer 'competent' staff are available (I put 'competent' in quotes because most Operations staff could do it standing on their head but don't have the required certificate to do so). At one time almost any Signaller could act as Pilotman or Handsignaller but now 99% of Signallers have had these competencies removed from their Authority to Work certificates.

We are not allowed to use our SIMBIDS to run trains in parallel nor will we be allowed to run our full bidirectional signalling in parallel when it becomes commished in March. Having said that it only has the capacity to run 6tph in the wrong direction against a flow 9tph trying to run in the right direction with a 8min section time not including a staion stop if required. Using SIMBIDS or full BiDi is just a get out of jail card that offers a much reduced capacity.

On the Sims that aren't some trunk line into a major city terminal (Trent, Bristol and the Scottish Midlands one come to mind) I have never really noticed the sort of frequency that would make reverse signaling impractical outside of peak periods. I would much prefer the option to cross a train over to run reverse around a goods trains as opposed to stuffing the goods train into a siding.

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One use case for bi-directional operation outside of emergencies is having reversible tracks on 3+ track lines to handle peak traffic flows. For example a 4 track line can be run as 3+1 with three tracks in the peak direction at peak times. With highly unbalanced flows they can save the expense of building an additional track.

I can see the potential, however you'll find that in rush hour the lines are busy in both directions- obviously, the number of trains emerging from a terminus has to be balanced by the number going in. If you had a sufficiently high number of "spare" trains you could do as you describe above, but that's not considered economical. Light rail vehicles, as used on subways and tram routes, are generally cheaper than heavy rail trains (as used on all lines SimSig simulates bar Chicago L, Drain and Victoria LUL), so I can see why a subway company might operate like that.

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Not permitted to? Why not?

Because that's what the rule book says... As eluded to twice already it's a get out of difficult situations tool. If you can run trains on the normal line you shouldn't be using the SIMBIDS

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" said:

Not permitted to? Why not?

Because that's what the rule book says... As eluded to twice already it's a get out of difficult situations tool. If you can run trains on the normal line you shouldn't be using the SIMBIDS

(This reply also applies to subsequent posts)

I know, but it was mentioned also that even full BiDis aren't allowed to be used for this purpose. I understand that SIMBIDS have decreased safety features, but the same is not true of full BiDis, as far as I am aware.

There is no general Rule Book prohibition on parallel moves on adjacent bi-directional running lines. In fact when I was a signaller I used to set up parallel moves over a particular section fairly regularly to keep traffic moving when trains were delayed. There may, however, be Signalbox Special Instructions for a particular location which ban parallel movements for specific local reasons.

Has anyone ever suggested doing away with the use of pilotmen and just switching to verbal instructions a la Air Traffic Control? I'm sure deployment of GSM-R could be used to justify an experiment with that method of operation because its...secure or something.

Will ETRMS "solve" the problem? I assume that HS1 is signaled equally in both directions.

One use case for bi-directional operation outside of emergencies is having reversible tracks on 3+ track lines to handle peak traffic flows.

The key idea is that of traffic control. One's interlocking logic is a lot simpler if routes are single direction. The flavors of CTC between US and UK are certainly different since we use so many true automatics,

but in either case there is logic to prevent a signaler from sending two trains towards each other on the same track section so that one will eventually have to back up. Where every signal is controlled and can act like a holdout, the idea of setting traffic flow on a section of track becomes a bit muddy, but one doesn't need to implement the logic that way since there is almost zero need for two trains to approach each other on the same track without some intervening switch or station.

That being said, CTC can be implemented very inexpensively if one is willing to use true automatic signals and put them back to back like this.

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We don't have hand points on passenger running lines here...

Ground frames protected by signals fill the same role. I've used them on sims. Anyway the example was to illustrate additional costs associated with conversion to bi-directionality. For example adding FPLs and/or additional signal protection to "black lever" trailing point crossovers.

I've always wondered why this is not used more often in the UK. Especialy since the goverments wants a 24h/365 days a year railway. you should be able to do this on the midland mainline or ECML for example.