Curious workings between Bristol & Bath

[whole diary]

[John R]

Trains were running wrong line in both directions between Temple Meads and Bath this morning. (Was on the 0800 ex Bristol, and saw two trains heading the opposite direction.) I can understand why wong line working on one line would be used, but both??

I see that signalling problems are mentioned on FGW^▸ (First Great Western)'s site, so I can only presume that one of the lines can be used "wrong direction" but not in the normal direction, and the decision was taken to try and maintain the service by switching lines.
 

[tramway]

Now 9.16 and sat wrong line just outside Bath on the 08.23 ex TRO^» (Trowbridge - next trains). Interesting morning.

Just wondering if we'll be AXED at Bristol. 

Edit at 09.25, we've been Axed.

[eightf48544]

Aren't the lines between Bristol and Bath bi-directionally signalled? In which case wrong line running is actually a signalled move and the driver should obey the relevant signals. Not sure how long the sections are and where the crossovers are situated.

Although it reduces capacity it useful for overtaking failed trails etc.

[John R]

Aren't the lines between Bristol and Bath bi-directionally signalled? In which case wrong line running is actually a signalled move and the driver should obey the relevant signals. Not sure how long the sections are and where the crossovers are situated.

Although it reduces capacity it useful for overtaking failed trails etc.

Yes they are both bi-directional and so fully signalled, but I've never experienced both lines being used "wrong line" at the same time. There are no crossovers between Bristol and Bath (or at least they weren't being used.)   

[Southern Stag]

The signalling sections when running wrong line are much longer as well so combined with having to cross over at either end the capacity of the line would have been reduced quite significantly. The problem was that it one direction the signalling system thought it being run reversibly, so it would not allow trains to be signalled in the normal direction along the line. Whilst the fault was investigated the solution was just to run in the wrong direction on both lines.

[John R]

That's helpful. Thanks for the explanation Southern Stag.

Out of interest - I did notice that the majority of the signals on the up line (ie the one we should have been using) were green in the up direction, and only turned to yellow and red as we neared the oncoming down train. This surprised me, as I would have expected if a line is being used in one direction then all the signals in the other direction would be at danger.   

[SandTEngineer]

This type of signalling is called SIMBIDS (SIMplified BI Directional Signalling).  This allows for wrong direction running between crossovers but (usually, but not always) without intermediate signals for the wrong direction.  To allow SIMBIDS to be installed on existing lines it was designed as an overlay to the existing system so to keep costs down no controls were placed into existing intermediate right direction signals hence aspects step down (i.e. go from G-YY-Y-R) when a train is coming the wrong way.

[John R]

Yes, that's what I saw. (Though there are quite a few intermediate signals running wrong line, in this case.)

Presumably there has to be some sort of control that prevents any trains from entering the line from both directions, as the normal signal distances would be inadequate if a train is approaching you from the opposite direction and stepping down signals as it comes (so you could go straight from a green to a red with 3 aspect signalling)?

Finally, I noticed that we slowed quite markedly when passing through Keynsham. This could have been as the train had been checked, but I did wonder whether it's to prevent the surprise factor of a train running wrong line through the platform at high speed.

[SandTEngineer]

Some of the longer SIMBIDS sections are divided by intermediate signals.  Here is a link to show a typical SIMBIDS section http://www.s-r-s.org.uk/archivesignals/brwr/1981-31w2769.pdf (diagram at the end)
This may be a bit technical for your average reader but if there is anything you need to understand them I'm here

[SandTEngineer]

Presumably there has to be some sort of control that prevents any trains from entering the line from both directions, as the normal signal distances would be inadequate if a train is approaching you from the opposite direction and stepping down signals as it comes (so you could go straight from a green to a red with 3 aspect signalling)?

The interlockings sited at each end of the SIMBIDS section establish the direction of running for each section between them (so setting them to either UP or DOWN direction running on each line).  To change the direction requires the whole section on that line to be clear of trains.  If there are intermediate signals then trains can follow in the established direction only.

[John R]

Great. Thanks for the info. There were at least two down trains on the up line this morning, and a third waiting to leave Bath once we had crossed back over, so the intermediate signals were being well used.

[Southern Stag]

Presumably there has to be some sort of control that prevents any trains from entering the line from both directions, as the normal signal distances would be inadequate if a train is approaching you from the opposite direction and stepping down signals as it comes (so you could go straight from a green to a red with 3 aspect signalling)?

The interlockings sited at each end of the SIMBIDS section establish the direction of running for each section between them (so setting them to either UP or DOWN direction running on each line).  To change the direction requires the whole section on that line to be clear of trains.  If there are intermediate signals then trains can follow in the established direction only.

As far as I can tell that is what failed this morning as well. One of the lines was incorrectly stuck in wrong direction running.

[WelshBluebird]

Out of curiosity how would this have affected the stopping services (stops at Keynsham and Oldfield Park).
I doubt anyone at those stations would have known until they saw trains on the other side.
So could have caused a fair amount of delays with people changing to the other platform.
Or are there crossovers before and after the stations so the trains could run "wrong line" between the stations but then move onto the correct line for the stops?

[SandTEngineer]

In the case of Bristol to Bath the crossovers are at Bristol East Depot and Bath West.  I guess the wrong direction working at stations would be covered by PA^▸ (Public Address) Anouncements?

[Louis94]

In the case of Bristol to Bath the crossovers are at Bristol East Depot and Bath West.  I guess the wrong direction working at stations would be covered by PA^▸ (Public Address) Anouncements?

No PA at Oldfield Park or Keynsham.