Permissive working through temp single sections?

[biggus]

To minimise bustitution, is it ever safe and practical for trains to run through temp single sections "nose to tail" like motorists passing temp traffic lights?

Clearly sections either side of the single bit would need to be specially controlled for trains to be queued and cleared away, and speed through all 3 sections would be very low, but are there cases where its worth it?

Thanks

 

[Tomnick]

No, some form of block working must be maintained over the single line during SLW - usually normal signalling in the right direction, and either one long section in the wrong direction or divided by Handsignalmen or at intermediate signal boxes (into two sections only on TCB, or as many as there are open intermediate signal boxes on an AB line).

Edit: Just to clarify, dividing the single line as above does mean that trains can be 'flighted' in both directions to make better use of the single line, the Pilotman travelling with the last train in each direction. The use of ABR 3.5 (warning acceptance) is also permitted on an AB line to allow trains to be accepted to approach the single line even where the crossover being used to cross something else over is within the clearing point, making it easier to 'stack' trains.

 

[biggus]

Thanks Tom for an interesting and knowledgeable reply. I dont know owt about signalling so forgive me if you have already covered this above... Do you mean 1) Train spacing is never controlled by the drivers eye in this scenario, but instead 2) relays of handsignalmen may create a series of small blocks through which closely spaced trains may be passed from block to block?

How small can the headway be made assuming very restricted speed?

 

[Tomnick]

No problem, happy to help!

Do you mean 1) Train spacing is never controlled by the drivers eye in this scenario...

Correct - on running lines, there are only a few occasions when you can have more than one train in a section (permissive working, assisting a failure, shunting etc.).

...but instead 2) relays of handsignalmen may create a series of small blocks through which closely spaced trains may be passed from block to block?

Not quite. In the wrong direction, the single line can be divided into shorter sections. On a Track Circuit Block line, this can be done once (with a Handsignalman) if the SB Special Instructions allow it, and the Signalman will communicate with the Handsignalman to ensure that there's only ever one in a section. On an Absolute Block line, it can be divided at each intermediate signal box that's open, and the Signalman at each will give a yellow handsignal to each movement in the wrong direction.

How small can the headway be made assuming very restricted speed?

Speed makes no difference - the section can only be divided as outlined above.

 

[biggus]

Makes sense. Thanks!

 

[Shimbleshanks]

Changing the subject slightly, how common are permanent Permissive Block sections on the national network? I know of one, on the northbound slow line approach to East Croydon. I guess there must be quite strict criteria and circumstances governing their use.

 

[pendolino]

Changing the subject slightly, how common are permanent Permissive Block sections on the national network? I know of one, on the northbound slow line approach to East Croydon. I guess there must be quite strict criteria and circumstances governing their use.

There are quite a few places - like East Croydon (I'm assuming you're thinking of the position light on the signal protecting platform 4 in the up direction - where permissive working is allowed for attaching/detaching. Termini are the obvious places - Victoria, London Bridge, Tattenham Corner, East Grinstead all spring to mind - but also Purley, Haywards Heath for example where trains are booked to attach/detach mid-journey.

 

[Tomnick]

Changing the subject slightly, how common are permanent Permissive Block sections on the national network? I know of one, on the northbound slow line approach to East Croydon. I guess there must be quite strict criteria and circumstances governing their use.

There are three 'types' of permissive working shown in the Rule Book (other than emergency permissive working on a TCB line) - from Module TS2:

3.3.2 Types of permissive working
You must only allow the following classes of train to enter a section when permissive working is taking place:

Type of line    Classes of train
Goods           3 to 8 and 0
Passenger       3 to 8 and 0
(other than platform lines)
Platform lines  1, 2, 3 ECS, 5, 9 and 0

The last must be the most common, as pendolino suggests - at quite a few stations around the country. There are a fair few examples of the first one too, including until recently some quite long stretches of line (complete with auto signals with subsidiary signals!) in the area worked by Trent PSB. Derby might still have some, but I'm not sure. I don't know if I can think of any examples of the middle one though - permissive working for freight trains only, but not on a goods line.

 

[Dieseldriver]

An example that springs to mind which I think the middle one would refer to is Southampton Central up and down loops?

 

[Crossover]

I believe the latter may be applicable at Stafford. Pretty sure some of their platforms allow permissive working (though I have never seen it taken advantage of if so)

 

[Tomnick]

An example that springs to mind which I think the middle one would refer to is Southampton Central up and down loops?

I'm not sure! The Sectional Appendix seems to remain silent on permissive working other than in platforms, so presumably it's not something that Drivers would need to be aware of beyond taking the sub (or not, in the case of a passenger train!) when it comes off?