Block section --- offering forward

[feldom76]

There are several block sections on a straight line. Box 1 offers a train to Box 2 whose section is clear. Can the train be offered to Box 3 and then offered to Box 4 if all sections are clear? Or can it not be offered until it actually enters each section?

Regards Mike

 

[Tomnick]

Unless the special instructions state otherwise (usually where sections are short), ILC shouldn't be sent forward (i.e. B to C) until train entering section is received from the box in rear (i.e. A). Sometimes they do get pushed forward more than they ought to (usually to group bell signals rather than end up back at the bell after half a minute), but this isn't an official practice and needs to be carried out with care (if everyone pushes it on a couple of minutes early, it can end up very early after a few boxes, which can cause problems!).

 

[edwin_m]

As Tomnick mentions, this is necessary where boxes are close together, otherwise there isn't time to complete the offer-accept process and clear the signals in time to give the train a clear run. In the past when there were many boxes in the vicinity of some stations, a train could legitimately be belled several boxes ahead. However most or all of these will either have been re-signalled or rationalised with some boxes closed and control transferred to the remaining ones.

 

[Gwenllian2001]

As Tomnick mentions, this is necessary where boxes are close together, otherwise there isn't time to complete the offer-accept process and clear the signals in time to give the train a clear run. In the past when there were many boxes in the vicinity of some stations, a train could legitimately be belled several boxes ahead. However most or all of these will either have been re-signalled or rationalised with some boxes closed and control transferred to the remaining ones.

I am reminded of the Fifties and Sixties when trains ran at frequent intervals on the Barry line. Cadoxton South was then the 'nerve centre' of the system, passing trains on to the Barry Main Line via Wenvoe; the Line via Cogan and the ex TVR line via Penarth. It was normal practice to 'Ask On' as soon as a train entered the section otherwise everything would have quickly ground to a halt.

 

[Tomnick]

I am reminded of the Fifties and Sixties when trains ran at frequent intervals on the Barry line. Cadoxton South was then the 'nerve centre' of the system, passing trains on to the Barry Main Line via Wenvoe; the Line via Cogan and the ex TVR line via Penarth. It was normal practice to 'Ask On' as soon as a train entered the section otherwise everything would have quickly ground to a halt.

That's the normal practice at the vast majority of boxes though! The exceptions are those where the train needs to be offered forward before 'train entering section' is received (usually either immediately or upon receipt of 1-2-1). Must indeed be a bit of a rarity now though!

 

[JoeGJ1984]

If 1-2-1 (Train Approaching) is authorised, when is it sent to the box in advance?

 

[Tomnick]

That'll be specified in the box special instructions too - in one of the boxes I work, it's sent upon receipt of TES from the box in rear, but at two others it's sent upon occupation of a specified track circuit.

 

[matchmaker]

When the Glasgow-Edinburgh push-pull service was introduced in the early 1970's, there was insufficient in the budget to upgrade much of the signalling, so apart from an NX panel being fitted at Cadder, mechanical signalling and absolute block was retained between Greenhill Upper Junction and Haymarket Central Junction.

The push-pull sets were signalled by the bell code 4-4 and as soon as one was offered from the box in rear it was offered on to the box in advance, so tight were the timings (even today, the best time between the two cities is more than in 1971)

You didn't delay these services if you could, but I do remember being in Bo'ness Junction one summer Saturday when a signalmans error at Polmont meant that a Dunblane - Edinburgh service worked by a Class 101 got ahead of a push-pull.

We had to bring the push-pull almost to a halt at Bo'ness before the 101 got looped at Linlithgow and we managed to pull off the up line signals.

The amount of 6LDA28 thrash was unbelievable!

 

[Tomnick]

How many consecutive boxes passed it forward upon receipt then? Sounds rather like q sledgehammer to crack a nut if each one was pushed forward twenty miles or so with a fairly significant junction in the middle .

 

[matchmaker]

How many consecutive boxes passed it forward upon receipt then? Sounds rather like q sledgehammer to crack a nut if each one was pushed forward twenty miles or so with a fairly significant junction in the middle .

Short(ish) block sections - Polmont to Bo'ness and Bo'ness to Linlithgow were just over 2 miles, for example. Not much for a service timed for 90mph running!

 

[Railsigns]

When the Glasgow-Edinburgh push-pull service was introduced in the early 1970's, there was insufficient in the budget to upgrade much of the signalling, so apart from an NX panel being fitted at Cadder, mechanical signalling and absolute block was retained between Greenhill Upper Junction and Haymarket Central Junction.

Greenhil Upper Junction SB also acquired an NX panel around the same time as Cadder, by the way.

 

[Tomnick]

Short(ish) block sections - Polmont to Bo'ness and Bo'ness to Linlithgow were just over 2 miles, for example. Not much for a service timed for 90mph running!

How long did it take them to pull off?! One of our boxes has to get his barriers down and signals cleared for 90mph trains, after receipt of TES (although at least with authority to offer forward immediately) - and that's a 90mph section, rather less than two miles long!

 

[matchmaker]

Greenhil Upper Junction SB also acquired an NX panel around the same time as Cadder, by the way.

I'm not sure of exact dates, but Greenhill Upper still had a mechanical frame in mid 1971. It did acquire an NX panel housed in the original building but I'm not sure when. The panel later ended up in an extremely ugly single storey building and the original box was demolished.

 

[Railsigns]

I'm not sure of exact dates, but Greenhill Upper still had a mechanical frame in mid 1971. It did acquire an NX panel housed in the original building but I'm not sure when. The panel later ended up in an extremely ugly single storey building and the original box was demolished.

Both Cadder and Greenhill Upper boxes had panels provided in December 1971; Greenhill's panel was brought into use one week before Cadder's. The Greenhill panel was replaced by a new NX panel in the existing relay room building in 1990.

 

[matchmaker]

Both Cadder and Greenhill Upper boxes had panels provided in December 1971; Greenhill's panel was brought into use one week before Cadder's. The Greenhill panel was replaced by a new NX panel in the existing relay room building in 1990.

I was relying on my memory - not a good idea from 42 years ago!

 

[83G/84D]

Newquay branch in Cornwall. When "is line clear.........." is sent for a train from Par to St Blazey for a train for the Newquay branch the "is line clear......." is immediately passed on to Goonbarrow Jn BEFORE "train entering section" is received by St Blazey from Par.

Similar arrangements applied between both the boxes at Newton Abbot & also at Exeter St David's (and plenty of others) not too long ago.

 

[1D53]

It used to happen more before the Irk Valley accident. http://en.m.wikipedia.org/wiki/Irk_Valley_Junction_rail_crash

Nowadays it has to be authorised in the box special instructions.

 

[Tomnick]

The time at which 'is line clear' is normally forwarded (i.e. upon receipt of TES) has been specified in the signalling regs for many years: almost certainly predating the Irk Valley accident. Pushing trains forward by a minute or two was, I'm sure, as unofficial a practice then as it is now - one of the boxes there (Woodlands Road?) was offering them forward long before they were even offered from the box in rear though, and even that was insignificant compared to the other irregularities at some of the boxes on the line (for example: false TRB entries, switching in and out in what soudns like a very dangerous manner and fouling the clearing point with a train accepted under Reg 4).