Insch Signalling

[Norther Monkey]

Passing through Insch recently I spotted what looked to me like an something of an anomaly.omission. Being uninformed on these matters I was wondering if anyone could offer an explanation, please forgive any errors in terminology.

On the Inverness bound line (platform 1) there is no 'starting' signal, thus it appears that once a train is signalled into the platform the level crossing needs to be closed to road traffic. It seems to me that this not only means that the level crossing is closed longer than it would otherwise need to be. In addition does this limit the flexibility for holding a train in this platform, should the need arise?

So, why no starting signal on Insch platform 1?

 

[MarkyT]

Passing through Insch recently I spotted what looked to me like an something of an anomaly.omission. Being uninformed on these matters I was wondering if anyone could offer an explanation, please forgive any errors in terminology.

On the Inverness bound line (platform 1) there is no 'starting' signal, thus it appears that once a train is signalled into the platform the level crossing needs to be closed to road traffic. It seems to me that this not only means that the level crossing is closed longer than it would otherwise need to be. In addition does this limit the flexibility for holding a train in this platform, should the need arise?

So, why no starting signal on Insch platform 1?

Something historic? Perhaps designers and fitters simply wanted to limit the scope of the locking alteration required when the line from the east was singled. I guess signal 2 was near the crossing before singling but was moved back to before the single to double turnout when the second track was lifted. Neither the line nor the road is probably busy enough to make the resulting operational restriction much of a problem. The sort of thing that might be sorted out at next resignalling.
http://tillyweb.biz/gallery/ii/inschdiag.jpg

 

[Railsigns]

Perhaps designers and fitters simply wanted to limit the scope of the locking alteration required when the line from the east was singled.

No, because the lever frame was entirely replaced when the line was singled in 1969.

 

[MarkyT]

The mystery deepens...
This OS map from 1900 shows a down starter (marked S.P) at the immediate west end of the platform:
http://maps.nls.uk//view/82859610#zoom=6&lat=5334&lon=8393&layers=BT
There's also a down home which looks like it is overlap clear of the down siding connection, so it looks like a conscious decision was made in the 1969 works to remove the platform starter.

 

[alxndr]

Unless I'm misunderstood this isn't unique to Insch, I can think of similar situations at Hungerford, Kintbury, and I believe Saxmundham.

 

[MarkyT]

Unless I'm misunderstood this isn't unique to Insch, I can think of similar situations at Hungerford, Kintbury, and I believe Saxmundham.

In continuous colour light signalled areas, as at Hungerford and Kintbury, there are signal spacing constraint that might be part of the reasoning. Unlike semaphore layouts, where you don't need to ensure braking distance between each and every stop signal within the station yard, with colour lights every signal must be placed carefully taking into account braking distance and the correct aspect sequence. Hence designing a layout that caters perfectly for every scenario can be more difficult and compromises must be made. In more rural areas there is also a desire to minimise the number of signals provided as well as control the risk to road users from signal overruns. In those cases, signals have sometimes been placed overlap clearance from the crossing which locates them on the run to the platform, forcing the crossing to be closed before clearance into the platform. As the OP pointed out, there are drawbacks to this design, especially in failure scenarios.

 

[tsr]

There was an incident last summer where a road vehicle destroyed the level crossing barriers at Hungerford. Several trains were required to run at caution and be prepared to stop short of any obstruction. Of course, with a platform between the protecting signal and the level crossing, HSTs were slowing to a crawl adjacent to the station, and were liable to the guard suddenly needing to be ready to perform a train safety check if the train were to stop, given the rules for slamdoor stock.

Therefore, each driver was attempting to drive slowly enough to see if anything was obstructing their progress on the crossing, but fast enough that the train didn’t need to be randomly dispatched at a comparatively small and random station. From what I heard, they were not amused. It must have been a bit distracting!

This sort of signal design has plenty of unexpected consequences.

 

[Norther Monkey]

Thanks for the replies, to me - as a none expert - it still strikes me as odd. The fact that this layout negates the risk of trains over running a stop signal adjacent to an open level crossing makes some sense. Although am I not right in thinking that many locations have stop signals fairly close to level crossings?

 

[47271]

I'm not sure if this is relevant but also bear in mind that the line wasn't ever singled on the Inverness side of Insch, there's a short section of double running from there to Kennethmont. So if the down starter was removed it probably wasn't a direct outcome of singling of the route generally.

 

[MarkyT]

A likely answer at Insch is they moved the block starter forward, so standage in the first signal section on the double line, clear of the single line, is sufficient to hold the longest trains. Having a short section there is operationally risky. The double track AB section ahead is about 5 miles long and there's a single line ahead of that, so it's very plausible that line clear may not be available immediately when a train leaves the single line at Insch onto the long 'dynamic loop'. With the single to double turnout where it is today and a notional platform starter in the traditional position, standage clear of the single line would be under 200m. Anything longer than that, stuck at the signal, would snake back through the turnout and continue to block the single line to movements waiting in the opposite direction. The next signal is actually a little more than 400m further west, so non-stop trains of length no more than this can be relied upon to run straight through the platform and quickly clear the crossing. Stopping at the platform by short trains should normally be a brief affair, so crossing closure throughout and during the preceding run-in, is not excessive.

 

[Norther Monkey]

Again, thank you, that makes sense Marky, although it still seems a little limiting not having an intermediate signal prior to the level crossing I guess for current usage the system works.

Out of curiosity though, if an Inverness bound train failed in the platform how easy would it be to reopen the level crossing?