Kemble, Lack of Trap Point

[Rods_of_Revolution]

I was at Kemble a few weeks ago and noticed that the loop has no trap point. I was wondering why this was, if an up train was sliding out of control it would surely push through the point (if it was even set against it) which goes to the Tamper Siding and be directed into the path of a train coming down from Swindon?

 

Here is a picture I took showing the southern end of the loop,

 

 

Kindest Regards,

 

Jack

[beast66606]

No need as the protecting signal is at least 200 yards from the fouling point.

[Rods_of_Revolution]

I'm surprised, I could understand that on a siding or loop but where two main running lines converge I'd have thought they'd have just implemented a trap to be on the safe side, it can't be much more than 200 yards from the signal, certainly less than 300 yards. Trains slide well over 200 yards in the right circumstances; I've read about Turbos sliding over a mile.

 

It's even more risky due to the fact that passenger trains are booked to stop in Kemble station just prior to the down service from Swindon arriving to minimise waiting times, so if an up train did slide the 250yrds to the point then it would almost certainly collide head on with the down service.

 

Regards,

 

Jack

[beast66606]

The railways set a limit for an overlap, 440yds for semaphore and 200yards for colour light (other permutations but these will suffice), if everything had to be trapped because of a slide through risk then there would be huge numbers of trap points, especially on single lines or junctions, if the protecting signal is at the overlap or greater than trapping is not (normally) necessary, it makes no odds if it's 200.00001 yds or 299 yds or ...

[Absolute Aspects]

Trap points used to be a lot more frequent, but with advance in systems like TPWS plus the point that beast has made they look as if they are slowly being phased out.

 

Matt

[The Stationmaster]

I see my original comment has vanished, no doubt due to the server problems. Beast has made the critical point in respect of Kemble that there is a suitable overlap distance (a quick check indicates that it is 328 yards from the toe of the double to single connection to the protecting signal on the Up Line so it is indeed an adequate overlap).

 

A further point is that by the time the line was singled, in mid 1968, it was already long decided to avoid trap points wherever possible on passenger lines and even under 'the Requirements' (as they had been for some considerable time prior to then) trap points were not required in such circumstances at double to single line connections (because they are far more trouble than they are worth). As Beast said back in December you then begin to look at everywhere there are such circumstances and the perceived 'need' for a trap point turns into ludicrous numbers which clearly made little sense on even the mid-20th century railway let alone one with the benefit of AWS and TPWS.

 

Finally it might be worth noting that this situation has existed at Kemble for the best part of 43 years.

[RIP OO]

Trap points used to be a lot more frequent, but with advance in systems like TPWS plus the point that beast has made they look as if they are slowly being phased out.

 

Matt

....because the days of unfitted goods trains are in the past...

[Edwin_m]

You're thinking of catch points, which are used to derail a train breaking away and rolling back down a hill. This discussion is about trap points, used (sometimes) to derail a train that goes through a signal at a danger.

[RIP OO]

You're thinking of catch points, which are used to derail a train breaking away and rolling back down a hill. This discussion is about trap points, used (sometimes) to derail a train that goes through a signal at a danger.

I was thinking of unfitted goods not pulling up in the right place but hey - have it your way.

[beast66606]

I was thinking of unfitted goods not pulling up in the right place but hey - have it your way.

 

So your thinking was wrong, but hey, have it your way.

 

You could always try reading the thread and stop assuming we don't understand what we are talking about.

[RIP OO]

So your thinking was wrong, but hey, have it your way.

 

You could always try reading the thread and stop assuming we don't understand what we are talking about.

We being...?

[beast66606]

Those of us who read threads and think before posting - we have other attributes but those two are the important ones.

[Donw]

Is there not a distinction between running lines where the train is considered to be in control and sidings where shunting vehicles could be moving with little control? Traps seem to make more sense when a rough shunt could result in a wagon fouling the main.

Don

[JZ]

It's even more risky due to the fact that passenger trains are booked to stop in Kemble station just prior to the down service from Swindon arriving to minimise waiting times, so if an up train did slide the 250yrds to the point then it would almost certainly collide head on with the down service.

 

Jack

 

I regularly work this line and trains, when running on time, pass between Sapperton tunnel and Stroud. They are booked to leave both Swindon and Gloucester at the same time.

[The Stationmaster]

Is there not a distinction between running lines where the train is considered to be in control and sidings where shunting vehicles could be moving with little control? Traps seem to make more sense when a rough shunt could result in a wagon fouling the main.

Don

Yes - sidings have to be trapped (or have a wheel scotch where a trap can't be fitted and the risk is considered less).

[phil-b259]

In P-yay and signalling terms, pointwork is more expensive than plain line and as a result the provision of trap points at the end of loops on running lines was judged a needless expense, providing the standard overlap could be provided with colour light signaling and AWS providing further protection.

 

While this is all very well in theory, as the head on accident at Cowden in the 90s proved the aforementioned setup is far from watertight and if a driver SPADs a signal there is nothing to prevent an acident from ocuring (On the Uckfield line the signals giving entry to the single line sections had their overlaps doubled to 400 yards because of concerns about SPADs).

 

Since then however the introduction of TPWS (and a network wide ban on the movement of unfitted trains) has finally removed this possability, effectivley taking the place of trap points meaning that from a saftey perspective the layout at Kemble pressents no risk at all. (From the photo the tamper siding visable under the bridge looks to have a trap point provided protecting the passenger lines from runways

[Edwin_m]

As far as I know the abolition of unfitted trains hasn't changed the rules on either overlap length or the provision or otherwise of trap points. This set me wondering whether trains running through traps due to lack of brake force, with no descending gradient involved, was ever a signficant safey risk.

 

There have been plenty of occasions where unfitted or partly-fitted trains have run out of control on steep down gradients, but can anyone think of one where such a train has run out of control on level, ascending or moderate descending gradients and resulted in any significant consequences? I'm thinking of situations where the driver knew he needed to stop but couldn't, not where the driver missed or ignored the signal.

[The Stationmaster]

As far as I know the abolition of unfitted trains hasn't changed the rules on either overlap length or the provision or otherwise of trap points. This set me wondering whether trains running through traps due to lack of brake force, with no descending gradient involved, was ever a signficant safey risk.

 

There have been plenty of occasions where unfitted or partly-fitted trains have run out of control on steep down gradients, but can anyone think of one where such a train has run out of control on level, ascending or moderate descending gradients and resulted in any significant consequences? I'm thinking of situations where the driver knew he needed to stop but couldn't, not where the driver missed or ignored the signal.

 

I think we need to separate other thing out as well on this issue. Firstly trapping of single line crossing places - which Kemble could in some respects be seen as - was unusual in other than 'special circumstances' long before there was a double to single connection at Kemble. Secondly thtrapping of passenger loops was also more or less a thing of the past by the time thls section was singled and within a few years was very definitely a thing of the past - trap points at loops were responsible for more passenger train derailments than almost any other factor in the elate 1960s/early '70s and very few of those derailments involved SPADs. And of course we come back as well to the original answer regarding overlaps so effectively there were two very good reasons and one increasingly regarded as good reason for not providing a trap at Kemble when the line was singled.

 

As far as run throughs by unfitted etc freights are concerned I think you could probably count on the fingers of one hand. I spent several years working in South Wales - where they had some real gradients and I'm aware of only three run throughs on trap points by freights in that period and one of then involved a fully fitted train (Driver error on steep gradient), one involved a partially fitted train leaving a yard - and the train was under power when it derailed due, again, to Driver error which also included a SPAD and the third was back in England on a goods loop on level line and was entirely down to mishandling of a partly fitted train and it was only stopped by demolishing a building containing a large quantity of cable joints and a few relays.

 

On a railway running hundreds of trains a week (in fact probably over 1,000 per week back then) that was a pretty low likelihood and none of them involved an unfitted train pushing the loco.

[Edwin_m]

Thanks Mike, that tends to confirm my suspicion that the presence of partly fitted or unfitted freights is not and never has been a reason to use trap points. Unless anyone else knows different?