Trap / Catch Points

[spsmiler]

Jun 17, 2016 16:29:12 GMT countryman said:

An empty train went through a red light 'causing an automatic derailment'(or close to that). What it really means is that the catch point did its job.

Yes but in light of what happened when the catch point did its job, perhaps the positioning of catch points and where the likely path followed by the derailed trains should be reviewed, with some of the catch points possibly being moved to locations where the derailed trains are less likely to end up impacting signals or overhead wire supports.

Simon

[Chris M]

Jun 17, 2016 21:33:45 GMT spsmiler said:

Yes but in light of what happened when the catch point did its job, perhaps the positioning of catch points and where the likely path followed by the derailed trains should be reviewed, with some of the catch points possibly being moved to locations where the derailed trains are less likely to end up impacting signals or overhead wire supports.

Simon

Yes, either that or relocate the infrastructure a derailed train would hit. After all, if a gantry or other structure* spanning other lines is brought down then it could become foul of gauge and be impacted by other trains with significant consequences.

*At Castle Cary there are trap points that would derail directly into the passenger footbridge support.

(click for other sizes and full details)

[MoreToJack]

Jun 17, 2016 23:54:51 GMT Chris M said:

Jun 17, 2016 21:33:45 GMT spsmiler said:

Yes but in light of what happened when the catch point did its job, perhaps the positioning of catch points and where the likely path followed by the derailed trains should be reviewed, with some of the catch points possibly being moved to locations where the derailed trains are less likely to end up impacting signals or overhead wire supports.

Simon

Yes, either that or relocate the infrastructure a derailed train would hit. After all, if a gantry or other structure* spanning other lines is brought down then it could become foul of gauge and be impacted by other trains with significant consequences.

*At Castle Cary there are trap points that would derail directly into the passenger footbridge support.

(click for other sizes and full details)

In many cases it comes down to the 'least-worst' option. Ultimately three days of disruption whilst an OHLE mast is replaced and the knitting reconnected is a better outcome than a serious head-on collision. Neither is ideal, of course.

There are several instances of trap points that lead directly over the end of embankments or bridges and onto roads, fields or even canals. 

[Jerome H]

There are also many ways to protect the OLHE equipment, however there is a strong ethical arguement whether you protect the equipment or you protect the train

[crusty54]

Jun 18, 2016 16:58:33 GMT Jerome H said:

There are also many ways to protect the OLHE equipment, however there is a strong ethical arguement whether you protect the equipment or you protect the train

the question is why put any supports in the catch points alignment?

Should a 25,000 volts cable drop onto a train before the circuit trips you could have serious problems.

[tunnelbore]

Jun 18, 2016 17:10:11 GMT crusty54 said:

Should a 25,000 volts cable drop onto a train before the circuit trips you could have serious problems.

25kV cable dropping on to the train will be earthed by the train and the circuit breakers will one very quickly, probably in less than 0.25s. The coach body may rise in potential a bit but people inside will be safe because of the Faraday-cage formed by the coach body (which keeps the charge on the outside surface).

This report on the incident at Walkergate was alarming for what is shows about the arcing and fire risk when the fault current / protection settings are not well configured and the breakers aren't opened.

 

[rincew1nd]

Thinking about he location of catch points, there was an RAIB report into a freight runaway in Scotland one winter which ended up with the loco taking a plunge down an embankment. Whilst it was noted, I think this was preferred to the alternative of it ploughing into a platform full of people.

Edit to add link to report www.raib.gov.uk/cms_resources.cfm?file=/110224_R032011_Carrbridge.pdf

[Deleted]

At the same time, wheel stops are, I believe, used at the exits of the Battersea Pier sidings, just outside London Victoria station, due to the fact that catch points would send a train into the Thames.

[spsmiler]

I am amazed by the photograph of catch points leading to the footbridge support.

Its totally stunning.... for all the talk I've seen over the years about the "safety first" culture of the railways, especially with respect of "fail to safe" signalling and the perceived benefits of aircraft style black box surveillance systems in case a train should travel a few mph about the line speed limit, I find it hard to understand how the simplest most obvious dangers (as illustrated on this page) can be accepted as safe. Especially when its in a rural area where there are nearby fields to which a derailed train could be directed.

Simon

[bassmike]

Brings to mind several locations (although like remembering jokes when you want to ) I can't name one , where trap points direct straight into the bases. of signal boxes. Might be/have been one at Canonbury but probably wrong.

[Deleted]

Jun 18, 2016 12:48:17 GMT MoreToJack said:

Jun 17, 2016 23:54:51 GMT Chris M said:

Yes, either that or relocate the infrastructure a derailed train would hit. After all, if a gantry or other structure* spanning other lines is brought down then it could become foul of gauge and be impacted by other trains with significant consequences.

*At Castle Cary there are trap points that would derail directly into the passenger footbridge support.

(click for other sizes and full details)

In many cases it comes down to the 'least-worst' option. Ultimately three days of disruption whilst an OHLE mast is replaced and the knitting reconnected is a better outcome than a serious head-on collision. Neither is ideal, of course.

There are several instances of trap points that lead directly over the end of embankments or bridges and onto roads, fields or even canals. 

This must surely form an HSE investigation???

[superteacher]

You'd think they might provide some form of arresting device to slow the train down?

[roythebus]

Yes, like brakes?

[Tom]

Jun 19, 2016 20:32:37 GMT spsmiler said:

I am amazed by the photograph of catch points leading to the footbridge support.

Its totally stunning.... for all the talk I've seen over the years about the "safety first" culture of the railways, especially with respect of "fail to safe" signalling and the perceived benefits of aircraft style black box surveillance systems in case a train should travel a few mph about the line speed limit, I find it hard to understand how the simplest most obvious dangers (as illustrated on this page) can be accepted as safe. Especially when its in a rural area where there are nearby fields to which a derailed train could be directed.

Simon

The things that would be considered are:
Likelihood of someone being on the footbridge x Likelihood of a train being in the siding x Likelihood of that train then having a SPAD x Likelihood of the train not stopping more or less instantly. When you do the maths in a risk assessment the figures you get would easily fall into the broadly acceptable region.

Oh, and folks: On a technicality, these are Trap points - they're powered and trap trains in a siding. Catch points are unpowered and used to catch (derail) unfitted wagons running wrong line down a hill.

[Chris M]

Wouldn't the consequences of any collision with the footbridge have to be factored in to the risk assessment as well?

[Deleted]

Jun 21, 2016 0:28:42 GMT Chris M said:

Wouldn't the consequences of any collision with the footbridge have to be factored in to the risk assessment as well?

Surely they are when the likelihood of someone being on the footbridge is factored in.

If nobody's on the footbridge, then the consequences of a train colliding with it are extremely minor from a health and safety perspective. I suppose hitting the bridge is more of a danger to the driver than rolling into the field. But from an extremely crude analysis (involving someone as uninformed as me briefly staring at a picture and nothing more), it doesn't look like hitting the bridge would be likely to cause much injury.

Although I suppose you are right, a distinctly less crude analysis of the risk to the driver from hitting the footbridge might well deserve to be factored in to the risk assessment.

[Chris M]

Don't forget also that if the footbridge is damaged by being hit by a train (very likely I think) it could foul other lines with obvious risks to passing trains.

It seems like the footbridge is downhill of the sidings, so a runaway is possible. No injury to the driver is likely in that scenario but it would likely be longer before trains were stopped on other lines pending checking the gauge hasn't been compromised.

[Deleted]

That's actually a very fair point.

The bridge does look relatively insubstantial and I would expect most trains come off significantly better than the footbridge in that particular battle. In other words, if it does foul other lines, I wouldn't expect much harm to come to anybody on board any train that were to hit it.

However, I'm perfectly convinced that that risk should be explored and included in the assessment you're right.

A career in health and safety is apparently not my calling

[tjw]

A first look suggests this does not look safe, but I notice the rusty rails and the state of the track beyond. I also note that the catch point has a ground signal (low speed movements)

So I have had a look at the track plan from bing maps, birds eye view...
1. The foot bridge is linking a foot path to the station platforms, this foot path is across fields... so hardly Claphan Junction numbers of people.
2. The foot bridge has another support on the island platform before crossing the main line, I suspect an impact will only bring down the span over that single line.
3. The catch point is protecting the loop line from the sidings which are a simple run round loop, what is the speed limit on those sidings? 10 mph, are they Level? perhaps the speed of a train is so low that the train may not get to the bridge support?
4. Are these sidings used for normal timetabled services or are they for engineering works?

I think the risk may be quite small...

[rincew1nd]

Interesting that we are talking about this subject and the RAIB have released a bulletin about a runaway in Bury and the consequences of the trap points.

www.gov.uk/government/publications/bury-safety-digest/runaway-and-derailment-of-a-rail-vehicle-near-bury-greater-manchester-22-march-2016

This accident demonstrates the importance of assessing the risks of using trap points to protect lines and why assessments should include an examination of the potential consequences of derailing, such as the possibility of vehicles fouling running lines or encountering other hazards

[class411]

Jun 21, 2016 0:28:42 GMT Chris M said:

Wouldn't the consequences of any collision with the footbridge have to be factored in to the risk assessment as well?

Certainly.

You multiply the probability of the points being 'used in anger' by the probability of the bridge being occupied at the time.

That will give you your 'bystander' risk, which you would the have to combine with the risks to the driver and the passengers (and guard).

Does anyone know of the stats for:

a) Number of these points extant?
b) Number of times they have been needed?

[norbitonflyer]

The consequences are not just danger to anyone on the bridge, but also to anyone, or anything, under it when it comes down - up to and including a train approaching on the parallel track protected by the trap points.