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Also years ago we did not have a signalling system that dropped at the drop of a hat. Wet or extremely hot weather and the whole system drops.
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How many signalling system collapses have there been in the last 5 years? 10 years?

Alex C

Adelaide does have signal overlaps but their length is quite random and does not appear related to train speed. The signals protecting the approach to Brighton are located some 100s of metres from the facing switches they protect similarly for the down approach to Tonsley Junction. However the up signal protecting the main line at Tonsley Junction is almost on top of the trailing switch it is protecting. There are no overlaps at Showgrounds.

There is some sense in the Yellow signal rule if it is applied sensibly rather than a blanket restriction. I have offered a sensible and low cost fix.

In normal usage the term overlap refers to the arrangement of track circuits in relation to colour light signalling rather the positioning of switches and signals.  Overlap in the effective extension of the track circuit beyond a section into the following section.  A signal can only be cleared for entry into a section provided that both the section and susequent overlap are clear.  Typical overlap length is 100-200m.  The overlap is intended to give a degree of protection in event of a train overrunning a stop signal and there being a second train stopped just into the next section.  Switches may be located within the overlap of a signal, particularly in station approaches, but the preceding signal can only be cleared if a route is clear for the overlap distance.  As you have noted at Brighton the signals protecting a junction may be somewhat further than the overlap distance from the junction.  Signals are primarily positioned to give even section lengths but sighting issues are also a consideration.

From observation on the Seaford line overlaps are typically 150-180 m.  (Here of course the track circuits are now implemented using axle counters.)  Identifying on the ground the track circuits that provide the overlap for signals is not always straightforward, since track circuits serve other purposes, such as locking switches while trains pass, activatiing level crossings and pedestrian gates.  The operation of the overlaps can be seen on straight stretches of line where the signals are set for automatic operation (eg Mile End - Keswick) where you can see signals turning to red when a train passes but returning to yellow quite a few seconds after the following signal goes to red.  Where signals are cleared under manual control it is not possible to observe the effect of overlaps.  

At Showgrounds the overlap extends through the succession of track circuits through the crossovers.  Tonsley Jn is an interesting situation.  Even before the junction remodelling the distance from the Up signal (1034) at Ascot Park was within 75m of the up end of the crossover.  Thus up movements from the branch would foul the overlap on the main line.  I note that prior to last year's the preceding signal (1132) on the Marion Rd overpass was A plated and had both red and yellow as normal aspects.  Last week I observed the operation of 1132 which is normally at yellow but is held at red at the times that Up Tonsley trains would be passing the junction.

Alex C

Alex

Thanks for clearing that up.

Regards
Ian

How many signalling system collapses have there been in the last 5 years? 10 years?

Alex C

The Belair line ground to a halt with signal issues on Friday afternoon, and the previous Wednesday.

Both days were warm, but not extreme weather as they were both well short of 36.8° which is the 95th percentile temperature for Adelaide.

Any slight shower of rain in places takes it out at times also as Justapassenger said a slight warmish day and things start to happen, and then we have to put up with lightning strikes and some of these were not even on the electric system to Seaford but on  the Gawler line or at Adelaide itself so over the previous 5 years I would say there have been plenty of outages, not to mention some that were caused by vandalism either!

Any slight shower of rain in places takes it out at times also as Justapassenger said a slight warmish day and things start to happen, and then we have to put up with lightning strikes and some of these were not even on the electric system to Seaford but on the Gawler line or at Adelaide itself so over the previous 5 years I would say there have been plenty of outages, not to mention some that were caused by vandalism either!

I must do all my rail travel on cool, dry days!  Are there particular locations that are prone to signal failures?  Most of my travel this year has been on the Seaford line. I can see that the Belair line is more prone to disruption with its single line sections.  The effects of lightning and vandalism are difficult to control.  The implication of your original comment was that the signalling was prone to system wide failures and it was that that I was to trying to evaluate.

Alex C

I must do all my rail travel on cool, dry days! Are there particular locations that are prone to signal failures? Most of my travel this year has been on the Seaford line. I can see that the Belair line is more prone to disruption with its single line sections. The effects of lightning and vandalism are difficult to control. The implication of your original comment was that the signalling was prone to system wide failures and it was that that I was to trying to evaluate.

Alex C

Alex

Don't expect facts, only opinion.

Ian

I caught an up Seaford the other day, possibly Wednesday but who could be certain. It was to run express from woodlands or somewhere equally disinteresting and it did, except for the stops for red signals at Goodwood and Showgrounds...

I caught an up Seaford the other day, possibly Wednesday but who could be certain. It was to run express from woodlands or somewhere equally disinteresting and it did, except for the stops for red signals at Goodwood and Showgrounds...

Aaron

What day did you catch it and what day did it arrive at ARS?

The thing is though years back with the old signalling system a fault on one line was confined to that line and did not affect the rest of the system but these days a major fault will usually bring about the whole system failing and nothing moving at all it has happened a few times. If one line is out of action because of a severe signalling fault it does not really matter to anyone else but the passengers on that line or intending passengers. But when a fault brings it all to a stop then everyone suffers, even if it has got nothing to do with your train line at all. It should be able to be made to be slightly separate for each line and only come together at Adelaide station. It was done in the old days with signalling so should still be able to be done now with advances in modern technology. But this is Adelaide and in particular Adelaide Metro we are talking about here! At times I think Murphy was the electrical and signalling engineer that oversee's it all.

I have got to my local station on the Outer Harbor line to be greeted by a person in a Adelaide Metro hi vis vest that tells due to a major problem at Goodwood or somewhere that the trains are not running! It has got bugger all to do with the Outer Harbor line if that is so, but still you are directed to take the bus! I have had it happen twice like that so far and that to me is twice too much.

Why can't they make it so that each line or group of lines runs separately from all others? Here in Melbourne they do and as a result, a fault on one line will only affect the group which that line is in, minimizing the disruption. In fact, in most cases it only affects that line.

Aaron

What day did you catch it and what day did it arrive at ARS?

Oh look, who knows with days, I only think I caught it on a Wednesday, I know I worked in the city on a Friday, now whether I arrived on the Thursday or not I am not sure. Come to think of it, I am not even certain the Wednesday and Friday were in the same week.

Why can't they make it so that each line or group of lines runs separately from all others? Here in Melbourne they do and as a result, a fault on one line will only affect the group which that line is in, minimizing the disruption. In fact, in most cases it only affects that line.

Don't be ridiculous, that would be way too sensible to do here.

Why can't they make it so that each line or group of lines runs separately from all others? Here in Melbourne they do and as a result, a fault on one line will only affect the group which that line is in, minimizing the disruption. In fact, in most cases it only affects that line.

Not so smart? What happens in Melbourne or Sydney when the respective underground city loops go down?

In days of yore there were not centralised computers handling signalling function but distributed boxes of relays. There were also large numbers of appropriately trained employees to operate alternative safeworking procedures; those persons are now in short supply. Couple all this to todays regulatory environment and you have systems which grind to a halt at the slightest abnormality.

In Adelaide with it bus culture the short term solution is obvious.

Why can't they make it so that each line or group of lines runs separately from all others? Here in Melbourne they do and as a result, a fault on one line will only affect the group which that line is in, minimizing the disruption. In fact, in most cases it only affects that line.

Melbourne freeways must run like Adelaide's trains.   Accident on one = gridlock on all freeways for the next 3+ hours!

steam4ian, if there's a fault or emergency that affects all tunnels then the four groups of lines that use them will be affected, however, if only one of the tunnels is affected then only the group that uses that tunnel will be affected.

In Adelaide with it bus culture the short term solution is obvious.

Drive your car and avoid all of the unwashed masses.

In Adelaide with it bus culture the short term solution is obvious.

Drive your car and avoid all of the unwashed masses.

Aaron don't you mean "Drive your car and remain insulated (in your glass bubble) from the unwashed masses."?

There ain't no avoiding them on our roads unfortunately.