Driving question - do you ever have to slow down on clear aspects due to signal spacing?

[Egg Centric]

It seems to me (in my extensive experience on train simulators*) that there are occasionally sets of signals where YY-Y-R would be too short to actually pull up.

However it also seems to me (with my equally extensive experience on signalling simulators*) that in real life it seems that the signalling is actually wired to e.g. go YY-Y-Y-R or YY-YY-Y-R or similar when the signals are that close together.

So do you ever as a driver have to go slower than line speed (in good conditions) simply because of signal spacing? Or are you taught that you will always be able to pull up and route knowledge fills you in on the "extended" aspect sequences?

*I am available as a rail consultant at reasonable rates

 

[Magdalia]

So do you ever as a driver have to go slower than line speed (in good conditions) simply because of signal spacing?

Line speeds are set so that trains can stop safely. A good example is the up fast line on the ECML approaching Finsbury Park, where signals are close together and there is a differential speed limit set according to braking capability.

in real life it seems that the signalling is actually wired to e.g. go YY-Y-Y-R or YY-YY-Y-R or similar when the signals are that close together.

This goes back a long way, to the Great Eastern electrifications. I don't know if this still happens now, but the old signalling from the electrification era operated on triple double yellows that is G-YY-YY-YY-Y-R. At peak times it was rare for any signal to show a green light.

 

[whoosh]

The Midland Main Line approaching South Wigston on the down was Y - Y - R protecting the north side of the junction. The last two signals were way too close together for the linespeed. The first two signals were widely spaced though, and the final two on a curve, so it was really annoying crawling along. A good 80% of the time the junction would be clear by the time you got there.
I expect it's still the same there now.

I think Mountsorrel was the same, with a short section there too, so you would've had Y - Y - R.

Both of those with three aspect signals.

 

[66701GBRF]

As well as the above, you can also get a delayed release (approach release) on the previous signal if the section is short and the system doesn't use the extra yellows as described by others. There should never be a point where you are running on totally clear aspects and don't have enough space/time to stop at a red.

The thing with "simulators" (hobby sims) is they never implement signaling correctly. Either because the developers don't fully understand it or it's not regarded as important enough.

 

[driverd]

It seems to me (in my extensive experience on train simulators*) that there are occasionally sets of signals where YY-Y-R would be too short to actually pull up.

This tends to be a problem with train sims, rather than an accurate reflection of real life. It could be poor modelling of braking physics/gradient or poor recreation of the signalling system. In reality, certainly on the routes I drive (not in London so I can't speak for those areas), the far more common thing to get is YY-Y-R*-R (*where the first red is approach released to allow for the fact that there is insufficient braking distance between the first and second red). This set up tends to be in locations where colour lights have directly replaced semaphores, and in essence you're being checked to the home signal, which then clears to let you proceed to the section.

However it also seems to me (with my equally extensive experience on signalling simulators*) that in real life it seems that the signalling is actually wired to e.g. go YY-Y-Y-R or YY-YY-Y-R or similar when the signals are that close together.

This is one I've never knowingly encountered, though as a driver, such knowledge would never be shared with you as its a massive Spad trap on the day that the YY-Y-Y-R sequence is, infact, YY-Y-R. Obviously anticipation of anything other than the standard aspect sequence is a massive risk.

So do you ever as a driver have to go slower than line speed (in good conditions) simply because of signal spacing? Or are you taught that you will always be able to pull up and route knowledge fills you in on the "extended" aspect sequences?

I can't think of any particular examples where I would slow down for signal spacing alone in good conditions - there are examples in anticipation of a signal sequence where there is a risk of a wrong route but that's about all I can think of!

 

[Snow1964]

Simulators do whatever is programmed, and theirvrules might not reflect actual conditions.

Signals have been spaced on a W curve, it is decades old. Literally a graph of speed vs distance. It showed minimum spacing for the speed. It was based on tread braked coaches and was from memory under 7% g (gravity acceleration rate). Modern air braked stock with disc brakes is normally 9-10% g (nearer 12-15% g in emergency in good conditions). So modern trains can stop from 125mph on what was a 100mph signalled line.

 

[edwin_m]

The modern standard includes separate tables for use when all trains have 0%g braking. I can't say how often they are used, because it's probably pretty restrictive to ban the older train types. If the spacing has to be too short for some reason and it can't be addressed by a non-standard aspect sequence, then a speed restriction would have to be imposed, either for all trains or for those with poorer braking.

I recall reading that the track geometry at Reading would allow much higher speed than permitted, and the current limit is due to the signal spacing needed to achieve the capacity. If and when ETCS is fitted, this restriction could be eliminated because it monitors the speed against the actual braking capability of that train, and it isn't constrained by the limitation of only four signal aspects.

 

[Annetts key]

It seems to me (in my extensive experience on train simulators*) that there are occasionally sets of signals where YY-Y-R would be too short to actually pull up.

However it also seems to me (with my equally extensive experience on signalling simulators*) that in real life it seems that the signalling is actually wired to e.g. go YY-Y-Y-R or YY-YY-Y-R or similar when the signals are that close together.

So do you ever as a driver have to go slower than line speed (in good conditions) simply because of signal spacing? Or are you taught that you will always be able to pull up and route knowledge fills you in on the "extended" aspect sequences?

*I am available as a rail consultant at reasonable rates

Okay, a number of points to go through here.

When designing the signalling system, the line speed and braking capacity of the trains that will use it are taken into account. As are any changes in gradient. However, the location of junctions, points, diamond crossings, structures (including bridges, tunnels, stations) or other features may limit where signals can be positioned.

The normal standard is to have service braking distance (plus an allowance) between the first caution aspect and the signal at red / danger, taking into account all the factors I listed above. The signals are then spaced to take all this into account. There are signalling plans that show the exact distance between each signal and the line speed for every available combination for the layout.

For a four aspect area, that means between the signal showing double yellow (YY) and the signal showing red.

So:

S1 --- S3 --- S5 --- S7
G      YY     Y      R
       |<----------->| is service braking distance.

The use of YY-Y-Y-R or YY-YY-Y-R is not normally permitted, because it can lead drivers into a trap.

S1 --- S3 --- S5 --- S7 --- S9
G      YY     Y      Y      R

In the above case, if signal S7 was actually at red, as shown below:

S1 --- S3 --- S5 --- S7 --- S9
G      YY     Y      R      R

A driver may have become accustomed to not slowing sufficiently at S3 or S5 to actually stop at signal S7.

Similarly with:

S1 --- S3 --- S5 --- S7 --- S9
G      YY     YY     Y      R

Again, if S7 is red, a driver may have become accustomed to not slowing sufficiently at S3 or S5 to actually stop at signal S7.

If for any reason service braking distance cannot be achieved, say for example that a junction has been relaid or remodelled with higher speed points or a different layout, and hence the protecting signal has had to be moved towards the direction trains approach from. Then either a permanent speed restriction will need to be applied, or one of the signals will have to be provided with special controls.

For example, the distance between S7 and S9 is insufficient, with no route set from S9:

S1 --- S3 --- S5 --- S7 --- S9
G      YY     Y      R      R

As a train approaches S7, this signal will clear to a single yellow:

S1 --- S3 --- S5 --- S7 --- S9
YY     Y      R train Y      R

However, if S9 is showing a proceed aspect you get this (assuming there is service braking distance between S7 and S11):

S1 --- S3 --- S5 --- S7 --- S9 --- S11
G      G      G      YY     Y      R

I hope that explains the normal practice. Of course, there may be places where non-standard aspect sequences exist.

Note that if there is a signal equipment failure, it's possible to have unusual aspect sequences, but the train will always have service braking distance, it's just that the driver will not know this from the aspect(s) they are seeing. This is the case for protected "right side" failures.

 

[whoosh]

If for any reason service braking distance cannot be achieved, say for example that a junction has been relaid or remodelled with higher speed points or a different layout, and hence the protecting signal has had to be moved towards the direction trains approach from. Then either a permanent speed restriction will need to be applied, or one of the signals will have to be provided with special controls.

I'm sure the presence of a speed restriction (maybe due to non-standard overlap - which may be a slightly different circumstance from what the OP was looking for in this thread, admittedly) was mentioned in the report about the Watford crash of 1996.

 

[baz962]

The Midland Main Line approaching South Wigston on the down was Y - Y - R protecting the north side of the junction. The last two signals were way too close together for the linespeed. The first two signals were widely spaced though, and the final two on a curve, so it was really annoying crawling along. A good 80% of the time the junction would be clear by the time you got there.
I expect it's still the same there now.

I think Mountsorrel was the same, with a short section there too, so you would've had Y - Y - R.

Both of those with three aspect signals.

It most definitely is still the same. Double blocking the junction and crawling by the time you see what is/was the red at Wigston .

 

[InkyScrolls]

It seems to me (in my extensive experience on train simulators*) that there are occasionally sets of signals where YY-Y-R would be too short to actually pull up.

However it also seems to me (with my equally extensive experience on signalling simulators*) that in real life it seems that the signalling is actually wired to e.g. go YY-Y-Y-R or YY-YY-Y-R or similar when the signals are that close together.

So do you ever as a driver have to go slower than line speed (in good conditions) simply because of signal spacing? Or are you taught that you will always be able to pull up and route knowledge fills you in on the "extended" aspect sequences?

*I am available as a rail consultant at reasonable rates

Simulators are not real life! There will never be an occasion where it isn't possible to stop within the visible signal sequence.

 

[Annetts key]

I'm sure the presence of a speed restriction (maybe due to non-standard overlap - which may be a slightly different circumstance from what the OP was looking for in this thread, admittedly) was mentioned in the report about the Watford crash of 1996.

Overlaps are separate to the aspect sequence and to the length of the service braking area. They are provided ahead of (beyond) signals (that can show a red aspect) on passenger lines, mixed traffic lines (and in certain cases on goods lines) to provide a safe area of 200 yards (183m) should a train overrun past a signal at red. In the situation with the signal at Watford, the overlap was shorter than normal, so a permanent speed restriction was put in place in order to comply with the standards at the time. Unfortunately the position of the permanent speed restriction was incorrect.

If there is insufficient distance between signals to achieve service braking distance, a permanent speed restriction is likely to be a non-preferred solution. It's a non-preferred solution, as it will slow trains when they are running on clear (green) aspects.

One thing I should make clear is that what the driver of a train sees, is a snapshot in time for each signal. The driver may not be able to see more than one signal at the same time, so they may not see the full aspect sequence that all the relevant signals are showing instantaneously. This distinction is important, as a signal with special controls may step up to a less restrictive aspect after the train passes the previous signal, but before the driver is able to see the signal that has special controls. This is likely if the line is on a long curve or has multiple bends, or there are bridges that limit viewing distances. So a driver on a train would see a different aspect sequence compared to them walking along the track.

This is because a signal with the special controls may step up to a less restrictive aspect when the train is detected approaching this signal via track circuits or axle counters.

Hence with this example:

S1 --- S3 --- S5 --- S7 --- S9
G      YY     Y      R      R

Where signal S7 has special controls, the driver will see S3 at double yellow, S5 at single yellow, but may not see S7 showing red because it has stepped up to show a single yellow before it comes into view.

 

[King Lazy]

While the posters who have said that you should be able to stop within the normal sequence from Green to Red starting at line speed there appear to have historically been instances where issues have been raised with that. I say appear because I’m basing it on unconfirmed stories I’ve been told that imply issues have been raised with the braking distance after the signalling has been commissioned rather than being designed out initially.
Although the stories I’ve heard could equally be a properly planned change after initial commissioning.

One such example is approaching Carlisle on the down WCML. If the signal protecting the station is at danger then the sequence towards it is

G—YY—YY—Y—R

I am told this was because Class 50 locomotives had trouble with the braking distance from the double yellow towards the red. Therefore the signal in the rear of the double yellow was also restricted to double yellow when the signal protecting the station is at danger thus extending the braking distance from the first sighting of a cautionary aspect.

Now I don’t know how true this is. And I also don’t know if the change was made prior to the introduction of the Class 50 or was flagged afterwards after drivers reported an issue stopping.

Or maybe the change was made to allow a higher line speed and is nothing to do with Class 50s (many railway stories turn out to be one person’s assumption of why a change is made when the real reason is different).

I also don’t know what the line speed at that time was. I suspect 75.

It is currently 90 at both double yellows though the 2nd is after a warning for a 20 psr (which begins after the red) and I personally think that while it is possible to stop in that distance it is not not something I would feel comfortable with especially in less than good weather. And I’d probably be less comfortable in older traction like a class 50 with a heavy load.

Edit.

To attempt to show the layout a little clearer see my terrible diagram.

I’ve tried to show the rough spacing as well. It’s a long run between the first YY and second YY then the next sections are much shorter.

20W is the warning for the 20 PSR

YY - - - - 20W - - YY - - - Y - - - R 20

 

[driver9000]

While the posters who have said that you should be able to stop within the normal sequence from Green to Red starting at line speed there appear to have historically been instances where issues have been raised with that. I say appear because I’m basing it on unconfirmed stories I’ve been told that imply issues have been raised with the braking distance after the signalling has been commissioned rather than being designed out initially.
Although the stories I’ve heard could equally be a properly planned change after initial commissioning.

One such example is approaching Carlisle on the down WCML. If the signal protecting the station is at danger then the sequence towards it is

G—YY—YY—Y—R

I am told this was because Class 50 locomotives had trouble with the braking distance from the double yellow towards the red. Therefore the signal in the rear of the double yellow was also restricted to double yellow when the signal protecting the station is at danger thus extending the braking distance from the first sighting of a cautionary aspect.

Now I don’t know how true this is. And I also don’t know if the change was made prior to the introduction of the Class 50 or was flagged afterwards after drivers reported an issue stopping.

Or maybe the change was made to allow a higher line speed and is nothing to do with Class 50s (many railway stories turn out to be one person’s assumption of why a change is made when the real reason is different).

I also don’t know what the line speed at that time was. I suspect 75.

It is currently 90 at both double yellows though the 2nd is after a warning for a 20 psr (which begins after the red) and I personally think that while it is possible to stop in that distance it is not not something I would feel comfortable with especially in less than good weather. And I’d probably be less comfortable in older traction like a class 50 with a heavy load.

Edit.

To attempt to show the layout a little clearer see my terrible diagram.

I’ve tried to show the rough spacing as well. It’s a long run between the first YY and second YY then the next sections are much shorter.

20W is the warning for the 20 PSR

YY - - - - 20W - - YY - - - Y - - - R 20

I wonder if that's reserved for certain trains because when I approach Carlisle on the Down with the red protecting the station I am usually brought down on the normal green to red sequencing with the signal at Brisco showing green. More often than not these days we are signalled straight through the station on greens anyway.

There are certainly locations on my route card that need a good amount of brake to slow the train under normal sequencing but we know where they are and to react on sighting the signal if necessary.

 

[King Lazy]

Possibly.

I’ve never had more than one green after the M6 if the signal protecting the station is Red and was told it shouldn’t be possible?

By Brisco do you mean the signal directly after the motorway? Or the one on the left hand curve before the straight towards Upperby Bridge as they’re either side of the old station site but the latter is nearer the village?

If the signals are permanently restricted as I was led to believe rather than on a per train basis then the last green should be immediately after the M6 viaduct at Newbiggin Hall followed by YY (Brisco) YY (Upperby Bridge) Y (Upperby) R (St Nicholas).

Usually if there is YY immediately after the M6 I tend to believe it a train ahead based on my understanding of the signalling there.

But if I see a green after the M6 and the next signal on the left hand curve before the straight is also Green then I’ve never then had YY at Upperby Bridge Y at Upperby and a red protecting the station.

I was led to believe the YY at Upperby Bridge junction restricts the previous one to YY also but due to the curve it’s not possible to see them both.

I think only once have I seen YY on the curve at Brisco and then Y at Upperby Bridge.

Almost every time I see YY at the curve Upperby Bridge is also YY on sighting it though occasionally it has stepped up to Green.

 

[43066]

It seems to me (in my extensive experience on train simulators*) that there are occasionally sets of signals where YY-Y-R would be too short to actually pull up.

However it also seems to me (with my equally extensive experience on signalling simulators*) that in real life it seems that the signalling is actually wired to e.g. go YY-Y-Y-R or YY-YY-Y-R or similar when the signals are that close together.

So do you ever as a driver have to go slower than line speed (in good conditions) simply because of signal spacing? Or are you taught that you will always be able to pull up and route knowledge fills you in on the "extended" aspect sequences?

*I am available as a rail consultant at reasonable rates

In my very limited experience of train sims (really just BVE years ago), the signals didn’t “pop” anything like as much as they do in real life and appeared just to blend into the background. I wonder if that has something to do with it as you’re not able to react as quickly to an aspect as a driver would in real life?

 

[Egg Centric]

In my very limited experience of train sims (really just BVE years ago), the signals didn’t “pop” anything like as much as they do in real life and appeared just to blend into the background. I wonder if that has something to do with it as you’re not able to react as quickly to an aspect as a driver would in real life?

I've not actually encountered colour lights where it's been a problem to stop in the sim in practice (I have encountered absolute block where the distant's been off incorrectly but that's another matter) but I have noticed that some it would be hard for me to pull it up if I'd needed to.

Re the very specific issue you describe that is a problem in train sim world but there is a patch for it

 

[driver9000]

Possibly.

I’ve never had more than one green after the M6 if the signal protecting the station is Red and was told it shouldn’t be possible?

By Brisco do you mean the signal directly after the motorway? Or the one on the left hand curve before the straight towards Upperby Bridge as they’re either side of the old station site but the latter is nearer the village?

If the signals are permanently restricted as I was led to believe rather than on a per train basis then the last green should be immediately after the M6 viaduct at Newbiggin Hall followed by YY (Brisco) YY (Upperby Bridge) Y (Upperby) R (St Nicholas).

Usually if there is YY immediately after the M6 I tend to believe it a train ahead based on my understanding of the signalling there.

But if I see a green after the M6 and the next signal on the left hand curve before the straight is also Green then I’ve never then had YY at Upperby Bridge Y at Upperby and a red protecting the station.

I was led to believe the YY at Upperby Bridge junction restricts the previous one to YY also but due to the curve it’s not possible to see them both.

I think only once have I seen YY on the curve at Brisco and then Y at Upperby Bridge.

Almost every time I see YY at the curve Upperby Bridge is also YY on sighting it though occasionally it has stepped up to Green.

I'm referring to the signal on the left hand curve after the site of the former Brisco station (ie the one before the 20 warning board). I've had that signal showing green and the next one at Upperby Bridge showing YY countless times. Equally there's numerous times I've had YY at Brisco coming through the left hand curve and seen Upperby Bridge showing Y and then a Red at Upperby or Upperby Bridge steps up as I run along the straight.

 

[King Lazy]

In that case it must not be wired as I was told and probably I’m guilty of confirmation bias and only remember the situations where things have conformed to my understanding.

I suspect it may have changed over the years but I am sure (or at least I was!) that at one time the signals were wired such that both the signals at Upperby Bridge and Brisco had to display double yellow if no forward route was set into the station.

I’m surprised it’s changed given that it’s possible to run a pair of 50s on a charter but perhaps TPWS over speed protection has provided the mitigation necessary to remove the restriction on the signals.