Great Western to be wired for 140!

[whole diary]

[bobm]

XC^▸ (Cross Country Trains (franchise)) do occasionally use the "fast lines" (or main as they are called in GWR^▸ (Great Western Railway) land) from Reading but they are limited to, I think, 100mph.  They then turn right just before Didcot Parkway and shortly thereafter the remaining GW^▸ (Great Western) services towards Swindon only have a choice of one line in each direction after Foxhall Junction - apart from some lengthy loops in the Challow area.

In 1967 Foxhall Junction was the scene of a derailment where a driver's route knowledge let him down and he made the transition from a four track railway to a two track one at excessive speed and came off the road.

[eightf48544]

Also, for 140mph running on GWML^▸ (Great Western Main Line), does it really have to wait until the lineside signals are removed? I thought stock that actualy has ETRMS fitted would run with cab signaling as if the lineside signals weren't there, but the lineside signals would be left so trains that don't have ETRMS can still be used.

That's exactly what happens on DB^» (Deutsche Bahn - German State Railway - about) on suitable lines. You can watch the driver reprogramme the computer for the LZB fitted sections. A yellow pointer appears on the Speedo to incate the maximum line speed the train can run at, but you still have lineside signals on normal lines.  This allows speeds up to 300kph but not on all lines.

[Tim]

I thought the problem with the flashing greens was that it was too hard to tell whether they were flashing or not when traveling at high speed. That's just what I've read somewhere.

That's right - and you have to see the full sequence of the flashing, which takes too long, or might not be pssoible on curves.   Otherwise a green that just failed at the very instant you approached it could be mistaken for a flash off.  I also suspect that a steady green can appear to flash just the same if sighting is affected by fleeting obstructions between the viewer and the signal - such as signal gantries.
Speed up the flashing, and persistence of vision might be a problem, especially with the time taken for a filament lamp to go off and on. (Possibly better with LEDs though)

Flashing aspects never seemed very safe to me.  Wouldn't it have been better to add an extra light so "double green" would mean the higher permitted speed.

[paul7575]

Flashing aspects never seemed very safe to me.  Wouldn't it have been better to add an extra light so "double green" would mean the higher permitted speed.

The problem with that is it is contrary to what happens with double yellow, where the double aspect is a more restrictive aspect than the single, and all the signals on the route would have needed a fifth lamp to provide the new aspect anyway. 

Part of the aim was apparently to avoid new hardware, so that wouldn't have met the requirement.

Likewise a completely new colour was suggested, but this also needed additional hardware, and (I'm fairly sure) the more colours you use, the more problems with colour eyesight standards you get...

Paul

[bobm]

The problem with that is it is contrary to what happens with double yellow, where the double aspect is a more restrictive aspect than the single, and all the signals on the route would have needed a fifth lamp to provide the new aspect anyway. 

Would they all need a fifth lamp?  With the move to LED signal heads could not the second head (currently used to display the second yellow) also display a second green when required?

[Zoe]

The problem with that is it is contrary to what happens with double yellow, where the double aspect is a more restrictive aspect than the single, and all the signals on the route would have needed a fifth lamp to provide the new aspect anyway. 

Double yellow is not more restrictive than single yellow.

[paul7575]

The problem with that is it is contrary to what happens with double yellow, where the double aspect is a more restrictive aspect than the single, and all the signals on the route would have needed a fifth lamp to provide the new aspect anyway. 

Double yellow is not more restrictive than single yellow.

That's right - no idea why I wrote that... 

Paul

[paul7575]

Would they all need a fifth lamp?  With the move to LED signal heads could not the second head (currently used to display the second yellow) also display a second green when required?

They would have needed a fifth lamp at the time of the trial, because LED versions were not yet available - they might not even have been possible - when did reliable colour LEDs start appearing on road trafffic lights for instance?

Portsmouth resignalling used filament lamps, which is only a few years ago, so that perhaps defines when the transition to LEDs on the railway was in progress?

Paul

[broadgage]

Years ago, when flashing green signals were first considered, a double green aspect was I believe considered.
It was indeed rejected at the time due to the extra hardware needed, whereas a flashing green simply required an extra circuit to make the existing lamp flash or light steadily.

However as others post, technology moves on and with LED lit signals a double green is easily achieved.
Only four signal lamps would be needed, since each can display several colours.

It would be a relatively simple matter to display
double green
single green
double yellow
single yellow
red

As required.
if the driver failed to to see one of the two green lights that would simply result in a needless reduction in speed from 140 to 125 MPH, say, and would not be a cause of danger.
The double green would be less restrictive than a single green just as a double yellow is less restrictive than a single yellow.

[Zoe]

Could it have been an option to have used green and yellow as a new aspect less restrictive than double yellow but more restrictive than green?  This would not have required another light to have been installed.  One issue I can see with this though would have been having two aspects next to each other illuminated at the same time, I'm not sure if that would have been allowed.

[broadgage]

Another advantage of LED lit signals is that the brightness of the light may be easily altered so as to be suitable for the conditions.
AFAIK^▸ (as far as I know) this is not used at present for railway signals*

On high speed lines it would seem desireable to make the signals brighter during bright daylight, in order that the driver may have the best possible view.
In sunlight, the brighter the better, within reason.

Brighter signals have been considered in the past, but have been rejected on the grounds of excessive power usage, and glare at night.

About the present intensity at night, and perhaps twice or more in daylight would improve daylight signal sighting and together with double green signals perhaps allow higher speeds with conventional signalling.

*many road traffic signals DO dim at night, to avoid glare at night but ensure good daytime visability.

[Electric train]

Years ago, when flashing green signals were first considered, a double green aspect was I believe considered.
It was indeed rejected at the time due to the extra hardware needed, whereas a flashing green simply required an extra circuit to make the existing lamp flash or light steadily.

However as others post, technology moves on and with LED lit signals a double green is easily achieved.
Only four signal lamps would be needed, since each can display several colours.

It would be a relatively simple matter to display
double green
single green
double yellow
single yellow
red

As required.
if the driver failed to to see one of the two green lights that would simply result in a needless reduction in speed from 140 to 125 MPH, say, and would not be a cause of danger.
The double green would be less restrictive than a single green just as a double yellow is less restrictive than a single yellow.

Or much simpler on the GWML^▸ (Great Western Main Line) as it is getting new I/C stock, refurb's stock for TV lines and Crossrail and the GWML signaling is up for renewal to install ETRMS Level 2 so the new trains can run on in the cab signaling and the older trains on line-side

[paul7575]

However as others post, technology moves on and with LED lit signals a double green is easily achieved.
Only four signal lamps would be needed, since each can display several colours.

Using the current technology it can be done with only two multi-colour LED heads.
The lower gives red, yellow, or green;  the upper gives yellow or green.

Not all LED installations are the same though, sometimes you do get a separate head for each colour, even with LEDs.

I can still think of other pitfalls not mentioned yet though.  For instance, differentiating visually between single and double yellow at caution speeds is probably not the same as differentiating one or two of the same colour green when running at 140 mph.  Another point which just occured, if your 140 mph section is pretty straight, what happens if at night you can see not just the next signal but a number of others behind it?

All a bit academic now of course...

Paul


  

[IndustryInsider]

XC^▸ (Cross Country Trains (franchise)) do occasionally use the "fast lines" (or main as they are called in GWR^▸ (Great Western Railway) land) from Reading but they are limited to, I think, 100mph. 

XC use the fast lines more than occasionally, getting on for half of the time in fact (I think 'Up' Bournemouth's are normally routed on the Main lines, as are the 'Down' Newcastle's), and they are not limited to 100mph and are able to do the full 125mph on that section.

Worth pointing out that in the ITT^▸ (Invitation to Tender) documents, the Relief lines are to be increased from 100mph to 125mph anyway during the GWML^▸ (Great Western Main Line) electrification programme:

The Department has asked Network Rail to deliver line speed improvements at the same time as electrification including 125mph on the slow lines between Reading and Didcot.

[Btline]

What about ATP^▸ (Automatic Train Protection) for the XC^▸ (Cross Country Trains (franchise)) running at 125?