Track circuits at level crossings?

[High Dyke]

Incidentally, do you know how the interlocking deals with this, in normal signalling? Ordinarily, a route set over the crossing would prevent the barriers raising after one's passed on the other road. Does auto-lower somehow inhibit this, instead putting it's own separate request into the interlocking?

A more technically minded person may be able to explain it better, but from experience then it works just the same.

 

[MarkyT]

Incidentally, do you know how the interlocking deals with this, in normal signalling? Ordinarily, a route set over the crossing would prevent the barriers raising after one's passed on the other road. Does auto-lower somehow inhibit this, instead putting it's own separate request into the interlocking?

Crossing controls can be in the signal/aspect level of the interlocking only, rather than also being in the route setting and locking levels. That's how traditional 'slotting' with a local attendant's cabin is achieved. A PSB can set routes at will but the signal will not clear until the slot from the local cabin is received, confirming crossing clear. Similarly, the crossing locking holding the gates down can be arranged to disengage once the train has passed clear, even if the route remains set. Once a signal has cleared over the crossing it becomes locked and the interlocking will deal with multiple trains safely. If a route is cancelled with a train approaching, an approach locking timer holds the locking for a time to avoid risk from overruns. An attendant is usually alerted to the need to close the crossing by an annunciator, which is designed to give good warning of an approaching train from track circuits being occupied to allow the keeper to operate the crossing in time to avoid any adverse signal aspects. In multi-aspect areas, The 1st initiating TCs can be several signal sections away from the crossing for sufficient time and the system wouldn't look back beyond signals that at red and free of approach locking. Such an anunciator circuit contains logic very similar to that needed to trigger auto-lower. There's also a control for minimum road open time at double-track AHBCs. The strike in point is positioned 10 seconds further out than actually required and a 10 second timer runs before the road warnings start. This allows the crossing controls to determine there is no other train about to approach in the opposite direction which, with normal warning times, could result in a road open time of less than 10 seconds, considered unsafe. If there is another such train approaching closely, the barriers will remain lowered with red lights flashing for the next train.

 

[Taunton]

What happened to "Second Train Coming" warning lights for road users. They used to be installed (sparingly, it seemed), they were in The Highway Code, but were then dispensed with.

 

[MarkyT]

What happened to "Second Train Coming" warning lights for road users. They used to be installed (sparingly, it seemed), they were in The Highway Code, but were then dispensed with.

On the fixed notices at crossings it now says if red lights continue to flash another train is coming. I don't know the reasoning for abandoning the separate illuminated sign but it's absence means less to maintain and renew.

 

[John Webb]

What happened to "Second Train Coming" warning lights for road users. They used to be installed (sparingly, it seemed), they were in The Highway Code, but were then dispensed with.

On the fixed notices at crossings it now says if red lights continue to flash another train is coming. I don't know the reasoning for abandoning the separate illuminated sign but it's absence means less to maintain and renew.

According to Stanley Hall and Peter Van Der Mark's book "Level Crossings" (Ian Allan, 2008, ISBN 0 7110 3308 0) Chapter 7 recounts how in 1977 a Working Party from the Railway Inspectorate, BR and Dept of Transport was convened. They paid several visits to Europe to view practices on the continent. One recommendation that arose from this Working Party was the replacement of the expensive neon-powered "Second Train Coming" sign by the fixed sign. It seems this and other recommendations were incorporated into a new booklet of requirements published in 1981.

 

[MarkyT]

According to Stanley Hall and Peter Van Der Mark's book "Level Crossings" (Ian Allan, 2008, ISBN 0 7110 3308 0) Chapter 7 recounts how in 1977 a Working Party from the Railway Inspectorate, BR and Dept of Transport was convened. They paid several visits to Europe to view practices on the continent. One recommendation that arose from this Working Party was the replacement of the expensive neon-powered "Second Train Coming" sign by the fixed sign. It seems this and other recommendations were incorporated into a new booklet of requirements published in 1981.

Being neon, the original equipment would have needed a high voltage AC supply, difficult to provide back-up for at a crossing site where everything else usually runs at 24VDC. Solid state step-up voltage converters and inverters were expensive and less reliable technology in the 1960s and 70s. Also, the tubes were likely delicate, needing careful handling, possibly being vulnerable to minor shocks in service. In short a maintenance headache. Today, numerous manufacturers could make a very robust low power/voltage LED version and I note some are available in the USA where the FRA has investigated their effect on pedestrian behaviour particularly.

https://railroads.dot.gov/elibrary/effect-active-another-train-coming-warning-system-pedestrian-behavior-highway-rail-grade

The Federal Railroad Administration (FRA) was interested in evaluating a type of grade crossing safety enhancement which alerts pedestrians at the crossing to the presence of a second train. The system chosen for this analysis, known as an Another Train Coming Warning System (ATCWS), consists of signage and an accompanying aural alert which is activated by the presence of multiple trains during gate activation. The ATCWS was installed at a crossing in Garfield, NJ, to assess the impacts of such a warning system on pedestrian behaviors during gate activations with multiple trains. Pedestrian violations were therefore tracked before and after the installation of the ATCWS. No difference was found in the number of violators during a second train activation before and after the installation of the ATCWS. However, small sample sizes and extreme weather during the data collection period indicate that further testing is necessary before strong conclusions about the effects of an ATCWS can be reached.

 

[John Webb]

Being neon, the original equipment would have needed a high voltage AC supply, difficult to provide back-up for at a crossing site where everything else usually runs at 24VDC. Solid state step-up voltage converters and inverters were expensive and less reliable technology in the 1960s and 70s. Also, the tubes were likely delicate, needing careful handling, possibly being vulnerable to minor shocks in service. In short a maintenance headache. Today, numerous manufacturers could make a very robust low power/voltage LED version and I note some are available in the USA where the FRA has investigated their effect on pedestrian behaviour particularly.

https://railroads.dot.gov/elibrary/effect-active-another-train-coming-warning-system-pedestrian-behavior-highway-rail-grade

I do wonder when they say 'Neon' if they were actually speaking of 'fluorescent' tubes. Just that I can't see a proper 'neon' tube having the brightness needed for daylight viewing. I also recall older relatives in the late 1950s referring to fluorescent tubes as 'Neons'.
I agree that modern LEDs should be able to make a much better 'Second Train coming' sign if thought desirable.

 

[MarkyT]

I do wonder when they say 'Neon' if they were actually speaking of 'fluorescent' tubes. Just that I can't see a proper 'neon' tube having the brightness needed for daylight viewing. I also recall older relatives in the late 1950s referring to fluorescent tubes as 'Neons'.
I agree that modern LEDs should be able to make a much better 'Second Train coming' sign if thought desirable.

I don't recall ever seeing one first-hand. Here's a YT movie showing an illuminated ATC sign in action.

I don't think you could flash ordinary flourescent lighting tubes like that reliably.
Other descriptions detail letters individually formed by the neon tubes, behind a glass screen with a protective mesh. BR/RT/NR took a while to remove them all apparently, with final examples surviving into the early 2000s.

 

[John Webb]

I don't recall ever seeing one first-hand. Here's a YT movie showing an illuminated ATC sign in action.

I don't think you could flash ordinary flourescent lighting tubes like that reliably.
Other descriptions detail letters individually formed by the neon tubes, behind a glass screen with a protective mesh. BR/RT/NR took a while to remove them all apparently, with final examples surviving into the early 2000s.

Thanks - I hadn't appreciated they flashed, which does make a difference.