Why do we use wig-wags instead of normal traffic lights at level crossings?

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Peter350
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Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Peter350 » Wed Jul 21, 2021 10:05

This is probably a really stupid question since wig-wag signals have been established for decades, but why was it that these unique types of traffic signal were used in the first place rather than ordinary traffic lights for level crossings, lifting bridges, airports, fire stations etc?

I ask because there is at least one instance of a new junction that has been built right next to the crossing meaning ordinary traffic signals have now had to be placed in front of the wig-wags. The level crossing in Lymington was one of the first I ever encountered as a child, and as a result it was no surprise that I was saddened to discover it had fallen victim to this modification. The left traffic light completely blocks the view of the wig-wag on the same side, and once over the crossing you encounter another signal. This sort of mess makes me wonder whether we should just abolish wig-wags altogether and use ordinary traffic signals in their place, maybe with a flashing red phase to signify the same purpose as the double reds for a wig-wag.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Mark Hewitt » Wed Jul 21, 2021 10:35

It probably wasn't the original reason but I think ordinary red lights have a bunch of exceptions that allow you to pass on red, eg if you reasonably think the lights aren't working, if directed by a police officer etc. Whereas wigwags are absolute if they are flashing you don't cross beyond, no exceptions.

I suspect the real reason being more like they just developed in parallel. Two solutions for similar issues.
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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Peter350 » Wed Jul 21, 2021 16:33

Good point actually. I suppose the differentiation makes most sense for emergency vehicles since they can jump red lights while on call, but to do the same at a level crossing or lifting bridge would be impossible or extremely dangerous due to the road being blocked.

Even so, I suppose you could design a traffic light with four phases, the additional one being another red above the existing one which only flashes in scenarios where it would be dangerous for emergency vehicles to pass. Like this:

[O] Red
[O] Red
[O] Amber
[O] Green

Double red: All vehicles must stop - no exceptions (wig-wag locations only)
Single red: Stop (except in exceptional circumstances)

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by KeithW » Wed Jul 21, 2021 17:45

Wig-wag's make it clear this is not a normal road crossing which is important as fast trains are long, heavy and can be travelling at up to 125 mph. The stopping distance for a high speed train at 125 mph was given by the secretary of state for transport as :

2,568 metres using defensive driving brake application;
1,713 Metres using full service brake application; and
1,283 Metres using with an emergency brake application.

Worse still as on a level crossing trains are typically head on to you which makes judging crossing time very difficult.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Peter350 » Wed Jul 21, 2021 18:36

KeithW wrote:
Wed Jul 21, 2021 17:45
Wig-wag's make it clear this is not a normal road crossing which is important as fast trains are long, heavy and can be travelling at up to 125 mph. The stopping distance for a high speed train at 125 mph was given by the secretary of state for transport as :

2,568 metres using defensive driving brake application;
1,713 Metres using full service brake application; and
1,283 Metres using with an emergency brake application.

Worse still as on a level crossing trains are typically head on to you which makes judging crossing time very difficult.
But most level crossings are not on 125mph lines and the ones that remain are being replaced by bridges anyway. Besides, the function of my proposed signal would be the same, just a different design.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Conekicker » Wed Jul 21, 2021 19:10

Peter350 wrote:
Wed Jul 21, 2021 16:33
Good point actually. I suppose the differentiation makes most sense for emergency vehicles since they can jump red lights while on call, but to do the same at a level crossing or lifting bridge would be impossible or extremely dangerous due to the road being blocked.

Even so, I suppose you could design a traffic light with four phases, the additional one being another red above the existing one which only flashes in scenarios where it would be dangerous for emergency vehicles to pass. Like this:

[O] Red
[O] Red
[O] Amber
[O] Green

Double red: All vehicles must stop - no exceptions (wig-wag locations only)
Single red: Stop (except in exceptional circumstances)
What happens when one of the red aspects inevitably fails, you've lost your double red.
With a wig-wag that wouldn't be a problem.
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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Peter350 » Wed Jul 21, 2021 19:23

Conekicker wrote:
Wed Jul 21, 2021 19:10
Peter350 wrote:
Wed Jul 21, 2021 16:33
Good point actually. I suppose the differentiation makes most sense for emergency vehicles since they can jump red lights while on call, but to do the same at a level crossing or lifting bridge would be impossible or extremely dangerous due to the road being blocked.

Even so, I suppose you could design a traffic light with four phases, the additional one being another red above the existing one which only flashes in scenarios where it would be dangerous for emergency vehicles to pass. Like this:

[O] Red
[O] Red
[O] Amber
[O] Green

Double red: All vehicles must stop - no exceptions (wig-wag locations only)
Single red: Stop (except in exceptional circumstances)
What happens when one of the red aspects inevitably fails, you've lost your double red.
With a wig-wag that wouldn't be a problem.
Same as what would happen when one of the red phases fails on a wig-wag. As an aside, what is the existing protocol for when both red phases fail on a wig-wag?

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Gareth » Wed Jul 21, 2021 19:37

Emergency vehicles can go through red lights. Wig-wags allow no exemptions, for obvious reasons.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by avtur » Wed Jul 21, 2021 21:57

Peter350 wrote:
Wed Jul 21, 2021 19:23
Conekicker wrote:
Wed Jul 21, 2021 19:10
Peter350 wrote:
Wed Jul 21, 2021 16:33
Good point actually. I suppose the differentiation makes most sense for emergency vehicles since they can jump red lights while on call, but to do the same at a level crossing or lifting bridge would be impossible or extremely dangerous due to the road being blocked.

Even so, I suppose you could design a traffic light with four phases, the additional one being another red above the existing one which only flashes in scenarios where it would be dangerous for emergency vehicles to pass. Like this:

[O] Red
[O] Red
[O] Amber
[O] Green

Double red: All vehicles must stop - no exceptions (wig-wag locations only)
Single red: Stop (except in exceptional circumstances)
What happens when one of the red aspects inevitably fails, you've lost your double red.
With a wig-wag that wouldn't be a problem.
Same as what would happen when one of the red phases fails on a wig-wag. As an aside, what is the existing protocol for when both red phases fail on a wig-wag?
The level crossing I use everyday at Cooksbridge has two sets of wig wags and two single red flashing pedestrian lights operating in both directions, I think it is fair to say that they have covered redundancy.

Flashing lights are far more conspicuous than steady lights, which I would presume is why wig-wag lights are used on level crossings.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Dougman » Thu Jul 22, 2021 08:40

Peter350 wrote:
Wed Jul 21, 2021 19:23
Same as what would happen when one of the red phases fails on a wig-wag. As an aside, what is the existing protocol for when both red phases fail on a wig-wag?
The level crossing controls check that at least one red light is lit on each wig-wag, otherwise the crossing fails and it's notified to the signaller (or train driver at certain crossings). Trains then cross under caution.

I believe this is why both reds illuminate together at the start the flashing red sequence, so they can be proved lit.
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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Bryn666 » Thu Jul 22, 2021 10:49

Flashing reds were introduced with Automatic Half Barrier Crossings, previously full gate crossings were all manually controlled and a red disc on the gate acted as the stop sign. You can still see a few of these if you know where to look - there's one in Blackburn.

They were deliberately designed to be different to normal traffic lights because the consequences of being hit by a train are catastrophic, as we found at Hixon in 1968 when a low loader grounded on the crossing and was hit by a train.

After the Hixon disaster the steady amber was introduced. We are fairly unique in Europe as having a steady amber on level crossing lights I think?

The red and white backing board edge was a 90s invention, previously these were just white as many fire and ambulance station installations still have.
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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by WHBM » Thu Jul 22, 2021 11:46

The key thing about wigwags is they apply to much more than vehicles - starting with pedestrians.

The same is true of wigwags at eg fire station exits, that pedestrians should observe them to allow the fire engine to exit. I've never found anyone else who even thought about this as a requirement, though one or two said "good idea".

The difference with traffic signals is they are rarely used. Experience shows that conventional traffic signals which road users pass consistently which are always green get ignored on the odd occasion when they are red. This can be seen apparently (never seen them change myself) at signals at the entrance to tunnels, which get driven through if ever on red. This applies to wigwags too - certainly at our local fire station when I have stopped for them operating I have been overtaken, which appeared not to be knowing impatience but unknowing incompetence. This is why it's necessary to have lifting barriers as well at railway crossings, lifting bridges, etc.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Gareth » Thu Jul 22, 2021 18:55

Bryn666 wrote:
Thu Jul 22, 2021 10:49
After the Hixon disaster the steady amber was introduced. We are fairly unique in Europe as having a steady amber on level crossing lights I think?
Fairly unique in the world, even. Just the red wig-wags is the most common arrangement, though some European countries have a white light for when the crossing isn't activated which demonstrates that the crossing is functioning correctly.

France uses a single flashing red aspect.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by L.J.D » Thu Jul 22, 2021 19:30

Closed now permanently but this one in Barnsley has always used normal signals for it for some unknown reason right back to when the bus station used to pull out there and it had Mellors. Shame its gone now because it was quite unique. If you scroll forward you can actually see it in situ.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by WHBM » Thu Jul 22, 2021 20:49

Bryn666 wrote:
Thu Jul 22, 2021 10:49
After the Hixon disaster the steady amber was introduced.
This is one of those changes the British excel at, introducing features after an accident which have nothing to do with the accident. The vehicle in the Hixon accident, under police escort, had entered the crossing long before any warning light would have shown. It had not grounded, but was close, and was moving at snails' pace while accompanying staff were checking underneath in case this were to happen, when the crossing sequence started. The police did nothing - unlike some years later when at an automatic crossing on a major cycling race (I think it was the old "Milk Race") a policeman sent to control it actually gave a police raised stop handsignal to an approaching train after the crossing activated ! The train actually managed to stop. In fairness to the officer, having previously attempted to stop the cyclists and been universally ignored, it wasa last-ditch thing to try to stop the train.There was a similar event in recent times in France.

I believe there were some old-school crossings with traditional gates in town centres etc, from the days before wig-wags, which had normal traffic signals, just so the signalman could stop the heavy traffic to swing the gates.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Chris56000 » Thu Jul 22, 2021 22:30

Hi!

I think Germany used to have a colour–light system on their railways that differentiates between "Absolute Stop" or "Stop and Stay", called "Hp00" in their rule–book, shown with two red lights on a signal, and a "permissive stop" "Hp0", which is a single red, but they recognised the "danger–side failure" risk of this and replaced single–red "Hp0" with a red plus one white light "Zs0" permissive stop aspect that does fail safe in conjunction with a rule that no light in a signal (where one is usually shown) means "Absolute Stop" Hp00 if the red lamp in Aspect Zs0 goes out!

There is a wig–wag signalled fire station entrance about a mile from where I live down the B4152 half–a–mile past Streets Corner towards Aldridge, and this was switched on for the fire–engine to emerge whilst we were approaching it about a year and three months ago!

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by traffic-light-man » Thu Jul 22, 2021 22:41

Wig wags are intentionally different because they're for use in locations that, by their nature, means they are infrequently activated and activate at unpredictable times. Tunnels were permitted to use wig wags for a spell, but are now no longer authorised.

Like WHBM has mentioned, SGE particularly pushed their Autoflex Road Signals at their railway customers for the control of level crossings, which would've included regular RAG signals.

Germany also uses a leaving amber before red, though their red is a steady red.
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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by linuxrocks » Fri Jul 23, 2021 11:58

Did the UK ever use "proper" wigwags? We had them in Australia until the early 1960s I think.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by AndyB » Fri Jul 23, 2021 13:19

Ireland follows UK practice, except for automatic open crossings (known as lights and bells) which have no exit amber, although only the one on Wexford Quays still exists and has minimal risk due to a 5mph speed restriction on the entire quay section.

Curiously, at least one LC has advance amber wigwags for the benefit of drivers.

We went to Sweden in 2011. Red wigwags on AHBs, flashing lunar white below the wigwags on open crossings.

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Re: Why do we use wig-wags instead of normal traffic lights at level crossings?

Post by Chris Bertram » Fri Jul 23, 2021 15:14

traffic-light-man wrote:
Thu Jul 22, 2021 22:41
Germany also uses a leaving amber before red, though their red is a steady red.
This is a two-lamp signal, functioning like an RAG signal but with no green lamp. You find them at pedestrian crossings as well. The sequence is (blank) - A - R - R+A - (blank).
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