Wig-wag light behaviour

[tom66]

I've noticed that when wig-wags activate, you get a yellow phase, then both red lamps on, then one switches off and the oscillation between the two red lights seems to speed up over a few cycles. This almost seems a little 'wrong', as if it is an oscillator slowly starting up, in an age of modern digital electronics.

e.g. here: https://www.youtube.com/watch?v=-7RXWRkztyw

The first few are LED only and it seems like they replicate this pattern in a very digital manner, the one at 4:20 onwards seems to have a more analog behaviour.

Now I had thought this may be because older analog or relay-based oscillators were used, but it seems like this applies to crossings which have had their heads replaced with LED units. I'm not sure if the controllers have been upgraded too, so this is speculation, but has the behaviour been replicated in these units to emulate the older lamp behaviour? If so, is there a safety case for it? Does it allow some kind of system test? Or is it just "because we've always done it that way"?

[Nathan_A_RF]

It can actually vary crossing to crossing but this starting sequence is the most common. Sometimes the amber is followed directly by alternate flashing, sometimes both reds show and immediately alternate flashing. I'm not sure about the detailed reasoning but not sure about a safety test, as I've seen videos of crossings with both halogen and LED units broken.

[traffic-light-man]

I believe that the vast majority of Network Rail crossings still use relays, and the Unipart Dorman LED units have been designed to work with those, which probably explains this behaviour. It does seem to be a trait only seen at level crossings, though, I don't think I've ever seen traffic signal derived ones do it, even the ones running on old GEC controllers which still used relays.

[AndyB]

I'm sure I've read somewhere that the two reds flash together once to prove they are working.