[update: the system I call the ‘Irish’ system below, is not distinctive of Ireland at all, as is pointed out in the comments.]
Irish traffic lights differ from ones I have seen elsewhere. The light sequence is Green, Amber, Red, Green,… (unlike for instance, the UK where the lights go Green, Amber, Red, Amber, Green, Amber, … Incidentally, I like the UK’s amber phase before lights go green, because it gives you a moment to get ready to go. I don’t think the amber phase before red is much use at all, since most motorists just treat it as a reason to speed up.)
The distinctive feature of Irish traffic lights, I think, is the way they control the movement of separate streams of turning traffic and traffic continuing straight ahead. Irish traffic lights use a combination of a full red light and a green directional arrow to express the fact that traffic moving in the direction of the arrow (whether turning or going straight ahead) may move, but traffic going in other directions may not.
I need pictures for this, but couldn’t find any online so these schema will have to do:
means traffic turning right may go but traffic going straight ahead or left must stop.
This practice contrasts with New Zealand and the UK, for instance, which use a general go signal in combination with a red directional arrow prohibiting particular paths.
(i.e. traffic turning left remain stationary, other traffic may go).
On the Irish system, when the traffic going straight-ahead may go but all turning traffic must stay stopped, you have a green arrow pointing straight ahead and a full red stop light.
The system obviously works just fine in practice, but I don’t like it and here’s why the other system is better.
The Irish system gives inconsistent instructions to the driver whereas the other system gives discriminating advice. A full red stop light is a general injunction to stop. So when you see a red light and a green arrow, it is telling the traffic travelling in the direction of the arrow both to go (because of the arrow) and to stop because of the full red light. Since the red light is general it applies to the traffic going in the direction of the arrow as much as to other traffic. So the message is inconsistent. Go and don’t go.
The other system on the other hand is discriminating. A arrow of any colour is not general. It applies only to traffic going in the direction of the arrow, so a red directional arrow merely qualifies a full green go light. It says ‘Go (but not this way)’. The red arrow strikes off otherwise admissible paths. The message overall is consistent.
P.S. To those of you who say, ‘big deal, who cares?’ or ‘cough-autistic-cough’ I say, ‘harrumph. You probably also don’t care which way the toilet paper rolls off the roll. Off over the roll is obviously much better!’
Here’s a nice cartoon over at xkcd that speaks to the subject of this post.