OT - Traffic Lights

[DerbyBorn]

I was just reading about traffic light controllers:

"Attempts are often made to place traffic signals on a coordinated system so that drivers encounter a green wave, a long string of green lights (the technical term is progression). The distinction between coordinated signals and synchronized signals is very important. Synchronized signals all change at the same time and are only used in special instances or in older systems. Coordinated (progressed) systems are controlled from a master controller and are set up so lights "cascade" (progress) in sequence so platoons of vehicles can proceed through a continuous series of green lights. A graphical representation of phase state on a two-axis plane of distance versus time clearly shows a "green band" that has been established based on signalized intersection spacing and expected vehicle speeds.[14] In some countries (e.g. Germany, France and the Netherlands), this "green band" system is used to limit speeds in certain areas. Lights are timed in such a way that motorists can drive through without stopping if their speed is lower than a given limit, mostly 50 km/h (30 mph) in urban areas. This system is known as "gr?ne Welle" in German, "vague verte" in French, or "groene golf" in Dutch (English: "green wave"). Such systems were commonly used in urban areas of the United States from the 1940s, but are less common today. In the UK, Slough in Berkshire had part of the A4 experimented on with this. Many US cities set the green wave on two-way streets to operate in the direction more heavily traveled, rather than trying to progress traffic in both directions. But the recent introduction of the flashing yellow arrow (see Traffic-light signalling and operation) makes the lead-lag signal, an aid to progression, available with protected/permissive turns."

This all sounds good - why are we in the dark ages. I have also seen examples of the count-down timer on lights which makes for a faster getaway (or a realxing wait), but I guess it would be seen as dangerous in our nanny state.

[Nightjar]

Until 2009, it was official DfT policy to discourage the use of green waves, as they save fuel and hence reduce the revenue from fuel duties.

I doubt that local authorities immediately ran out and changed all their controllers. You may see green waves appearing as systems are replaced or updated though.

I suspect they would be difficult to implement where the interval between changes is dynamic, rather than a fixed period.

[Scott M]

[snip]

What makes you think ours don't work like this? Newly installed sets are jammed full of software, timers, cameras & sensors specifically to achieve this. Good sites will shorten ped crossing times from cameras that detect when a pedestrian has hit the crossing button but then buggered off and cameras to detect when the peds have cleared the road.

You can soon tell when the controller has had a full reset of its timing parameters as chaos usually reigns.

However, much traffic light kit is 20+ years old and councils are loathe to rip them out and replace them until they really, really, really can't be kept going any longer. I have a friend who maintains TLs and he has a nightmare keeping some sites going where the only controller card spares are nearly as old as the installation and they can't be guaranteed to be unused, or even working.

[ARW]

I had an odd traffic light sequence in Sheffield one morning a few months ago. The lights on that "ring road" must have manual control.

I was waiting at these lights and the lights seemed to be stuck on red.

Lots of traffic came the other way and then there was nothing in either direction.

After waiting over 4 minutes I said to the apprentice "f*ck this for a game of soldiers, the lights are f***ed I'll jump them".

Just as I set off an armed police unit came in the opposite direction at some speed and blocked me off. He was followed by a big police escort and a prisoner van.

[Nightjar]

Probably a traffic light prioritisation system, which changes lights ahead of an emergency vehicle, in such a way as to clear the route for it.

[ARW]

First time I have seen one in action. Sheffield Crown Court was just up the road.

But clearing both sides of the roads was impressive.

[Andy Burns]

I don't know about Sheffield, but in Nottingham the main firestations have greenwave controllers installed for that reason, the crews can press buttons on the way out the door to clear routes in the required direction, some of these were certainly installed before 2009.

[Tim Watts]

The real question, is who the f*ck was the bastard in the van?

[Dave Liquorice]

Experience?

Well they screwed up the sequencing on a couple of fairly recently revamped light controlled major round abouts near here. Say you are leaving at the 3rd exit, the chances are you'll get stopped at the entry road, as those turn green the exit 1 set will start to turn red, you get stopped there, to watch the green exit 2 set start to turn red as exit 1 set turns green, do I have to say what happens at the exit 3 set...

There are few "green wave" sets about but not many. The only ones I can immediatly think of are along a short bit of the East Lancs Road on the outskirts of Liverpool. Wonderful if you know, first set goes green, gently accelerate to 30 and the next three or four sets turn green as you approach. Of course this doesn't stop people doing racing starts, screeching to a halt 200 yds later, as the lights turn green, so they do another racing start, screech to halt etc etc...

[damduck-egg]

I was told by Dad circa 1958 -1960when I was young that the traffic lights on the Great West Road out past all the art deco factories and past a young Heathrow airport worked on a similar system . A few years back when reading about the road and the area ISTR finding out that 40mph limits were put in place on that section of road around then, before the options were non at all or 30mph so possibly it was done as a way of convincing drivers to drive around the new 40 limit.

Dad has long gone so I cannot ask him how he learnt this or where from.

G.Harman

[edgariredale]

Bath Road at Slough Trading Estate had 30mph linked traffic lights for some years in the late '50s to early '60s.

Edgar

[Brian Gaff]

Its certainly dangerous for pedestrians who cannot see, who rely on the 'spinning dolly' rotating cone on the bottom of the push button box as they have to let go to walk across the crossing. Mind you I think it is still not legal to go if pedestrians are still on the crossing, but that seems not to dissuade some drivers. I have a feeling that in the UK we are a lot less rule following than in, say Germany and hence solutions that work in one place do not work everywhere in the world. Further complications have been brought about for the misguided prioritisation of pedal cycles, which is the only vehicle you can go into a shop and purchase with no warning device or lights fitted and ride with no training or knowledge of the highway code or insurance. Brian

[Nightjar]

...

Which makes it all the more likely that they have a system in place for the transport of priority prisoners. You were lucky they didn't decide that you moving off against the red was part of an attempt to intercept the convoy :-)

However, your experience suggests that, when the lights are prioritised, there should be something to warn other road users that the lights have been set to make way for an emergency vehicle and may stay red for a longer time than usual; perhaps a flashing blue light on the traffic lights or having the red light flash.

[Nightjar]

What about Class 2 mobility scooters?

[Robin]

The way cycle lanes in London and some other places have been installed with bus stop bypasses ((where the cycle path runs between pavements and bus stops) without any form of pedestrian-priority crossing illustrates nicely the way planners seem to have embraced "2 wheels best, no wheels bad". The whole point of these bypasses is to facilitate high speed cycling so the cyclists aren't required or expected to stop for pedestrians getting on or off the bus. I hope you have a DIY solution - if only a "long cane" which cushions your hand from the shock when it is inserted between spokes.

[Adam Funk]

I've seen countdown timers in some other places & drivers seem to use them to gauge how much extra time they have to run the red lights!

[Big Les Wade]

There was a green wave on Camden Street southbound in the late 1970s at least, possibly earlier. Only worked if you kept to 26mph :)

[Chris J Dixon]

Yes, those escorts can be a bit twitchy. A good many years ago, I used to have to pick someone up at Southfields College, Leicester, which is at the centre of what functions as a very large roundabout. Leaving the site was always tricky, so if you saw the road was clear, you didn't hang about.

One night the road closure for the return trip to the nearby prison happened after I had entered. My exit apparently synchronised with the prison van rounding the corner, and I had an unmarked car across my bows very fast indeed. I wonder who would have paid if I hadn't stopped in time?

Chris

[Dave Plowman (News)]

ISTR in London traffic lights on main roads were set deliberately to slow down the traffic speed by as much as possible. For the same reason as speed humps, etc.

[Scott M]

That's sort of my point[1]. UK TL controllers aren't in the dark ages - but if the powers that be wish to inflict misery by programming them a certain way then they can!

[1] I must admit I thought the OP green wave thing was just part of a general moan that we have backward kit!