Safe Speed Forums

What is the purpose of traffic lights?

I have my own answer which I will mention later (probably when I realise nobody is responding ), but I thought I'd ask the questilon and see what discussions follow.

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Andrew.

Funnily enough... Anyone from Belfast might know where I'm talking about... This is just an example near me. The traffic lights at Duncrue (coming off the roundabout, going onto the shore road, either direction) are often subject to misfire from riots. This means the lights are often out, for a week or so at a time. This junction is reasonably busy. Funnily enough, when the lights are out of action for the week or so after being damaged, there are no accidents on this area of road. It just shows you that people ARE capable of making good judgements at junctions.

Edit: I should say WERE subject to 'misfire' from riots, thankfully it's been quiet since last September...

Personally I don't mind traffic lights which are sensibly timed... But the junction just outside the area I live in has lights, and they are set at one single phasing thing. Now for some junctions this works, but this is one of the main entrances to a shopping complex. Google's imagery is a bit old, but the junction is correct. http://maps.google.com/?ie=UTF8&t=k&om= ... 4,0.001829

Now the timing is fine for a normal day, when people are working, the amount of time means the road (the a2) flows freely, and the traffic coming down the longwood road is allowed onto the a2/shore road every minute or so (maybe more often). The trouble begins on say, a Friday night, when the volume of traffic sitting outside my housing area, waiting to turn right towards the shopping complex increases. This makes a right turn out of where I live somewhat impossible, but people don't realise this, and you do get people sitting waiting to turn right onto the road, where it would be quicker to turn left and come back along the road (plenty of turning places further down the road). I agree here you DO need lights, this is a busy road (one of the main arterial routes into Belfast avoiding the motorway), but surely they should get the timing right...

On the other hand this junction here http://maps.google.com/?ie=UTF8&t=k&om= ... 4,0.001829

now has a set of traffic lights on it. The lights are totally useless at night or at quiet times of the day, although at busy times they are useful. Why can't they have a set of part time lights? What's so difficult about that.

This roundabout http://maps.google.com/?ie=UTF8&t=k&om= ... 4,0.001829
has a set of part time traffic lights, and I am sure they're an absolute Godsend to people coming down the station road. They are only active from about 7 until 9 or so, they stop the traffic on the Shore road, letting the traffic get off the station road, and into Belfast.

Yet this roundabout http://maps.google.com/?ie=UTF8&t=h&om= ... 4,0.001829
which is only about 3/4 mile from that previous one, at the bottom of the M5 motorway, hasn't got any part time lights, and it could REALLY do with a set. Every evening there is about a mile's tailback on the M5, and if you follow it you'll find that it is part of the M2 motorway, coming out of Belfast.

I'm not too sure who to contact, or even if I should...

So now to answer the question.. Traffic lights are to guide traffic (or to try to) at busy junctions for an extended period of time (so they shouldn't be used for a short term thing). More attention needs to be paid to the density of traffic though, it seems around here that they place the lights and just ignore them...

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Mike

I would define that in general terms the purpose of traffic lights is to manage traffic, but perhaps to be more specific their purpose is to stop traffic <for whatever reason>.

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CSCP Latin for beginners...
Ticketo ergo sum : I scam therefore I am!

I would say that these days, traffic lights are for creating congestion and frustrating drivers.

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Pecunia Prius Equitas et Salus

I think traffic lights ration contested road space.

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Paul Smith
Our scrap speed cameras petition got over 28,000 sigs
The Safe Speed campaign demands a return to intelligent road safety

I'd go with the "manage traffic" as an overall aim, but in specific cases they do different things:

Motorway slip road lights: There to annoy drivers, and to ensure that every driver has to accelerate at maximum possible revs thereby pushing out maximum fumes and pollutants in order to join the motorway without causing an almighty pile up.

Gathurst Railway Bridge lights: There to allow drivers to go through without having other cars trying to come the other way (it's a one car wide bridge on a bend, so lights are the only solution but they have sensors that work so if there is no traffic in the other direction they change to allow you to go through very quickly)

Pelican Crossings: Only required if zebra crossings don't work, surely?

Sometimes lights work better than roundabouts, sometimes roundabouts work better than lights. Lights on roundabouts are a fiendish plan to make the ability to merge in moving traffic a skill long forgotten by UK drivers (ditto motorway ramp lights, which are an abomination)

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COAST Not just somewhere to keep a beach.

A young loner on a crusade to champion the cause of the innocent, the helpless, the powerless, in a world of criminals who operate above the law.

To give local authority highway engineers something to stick on a roundabout?

Sorry I was being flippant.

Having read paul's post elsewhere about give way lines v traffic lights I would say that traffic lights are for when other engineering measures fail! A kind of last resort, usually resulting from cost/land issues.

Original use: To manage traffic and allow vehicles to cross and merge safely and efficiently in busy conditions.

Current use: To frustrate drivers, slow them down and create congestion in order to make driving as miserable an experience as possible and create an excuse for satellite spies

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Why can't we just use Common Sense?

Traffic lights are now a first resort traffic management tool to regulate two or more at grade roads that are required to intersect.

I've always thought that in the majority of cases roundabouts are preferable, even mini-ones because there is no idle time. Previously I've even proposed a 4 way Give Way at cross roads where no-one has priority which I believe has been successfully implemented abroad.

At very busy intersections then a grade seperated junction should be considered if a case can be made for it and the space and other practicalities allow it. Only as a last resort should traffic light be chosen and then they should be intelligent ones able to adapt and change to give the optimum flow for each road at a given time. Do these exist?

Ooh, good topic.

One of my pet irritations is hearing people complaining and throwing their hands up in horror whenever anyone dares to suggest jumping a red light.

Obviously when there are other road users around, then obeying the protocols is the way to go.

But what about when the area is clear and visibility is good?
This is one reason I dislike red-light cameras, safety issues are not considered, only legal compliance for the sake of it.

I put it in the same league as:
- staying in the middle lane of the motorway when no other traffic is affected
- crossing the road with a "red-man" when the road is otherwise deserted (a fineable offence in the Netherlands).

At least many of the lights in the Netherlands flash amber late at night, meaning "proceed carefully everbody, observing rights of way".

I agree that roundabouts are preferable. What I don't understand is the recent infatuation with sticking lights ON roundabouts? When did this start happening and is there any proof to show it reduces congestion or accidents? If it reduces accidents on the actual roundabout does it lead to an increase in accidents on the approaches to the roundabout? And what about accident severity?

There are two large roundabouts near me which had lights installed in the last 2 years. Previously there was little to no congestion but ever since the day they activated the lights on the roundabouts there are massive tailbacks on every approach. I've since started using a longer route to work just so I can avoid the roundabouts. Previously the roundabouts always seemed to work excellently and never really had any congestion.

What is the logic behind the roundabout/traffic lights combo?

"To improve the flow of trafffic" is my answer. All traffic, even pedestrians.

Part time traffic lights on roundabouts sometimes might help. Perminant ones encourage people to ignore them.

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Andrew.

You want to drive/ride around West Bromwich...

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Pecunia Prius Equitas et Salus

I'll state the obviously cynical answer... to encourage people to burn up more fuel and thus increase the government's revenue from tax.

I mean that's what they should be used for.
It's the same in Poole at night. Or in the evenings. Or any time except maybe during rush hour (when I don't drive anyway). There is a junction which was a give way, now it has traffic lights. Waiting for them gets very frustrating because you can see there is nothing coming the other way (and there is only one 'other way')
Then there's the Fleets Bridge 'roundabout'.
These lights don't demand respect and... err... don't get it.

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Andrew.

Anyone around Teesside will know the Marton crawl, (45mins to do 3 miles at peak times), which has been exacerbated by replacing a roundabout with traffic lights .

Traffic news this morning 'Marton crossroads traffic lights are not working, but traffic seems to be travelling quicker than normal, with no reports of any accidents or delays'

WTF?

That sounds good! It's always nice when there's a power cut here actually, people CAN negeotiate junctions, why do the government assume traffic lights are ALWAYS required... I guess it's the same as speed cameras though.

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Mike

Here in Crewe we now 'enjoy' two signalled roundabouts on our way to and from work living on the east side of Crewe. Known locally as 'Death by Traffic Lights' they have been installed to improve traffic flows at peak periods. (there are lots of other new lights as well, in fact there are now 12 to be negotiated in about a mile and a half)) This is because a roundabout only works if traffic seeking entrance to the roundabout is balanced, but in this case it is not, and previously, large queues built up on the main road into/out of town.

Unfortunately these kind of roundabouts can only work if there is free exit from the roundabout; if this is not so, as at the Crewe Arms Hotel near the station, the roundabout locks up as those prevented from leaving block the other exits.

There is also absolutely nothing at all about signalled roundabouts in the Highway Code, eventhe new edition. The usual supine Department of Transport, I really do wonder what they do all day in their Marsham Street offices in London. Not very much I'll bet

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Good manners maketh a good motorist

The purpose of a traffic light should be to ensure that there is no "starvation" in what is effectively a queueing system for a resource.

In a situation where one branch has permanent priority, the other branch can easily be starved out, i.e. you could be waiting in theory forever to enter a roundabout if there is no phase where traffic already on the roundabout has to let you out.

They introduced the traffic lights on the White Hart Roundabout in Northolt in 1996. I used that road every day at that point, and the moment the lights were introduced the f;pw on the northbound A312 approach was a lot faster. At the time the Egham Roundabout (A30/A316 junction) desperately needed one too for the approaching Eastbound A30.

The problem is that lights are not phased correctly - on the whole the phasing should favour the major road over the minor one. So the A10 Kingsland Road should have a longer green phase than the roads it crosses, particularly the unclassified ones. I can say that having used that road that is not the case - even on my bicycle I avoid that route at all costs and use the unclassified route of Stamford Road / De Bouverie Road etc. which has only one traffic light (crossing Downham Road) and that one is phased for a reasonably fast turnaround.

Signalled pedestrian crossings are actually better for road traffic in theory than zebra crossings, as on a zebra crossing it is the road traffic that can suffer "starvation". Berkeley Square (Conduit Street junction) and Great Marlborough Street (near Carnaby Street) are examples of this. (Both of them in W1 postcode, both inside the CC zone too).

One of the problems is that it is sometimes more "dangerous" to enter or cross a main road than a side road, so the main roads are often littered with traffic lights whereas the "rat-runs" are not. This of course encourages rat-running (even in a car - cyclists are encouraged to use rat-runs).