On a current thread there is a discussion about temporary traffic lights, which has included mention of sensors.
It reminded me of something happened a few weeks ago when I was waiting at some lights at the junction of minor road and a dual carriageway (I was on the minor road).
For some reason, I stopped quite few feet away from the stop line, and then waited for what seemed a very long time (I have used the same lights a few times before and since and have never waited anywhere near that long).
I must admit that it was the missus who finally mentioned the box/camera attached to the lights and asked if it was a sensor. I moved forward a few feet, and the lights changed almost immediately.
Was it coincidence, or do such lights require a sensor to be activated, before changing?
It's never occurred to me in the past, probably because I've never stopped that short of the line before.
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>> do such lights require a sensor to be activated, before changing?
Yes.
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Used to be a right pain when I had a moped many moons ago.
A set of traffic lights had road sensors and they would not detect my moped.
As it was a Sunday morning, before Sunday trading was allowed, I had to wait for a car or change my route and as it was a 7AM trip it was easier to change my route.
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Much as I believe that anybody who wishes to work on a Sunday should be allowed to do so, I did used to enjoy the complete deadness of towns on a Sunday morning.
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>> Much as I believe that anybody who wishes to work on a Sunday should be
>> allowed to do so, I did used to enjoy the complete deadness of towns on
>> a Sunday morning.
>>
Me too.
Especially being able to cycle in London on a Sunday morning and hardly coming across a car, and seeing very few even out of town.
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>> Used to be a right pain when I had a moped many moons ago.
>>
>> A set of traffic lights had road sensors and they would not detect my moped.
>>
>>
>> As it was a Sunday morning, before Sunday trading was allowed, I had to wait
>> for a car or change my route and as it was a 7AM trip it
>> was easier to change my route.
>>
I encounter similar problems on the bike but found an alternative solution.
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I used to ride home at very odd hours at one time in my career, my bike wouldn't trip the embedded sensors..I took a pragamtic and common sense approach...
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The boxes on top of lights use microwave detection produced from movements. Their design stems from when new sensors were needed for portable signals. There are a few problems with them, and different to the use of buried wire loops in the approach to the lights, which have precise sensing position.
The detection range of the boxes is a bit too long for efficient traffic control in towns. You don't want lights changing to green when a vehicle is still a hundred yards away. So they are dipped down to curtail their range. There is no alternative inherent range detection mechanism. But you can obtain a rough range measurement for a departing vehicle by counting beats.
Secondly, in order not to trigger them with pedestrians, the low speed movement detection is/was curtailed. That means if you approach lights slowly while waiting for a change, you may not be detected --- if curtailment is still used.
To avoid an undetected vehicle being stuck at lights because another vehicle has not arrived, there is/was a two-ish minute timer in the system that put in a demand (vehicle detection signal) if a real one had not occurred in that time.
Thirdly they suffer from blinding, which the dipping helps overcome. A vehicle departing can put in such a strong signal that the signal from the front of an approaching vehicle is not evident. The 'radars' (not strictly a radar but a convenient word) have direction sense -- embedded in the doppler signals they produce. So both directions are detected in the box, and the unwanted one is suppressed.
Your direction-sensing gatso could measure your approach speed. It does not do that because it does not know when you are on the measuring marks.
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Locally all the railway bridges are being replaced as overhead electrical wires need installing prior to electrification of the main Glasgow-Edinburgh trains.
Bridge I used on a fairly quiet road, say 1 x per week, had excellent traffic lights - both sides showed RED until a car was sensed when they turned green for you.
£2m bridge and new lights - timed 2 minutes then the lights change colour ........so much for progress!
Why lights on a quiet road? 2 way traffic would need a stronger bridge to support the weight of the traffic!
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There is a set of lights near me which is a right turn across a dual carriageway.
It will change for you to cross without stopping - far more often than not - provided you approach as if you are a bus: in a mimsing fashion and decelerating gently to the speed you'd need to take something big across the right turn, over the length of the slip road.
If you hurtle towards them and throw the anchor out at the last nanosecond you always wait. And wait. And wait...
How many other lights are set up like that?
Or is it really just serendipity?
Equally, I'm sure I've heard of some lights that change to stop through traffic, if you are considered to be going too fast...
Last edited by: AnotherJohnH on Wed 7 Aug 13 at 14:43
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There's another theory with temporary lights that if you charge them with your foot down and flash your lights, they will change for you.
A dubious one, I think, unless you believe in catching the Hogwarts Express.
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Dubious I agree, but I thought it was a double flash - to imitate blue lights.
If it works, it would only work when the lights are clear of traffic.
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Years ago,when I worked,we entered our factory via a slip road off a main dual carriageway up to a roundabout..To avoid a tailback onto the road,the council fitted "rush hour traffic lights".These gave priority to the road with most traffic and that was usually coming across the roundabout over the main road and traffic on the slip road could be held for a long time-until someone stopped over the pick-up at the beginning of the slip road so that the box controlling the lights would think the slip road was full and change the lights to green.Most traffic lights still use the coil set in the tarmac.
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If you google "traffic light bus priority" (no quotes) you will find many documents on the subject of bus priority. Such as sending a radio signal to the traffic light controller from the bus.
And buses fitted with equipment such that they are aware of when to send that signal.
I doubt your speed of approach, such a mimicking a bus, gets you any priority.
Decades ago there was talk of having a loop under the bus to put a signal into the road loop, but I don't know if that was ever implemented.
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OOPs. It also looks like I am a bit out of date.
Here is an infra-red one (PIR)
www.geneq.com/catalog/en/ir_200.html
Mounted at a height of 5 metres ! !
Last edited by: busbee on Sat 10 Aug 13 at 08:20
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"And buses fitted with equipment such that they are aware of when to send that signal. "
Here in Nottingham, it's www.scoot-utc.com/BusPriority.php
Most traffic lights also have 3 induction loops in the road on the approach and 'gap detection' loops further up trunk roads. You can make traffic lights change by stopping on these, but it takes trial and error to find how they are programmed. e.g. stopping on loop 3 when loop 1 and 2 are empty sometimes works and other times doesn't until you move forward. We also have the problem of far-left councils using traffic signals to create congestion, so often you may get the opposite of logic/the desired effect.
We used to have the green wave in the UK, until New Labour banned it during the late 1990s*** and gave councils grants to create congestion so that they could set up charging schemes. I think the coalition have reversed that since then
*** en.wikipedia.org/wiki/Green_wave In the UK, in 2009, it was revealed that the Department for Transport had previously discouraged green waves as they reduced fuel usage, and thus less revenue was raised from fuel taxes.[9][10] Despite this government Webtag documents were only updated in 2011. It is still unclear if the economic appraisal software used to apply these guidelines has also been updated and if the new guidelines are being applied to new projects.
gse.cat.org.uk/papers?download=6%3Ablaise-kelly-a-green-wave-reprieve
Last edited by: sooty tailpipes on Sat 10 Aug 13 at 22:33
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>> Dubious I agree, but I thought it was a double flash - to imitate blue lights.
A burst of several quick flashes (perhaps 7 or 8 flicks within 2 seconds) certainly used to achieve this effect on all the lights around Bedford Hospital / County Hall in the dead of night a decade ago.
Last edited by: Dave_TiD on Sat 10 Aug 13 at 22:56
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Traffic light sensors - swiss tony
