Activating traffic lights

mikemac

I'm no engineer, can you maybe explain this to me

I do cycle on my route (Dublin), Ballyfermot to IFSC.
When you leave Ballyfermot you arrive at Chapelizod Bypass, a busy road with plently of fast moving traffic.

Many times, I've been there at 6am on the way to work waiting, waiting and waiting for traffic lights to activate.
Car pulls up behind me and instantly the cycle starts.

How does it work, is there a sensor somewhere?
Let me also say I ride a scooter too and have the same issue here. And at one other junction that I can think of.

Traffic flies along that road. But if I break a light and something happens, if I'm not killed, I'll be at fault. At this junction you can't see all traffic lanes due a hedge so with the speed they go it, it's not safe to break it

Any other junctions like this?

Micilin Muc

I'm no engineer either, but I've noticed at other junctions how there is sometimes four square or two squares on the tarmac just before the white line. I roll over all square if there are no cars around and that usually activates the lights.

Keep an eye out for them next time.

tawfeeredux

I know that junction but have never been stopped at it without a line of traffic coming from Ballyfermot direction stopped there also. It could be that the sensors at the junction are calibrated to only set off the sequence when there's a number of cars backed up, maybe there's a sensor a few yards back from the junction. I know on some junctions around Lucan, i can set off the sequence on the bike, but I presume that's only because they're relatively minor junctions.

markpb

Like Micilin Muc says, there are loops embedded in the road around the stop line. They pick up the magnetic disturbance caused by metal above them and tell the traffic light controller to change the lights (usually at the end of the next cycle, not immediately). If your bike doesn't have much metal in it, you won't activate it. Likewise, if a construction company dug up the road and damaged the wires, nothing will activate it and it'll never go green or it will fall back to a (usually very slow) timer.

If you can't find the loop, look above the traffic lights - there could be a sensor above it which does the same job as the loops. I'm not sure how it works though.

Moflojo

http://auto.howstuffworks.com/car-driving-safety/safety-regulatory-devices/question234.htm

vektarman

feelingstressed wrote: »

I'm no engineer, can you maybe explain this to me

I do cycle on my route (Dublin), Ballyfermot to IFSC.
When you leave Ballyfermot you arrive at Chapelizod Bypass, a busy road with plently of fast moving traffic.

Many times, I've been there at 6am on the way to work waiting, waiting and waiting for traffic lights to activate.
Car pulls up behind me and instantly the cycle starts.

How does it work, is there a sensor somewhere?
Let me also say I ride a scooter too and have the same issue here. And at one other junction that I can think of.

Traffic flies along that road. But if I break a light and something happens, if I'm not killed, I'll be at fault. At this junction you can't see all traffic lanes due a hedge so with the speed they go it, it's not safe to break it

Any other junctions like this?

Is that the junction at Vinny Byrnes as the Kennelsfort road meets the N4?

This may have been mentioned, or something similar, AFAIK the lights react to a pressure sensor under the surface, if the scooter doesn't activate the lights, let alone the bike, the local council will need to adjust the sensor sensitivity.
Edit: Explained in other posts

poochiem

http://www.youtube.com/watch?v=Sj-mNB6dLkk

FISMA

There are several different versions: mass, metal, ... I even think some are tripped by emergency strobe lights.

Anyhow, we have all seen those loops in the ground - they are the most familiar ones.

This may not work with a bike, or at all, however if/when it does, it is fun to know.

You're driving down the road and coming to a light when you see the first box, a second, and then the final third box. You've crossed #1 and 2 and the light now knows you are on #3, it may wait until #2 and #1 are filled by other cars until it trips the light. So........

If you were to reverse back over the other two, the light will think they have been tripped, resulting in a green light. :mad::):D

No civil engineers on the board today?

Note: that I did not say that you should reverse, nor am I encouraging such behavior.

Where I am the sensors go by mass so riding back over them does not help.

Also, my carbon ride does not offer much in the line for E&M Lenz's law kind of stuff. I have heard that sometimes you need to angle your bicycle by the sensor, if we are talking the E&M type.

Hope that helps, I told a friend about this once and he thanked me for saving him 5 minutes of his life every day.

Is there a button to push? If they are not used too much, that usually works for me.

CramCycle

Micilin Muc wrote: »

I'm no engineer either, but I've noticed at other junctions how there is sometimes four square or two squares on the tarmac just before the white line. I roll over all square if there are no cars around and that usually activates the lights.

Keep an eye out for them next time.

Magnetic coil that reacts to the metal on your bike, some are slightly to deep and also carbon bikes struggle to set them off

poochiem wrote: »

http://www.youtube.com/watch?v=Sj-mNB6dLkk

Great explanation.


There was another thread on here before about this but I can't find it. In cases where your bike does not set off the sensor, or it is clear that the loop is not including your lane of traffic to let you move through, I believe you are allowed to move through with caution as it can be referred to as a stalled light, which AFAIK are allowed to be passed through akin to a yellow light. I think you are expected to wait a few minutes (not really clear to me) before attempting to pass. Or like the youtube video says, dismount and hit the crosswalk button. It is worth notifying loops that are not set off by at the very least a steel frame bike to your local councillor/council. My bike sets off most but there is one on the way home that is problematic. I wait a few minutes and hope for a car or a Garda (its near the american embassy, so usually close) and ask can I move through (they normally think I am a tool) but I guarantee the first night I run it, I will be taken off my bike as I have seen the daytime garda around there doing it to cyclists.

mikemac

vektarman wrote: »

Is that the junction at Vinny Byrnes as the Kennelsfort road meets the N4?

Oh no, not out that far.
It where you come up a hill past the GAA club as you exit Ballyfermot onto Chapelizod bypass
No nearby pedestrian crossing, that's a few hundreds metres down the road

poochiem wrote: »

http://www.youtube.com/watch?v=Sj-mNB6dLkk

Quality video! Informative and pretty witty too.

Thread has been informative, thanks all.

I'll take a spin up and see it I can see any markings