UKC

As part of my early morning commute. I come up against a few things on approach to lights. you know the things, squares sawn into the road.

None of them are very keen to detect my Bike or in frustration me jumping on them.

Questions, How do they work? (magnetic or electrical?) How can I get them to trigger?

In reply to goldmember:
They work by magnetic induction
https://en.wikipedia.org/wiki/Electromagnetic_induction

Basicley the square in the road is an loop of wire than senses any changes in the magnetic field around it. Ferris metals (steel, iron etc) will have a in built magnetic field that causes a current to flow in the aerial.

So the best way is to buy a steel bike.

In reply to goldmember:

More useful explanation: https://en.wikipedia.org/wiki/Induction_loop

I have the same problem with one particular set near my home on my carbon road bike...

Is there a method of triggering if my bike fails to do so?

In reply to goldmember:
They may not be sensitive enough but try experimenting.

We found riding in the gutter and then turning across the sensor opens the parking barrier at work.

In reply to goldmember:

You could try sticking a couple of strong ceramic magnets to the bottom of the frame. Don't know if it would generate the right sort of signal though.

In reply to goldmember:

There seems to be some debate if they can be triggered by a magnet.
http://www.wikihow.com/Trigger-Green-Traffic-Lights

I know for a while the mountain rescue base that is in the yard of the police station used to have "the wheel of freedom". Which was an old spare wheel off one of the vans that had to be wheeled into the middle of the yard to open the vehicle gate so you could leave as the police in their wisdom had installed a new swipe pedestrian access gate but not given any team members a card.

In reply to goldmember:

It also depends on the control software as to whether being detected will help you an awful lot. Some of the older systems for isolated junctions only work by extending green time if traffic keeps coming, being detected at a red with this type of system won't help you at all. The wide-area systems can be so complex that you would be unlikely to notice any difference as an individual if you were detected or not - they are designed to optimise flows in the whole area not just go green on demand.

I have a vague recollection that there are cyclist detectors available but I imagine they'd only be deployed where cyclists are segregated from other traffic and have their own signals.

In reply to goldmember:

A group of ten of us got stuck at a T-junction last weekend. In the end we gave up an turned left on red. Not found an answer myself, other than pulling far enough forward to allow a car to park on top of the sensor

In reply to goldmember:

You'd think when building traffic lights you'd make sure each direction got a green every now and then no matter what the sensors say in case the sensors are in some way faulty or you have a bike/small plastic car. Doesn't seem to be the case though...

In reply to Oujmik:

I've searched for these without success. Could you nudge me in the correct direction?

In reply to bigbobbyking:

http://img.diytrade.com/cdimg/1753215/25343980/0/1333763554/children_plasti...

In reply to goldmember

Clearview do sensors that pick up cyclists, but the old ubiquitous induction loops don't unfortunately. Unless you're riding a 200kg iron bicycle.

http://www.clearviewtraffic.com/clearview-traffic/products-golden-river/art...

In reply to RyanOsborne:
a junction near us has just been redone with fancy sensors. OH comes home from night shifts on his motorbike when there's little other traffic and sometimes gets stuck, as the lights don't change for him

In reply to goldmember:

I'm impressed ! no one has made the observation that cyclists don't take any notice of red lights yet. oh

In reply to ceri: There's a set of lights controlling traffic over a little-used, narrow but blind bridge on the outskirts of Edinburgh. Immediately at one of the bridge there is a T junction which is also controlled by the traffic lights. I sat at a red light at the other end of the bridge on my VFR with nothing coming the other way for a full five minutes before plucking up the courage to venture on to the bridge.

That road has red tarmac along each edge, presumably meant to indicate cycle lanes (although there are no lane markings, and there's no signage). Great idea to route cycle lanes along a road with traffic lights that cyclists can't trigger...

As bigbobbyking says, you'd think that lights like that would have a default cycle time just in case the sensor develops a fault.

In reply to Martin W:

If there's no cycle markings it's probably to narrow the road to slow drivers down.

In reply to goldmember:

If you're gnarly and have balls of steel there's never a problem even when riding ones carbon bike, you have to watch out for sparks when cornering hard though.

Cheers

Toby

In reply to MikeSP:

I was under the impression that some of them still worked on pressure and figured I wasn't heavy enough to trip them.

There are some sets around that I avoid if possible, because not even the motorbike triggers them and it can be a long wait for a car to come along.

The set right outside my house are unavoidable and temperamental even for cars

In reply to goldmember:

There's one near me that is so insensitive that it couldn't even detect a big metal Harley Davidson let alone my bike.

In reply to RyanOsborne:

More here:

https://tfl.gov.uk/info-for/media/press-releases/2015/june/new-pioneering-t...

The control software is SCOOT (which falls into the wide-area category). I'm not sure who is making the detectors in this case, but Clearview (mentioned above) are one of the main suppliers for road monitoring technology.

In reply to MikeSP:

> Ferris metals (steel, iron etc) will have a in built magnetic field that causes a current to flow in the aerial.

Is that what they make Ferrous wheels out of?

In reply to goldmember:

A lot of the ones in Bristol detect me, both those with advanced cycle stop areas and those without, although I do have an 80's steel bike. There is one in particular down on the harbourside though in a segregated bus and cycle street which I have to (carefully) jump since waiting for 3+ minutes does nothing.

In reply to LastBoyScout:


That makes me suspicious that you snuck out in the middle of the night and added a remote control switch to it.

In reply to goldmember:
If I understand correctly they work by mutual induction. So a current in the loop causes a changing magnetic field above (and below) it, which causes a small current to be induced in your bike frame. This takes energy from the loop which is detected by the controller.

So to trigger it you need to take more energy. You can do this by increasing your coupling with the loop. The normal experiment in GCSE physics is to use a coil of wire to do this kind of thing. You have a coil, of sorts, in the form of your bike frame.

The more parallel the frame is with the loop the more it will couple. (The more of that magnetic field, which goes roughly up and down, will pass through it and be captured by it). So one possible trick, which I used to to when I rode a diamond frame bike, is to lean your frame towards the side to increase the area of metal seen by the loop.

I can't see fixed stationary magnets interacting with the loop, but if a magnet is moving then it may induce some current in the loop. It won't change its inductance, which is what the sensor is looking for, but the small bit of current may trigger something. It's not something I've thought of trying.

If you are towards the edge of the loop and parallel with one of the wires then the magnetic field is not so much up or down and has more a sideways component. (Think of it going round in circles around the wires, so it's only really up-down in the middle). So an upright frame may couple more with it there, though it will be weaker there which would reduce the effect.)

I ride a recumbent now, which has a seat with a frame which forms a nice loop parallel with the road. It triggers most of them very quickly, but I've had some instances where it has failed.

[Edit:] This image is the best I've found so far of the magnetic field around one of these things. So it seems if you are cycling towards the edge of it then your upright bike may couple more (more of those lines pass through its frame). Or go in the middle and lean the bike over? https://en.wikipedia.org/wiki/Toroidal_inductors_and_transformers#/media/Fi...

In reply to goldmember:

I remember reading a bit about these a while back;

http://www.veloloop.com/

No idea if they're actually available though...

In reply to m0rjc:

There is an induction loop sensor at the exit to the underground car park by where we live, to raise the exit door when a car is detected (Bikes are usually stored elsewhere). The car entry door has a habit of breaking, usually when someone drives into it. So the way to get your car in when this happens is to get a sturdy bike, go through the pedestrian gate with it, and lay it on the ground by the sensor (just parking it above won't always trigger), watch the gate come up, run back, and drive your car in carefully through the exit lane while avoiding running over the bike. Utterly routine now. We can spectate from our living room and watch someone failing with a fancy pants bike.

In reply to goldmember:

Where there's traffic it's usually sufficient to move forward and ask the driver behind to move forward over the loop. Where there isn't traffic it's usually quicker to get off and walk over the junction or even ride if there's nobody in the immediate area.

In reply to m0rjc:

so... would a small copper coil under one pedal help, and mebbe pedal backwards while crossing the sensor...

In reply to Gone:

Rather than fetching an old bike and then trying to avoid it, would it not be easier to get a steel bar / tire leaver that you can keep in the boot and then just drive over the top of and retrieve?

In reply to m0rjc:

Excellent point, I really should have thought of that as it explains what triggers the car park barrier at work.