I have just come to the USA (Bay Area) and got a bicycle to commute to my university. Being new to this place I kept wondering why sometimes I have to wait for a long time for a green light to make a left turn, and then a car comes along and the signal switches to green in ten seconds. Today I waited for a green light for five minutes and it did not come, since there were no cars in my lane. I started thinking I was insane, but then found this: How do Traffic Lights Notice Bicyclists? Sure enough, there are cameras in the intersection.

So how do people deal with this? Wait for a car? Turn on the red light? Use the pedestrian style of making left turns? Wave to the camera?

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    In the Bay Area (at least my part of it) there are often painted marks where you're encouraged to stop, something like bikelaw.files.wordpress.com/2009/05/bs_loop.jpg - and in my experience, a lot of the loops in car lanes are double loops, and the mark's at the front of the center line. You can usually see the cuts in the road, kind of like a very tall OO smashed together. I can almost always manage to trigger lights. See also the top half of this image: austincycling.org/webfm_send/114
    – Cascabel
    Commented Oct 10, 2011 at 6:40
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    If it uses a magnetic loop to detect vehicles your best bet is to glue a small strong magnet under your bike, here in the netherlands it is often used on carbon bikes
    – HTDutchy
    Commented Oct 10, 2011 at 9:01
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    @s4uadmin: Those loops being magnetic is a common misconception. They're inductance coils and anything close to them that conducts electricity can be picked up. Any metal on the bottom of the bike can help.
    – freiheit
    Commented Oct 10, 2011 at 18:39
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    They're upside-down metal detectors. Instead of you holding a metal detector on a pole looking for a lucrative bit of treasure buried in beach sand, it's the detector that buried, and your bike/car/whatever is the object to be detected. You just need a detectably large piece of metal on the vehicle.
    – DarenW
    Commented Oct 10, 2011 at 19:23
  • Another option would be to trigger the pedestrian walk button.
    – miguel
    Commented Oct 19, 2011 at 22:50

5 Answers 5


In most states it's the law that if the signal is malfunctioning you can proceed through "with caution" against the signal. Forester and others have argued that if a signal does not appropriately recognize the presence of a bike it's "malfunctioning" and you're on reasonably firm legal ground to invoke the "malfunctioning signal" provision. (However, I've never heard of this being tested in court.)

Do note that the presence of a camera does not necessarily mean that the signal is video-controlled. It may be that the cameras are there for general traffic monitoring, and the signal is still triggered by buried loop, radar detector, etc. Also, often there are sensors installed for detecting oncoming emergency vehicles that look a little like a camera but are not.

If it is a buried loop you can usually tell by observing the cuts in the pavement where the loop was installed (though of course a buried loop may be subsequently converted to video control). But with a buried loop the best place for the bike, to optimize detection, is more or less directly over one side of the loop, vs being in the middle of the loop. (As a last resort, lay your bike down over one side of the loop. I used to deal with one intersection where I could trigger the signal by just leaning the bike to about 45 degrees.) Note that a steel bike will usually be more effective than an aluminum one, and a carbon fiber bike is unlikely to be detected at all.

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    Heres an example for Virginia dmv.virginia.gov/exec/notice.asp?id=113 Motorcycles, mopeds and bicycles may treat a red light as a stop sign if their bike fails to trigger the traffic light and they are stopped for two complete cycles of the traffic light or for two minutes, whichever is shorter, and they yield the right of way to any approaching vehicle from either direction.
    – Jacob
    Commented Oct 10, 2011 at 2:32
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    Thanks for the Forester ref - every red-light jumping cyclist should know this 'malfunctioning' line of argument just in case some policeman asks why they brazenly went through a red light. Commented Oct 10, 2011 at 9:38
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    In the UK, I believe the correct action to take when faced with a malfunctioning signal is to turn around and find another route.
    – Skizz
    Commented Oct 10, 2011 at 12:35
  • The note about leaning your bike is very good and important: These induction loops do not so much detect metal, they detect horizontal area around which electrical current can flow. A perfectly vertical bike does not provide much of that area, as the area is only as wide as its metal tubes. A leaned bike, however, registers the area inside its wheels (unless you have carbon rims) and inside your frame triangles (unless you have a Y-frame or carbon frame). For metal diamond frames, leaning is very effective. Commented Jan 1, 2021 at 21:42
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    @DanielRHicks: Not on the road, they have to be on the footpath. Everthing has to stop at the solid line when the light is red - the line ends at the kerb so pedestrians and cyclists on foot can still pass the light when it's red as they're not crossing the white line.
    – Skizz
    Commented Jan 3, 2021 at 15:28

Cameras can also be red light cameras. Loops detectors can have smooth pavement. You may be able to figure out which cameras are definitely for signal control, though. I know in my area it's a very different style of camera placed in a different location than the red-light and emergency vehicle priority detection cameras.

Assuming it is a camera-controlled intersection:

  • If there's a little cycle symbol with lines put your tires on the lines. That's where the system is looking for a bicycle.
  • Be in the center of the lane, not the edge. The cameras are looking in a specific area for each lane, and if you're at the edge you might not register at all. Be where the camera is looking for a car.
  • Be bigger. Wave your arms. Take off your jacket and wave that. If you have a light, shine that up at the camera.

If none of that works, depending on the exact details:

  • If green for straight:
    • go straight through the intersection, pull over at curb and push pedestrian signal
    • go straight partway through the intersection, pull into the crosswalk on the right and flip your bike 90 degrees so that you're now at the front of the appropriate going straight lane for the direction you originally would've turned into. Smile and wave cheerfully at the confused car driver that's now behind you. (it's a "box turn")
  • If red for straight:
    • Right curb is easier/safer (can see cars behind you), so go over to right curb. Push both pedestrian signals and do the pedestrian 2-crossing left turn or a pedestrian style box turn
    • If you can see any potential directions somebody would turn into the oncoming lane, you can go across to the left curb, in which case you should be able to just push one pedestrian button and start pedaling off when you're most of the way across in the crosswalk.
  • If you're feeling brave and everything is totally clear for miles: proceed through the light (after stopping). I didn't bother digging up the exact california law, but the california driver's handbook basically says a malfunctioning signal should be treated like a 4-way stop. The part where the signal is only malfunctioning for one specific lane isn't really well-covered, though.

If a signal isn't picking you up, it's malfunctioning and needs to be fixed. It's a hazard. Note the exact location, day of week and time of day, and report the hazard.

You didn't say exactly where in the bay area you are. However, East Bay Bicycle Coalition and Sonoma County Bicycle Coalition have hazard reporting systems on their sites. Silicon Valley Bicycle Coalition and Marin County Bicycle Coalition have guides to help you figure out who to call.

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    Disclaimer: I'm on the board of the Sonoma County Bicycle Coalition.
    – freiheit
    Commented Oct 10, 2011 at 3:35

From http://www.ecovelo.info/2010/06/17/trigger-happy/ (written by Alan Barnard):

"You can often see evidence of loop detectors as lines cut into the road surface just behind the crosswalk. Wire sensors are embedded in these cut lines, and it’s possible to trigger a light by placing your bicycle wheels precisely on top of one of the wires to disrupt the magnetic field. Some sensors seem to be more sensitive than others; in those cases where the light isn’t initially triggered, I’ve had some success by leaning my bike over toward the inside of the detector loop. In cases where there are two side-by-side loops, lining up over the center where the two loops meet doubles your chances of triggering the light. Once I understood exactly how loop detectors work, my rate of success at triggering lights considerably improved; I’m currently getting somewhere approaching a 90% success rate on the detectors where I live."

There are a lot of interesting comments there, also!

Hope it helps


After using the other advices, to help yourself, you should inform the authorities about the malfunctioning, nonfunctioning device.

Think about other cyclists, which don't know what to do as well.

Can it be, that street planning is done without modern bicycles in mind? If an accident occurs, they shall feel guilty! But better: They should rework their technique, and choose another approach.

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    I would say to inform them anyways. I had a intersection that wasn't working right a few years back and I called the city. They sent a guy out the next week to tweak it. The light triggers now reliably. .
    – BPugh
    Commented Mar 20, 2014 at 13:28

In L.A. you have visible coils in the asphalt to detect metal. it's used for red lights and traffic detection. enter image description here
(source: instructables.com)

on the bike lanes, there's smaller ones that are able to detect bikes.

when there's only the regular lanes, it will never detect a bike. what i do is if there's a car behind me, i stop on the pedestrian crossing area and hope the car will move forward and trigger the damn thing.

if there's no hope of that and i know it's one of the two take-forever-red-lights in my path, i just go directly to the pedestrian button on the side walk.

... scratch all that! just found a solution when looking for a picture to put here!


solution: magnets under the bike!

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    Can anyone attest to whether these magnets work as intended?
    – r00fus
    Commented Oct 27, 2011 at 5:43
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    well, it's a coil with a simple field. if the coil is intended for cars, any magnet that distort a magnetic field the same amount as 1TON of steel would work. it's common sense that magnets distort magnetics field more then plain metal. but i have no idea how to conduct the experiment to see how much more.
    – gcb
    Commented Oct 27, 2011 at 22:57
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    Actually, the pick-up coils detect the presence of a vehicle by the way it changes the coil characteristics. This is a function of the mass of the metal and its reluctance and ferromagnetic properties. A magnet, unless moving (fairly rapidly), would have essentially no effect. Commented Mar 20, 2012 at 11:57
  • @DanielRHicks Not mass. Horizontal area enclosed by electrical conductors. If you put down a loop of copper wire that matches the shape of a single induction coil, you'll pretty much get maximum detection signal. (Btw, those 8-shaped double coils in the images should perfectly detect bike on their center line. The magnetic field of these coils is horizontal above the center conductor, perfectly positioned to detect the rims and frame triangles of the bike. It's the single coil lights that may fail to detect a bike in their center. Which you can still trigger by leaning your bike to the side.) Commented Jan 1, 2021 at 22:44
  • Can the sensors detect a carbon bike with carbon wheels? I imagine your body also messes with the magnetic field, but I'm curious. Commented Sep 28, 2023 at 17:38

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