Get Detected by Loop Detectors

If you have ever been the only person stopped at an traffic light while on your bike, then you have probably wondered if the traffic signal will detect your bike in the same way that it can detect cars. Should you wait it out? Dismount and push the pedestrian button? Or, *gasp* cross through the red light?

While it might seem like the quickest and easiest way out, please never run the red light. Crossing through the red light is extremely hazardous. It is also illegal, and the same hefty fine associated with vehicles applies to bicycles. So, just don’t do it.

You have two options. The first is that you can dismount and push the pedestrian button. This will ensure that the signal recognizes your presence and changes accordingly. Of course, dismounting and entering the sidewalk may pose a frustrating situation for people on bikes.

So, we want to teach you about the second option, which is to position yourself on the loop detectors in the pavement which signal the light to turn green.

What is a loop detector?

Loop detectors are coils of wire set into the pavement which, after they are electromagnetically triggered, alert traffic lights to change in the direction you are traveling.  There’s a good amount of the hard science on the subject, which you can read more about here.

The takeaway is this: putting your bicycle over a loop detector should make the light change faster.

It’s not the weight, it’s the magnetic field

Interestingly, it’s not the weight of the bicycle that trips the loop detector, it’s the metal in your bicycle interacting with the electricity running through the loop detector.  This does mean, unfortunately, that carbon-fiber bicycles may not have enough metal to set off loop detectors.  Since 2007, California state law (with the passage of AB 1581) requires all new loop detectors to be sensitive enough to pick up bicycles.  Bicycle detection at intersections is also now part of the CA MUTCD, contained in Part 4 (pages 67-68 & 88-90) and Part 9 (pages 32 & 44).

The City of Los Angeles uses circular loop detectors. The majority of signalized intersections in Los Angeles are controlled and monitored by a centralized control center called ATSAC (Automated Traffic Surveillance and Control). ATSAC provides real-time monitoring and adjustment of signal timing via over 20,000 loop detectors across the city.

How should people position their bike on loops or sensor areas to assure the best detection?

Detection in an automobile is effortless due to the vehicle’s size. However, because bicycles are much smaller, loop detectors cannot detect the bicycle without correct placement on the loop. It is key to have your bike on the outside of the loop and not in the middle, as shown below. If your bike is perpendicular to the loops, the electromagnetic signal may not be disrupted enough to trigger the signal.

The best place to put your bike at an intersection is directly over the right or left edge of the loop.

The best place to put your bike at an intersection is directly over the right or left edge of the loop.

Often, there will be an additional diagonal slash through the loop detector adjacent to the “limit line” (the edge of the intersection). This diagonal stripe makes it easier for the loop to detect bikes, so you should position yourself directly over the center of the loop and over the stripe, as shown in the graphic below.

Place your bike over the slash in the center of the loop.

Place your bike over the slash in the center of the loop.

How long should a person expect to wait for a signal to respond to their call?

One signal cycle should be enough for the bike to be detected. If more than one signal cycle passes, try rearranging your bike over the loop to maintain the proper placement.

What if there are multiple overlapping loops?

In addition to the loops at the intersection, you might find loops leading up to the intersection and even in the middle of the intersection. These loops detect vehicles in order to best time the green signal during off-peak hours. These loops will likely not be able to pick up your bike as you are passing over them, so focus on placing your bike over the loops at the intersection when you are stopped.

Why do some signals seem to be responsive at some times but not at other times?

It is generally based on the sensitivity. The amount of metal in the bicycle makes a difference, too. If you are riding a heavier bike that has more metal, it will be more likely to be detected by the loop. Accurate placement of the bicycle on the loops is really important. Proximity of cars waiting can also help trip the loop as you wait on your bike, because cars have a lot of metal.

Report Bad Loops

There aren’t many things more annoying than rolling your bike onto a loop detector and getting no response from the light.  If you come across any broken loop detectors, report them to LADOT and we’ll come out to fix or adjust them. Remember that the length of time between signal changes varies, so be certain the loop isn’t functioning before reporting it.

Please let us know about dysfunctional loops by reporting them to 311. Submit a 311 service request online or through the MyLA311 app on your phone. Or, you can also dial 3-1-1 within the City of Los Angeles or send an email to

MyLA311 is an awesome service that you can use to report issues like pothole repair, special item pick-up, and vegetation obstruction. It also provides information about public meeting schedules, events, voting, and contact information for City departments. If you haven’t already downloaded the app, do it now and then tell your friends about it!

[Editor’s Note]: This post was originally published in November 2010 and was revamped and updated for accuracy and comprehensiveness in January 2017.

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