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.

0 replies
  1. Alan Thompson
    Alan Thompson says:

    One important note, the law isn’t specific to loop detectors.

    Other means such as video cameras with software able to detect bicycles can also be used (which can also make the act of counting bicyclists for planning purposes much more efficient/cheaper).

    Of course, the loop detectors are already in place, and if they can be tweaked to detect bikes, then that is cheapest of all.

  2. Dennis Hindman
    Dennis Hindman says:

    Hopefully everyone at LADOT bikeways will take a look at and discuss the new Streetsfilm by Clarence Eckerson Jr entitled Portland’s Bike Boulevards Become Neighborhood Greenways

    Except for the odd way of using Sharrows signage it looks like most of these treatments could be used in Los Angeles. Wouldn’t it be great to commonly see whole families riding down streets together? That is a sure sign that bicycle infrastructure gives a sense of safety to all users.

    The use of road signs that give direction to where the highlights are on the main arterials are extremely important to make these side streets valuable to even the experienced cyclists. Without them the neighborhood friendly streets will not get as much support from the fearless bicycle riders.

    Fast, easy to get where you need to go and a feeling of safety are all vital to great a large increase in bicycling modal share.

  3. Eric B
    Eric B says:

    Street-facing push buttons are not an acceptable alternative to in-street loop detectors. They invariably require the bicyclist to hug the curb to reach the button in exactly the place where staying away from the right curb is critical (intersections). Cyclists near the right curb are at serious risk for being right hooked. Cars wishing to turn right will line up to the left of the through-traveling bicyclist, setting up an unnecessary conflict point. Even worse is when cities place the bike push buttons to the right of a right turn lane. I hope that these push buttons are an illustration of what NOT to do rather than a feature on bike friendly streets.

    • ladotbikeblog
      ladotbikeblog says:

      Agreed, Eric. Street-facing push buttons are only really useful at intersections where no right turn is allowed on red. Since this is California, there aren’t many intersections like that.

  4. PlebisPower
    PlebisPower says:

    A recent post on diversions reminds me that there is a real call for a demonstration project in Los Angeles to roll out some of the innovations mentioned here, least being loop detectors that work and stenciled guides. Great ideas too, but let’s think bigger and better. Rolling out a plan for an intersection featuring separated bike circulation with integrated signaling would be a great complement to the adopted bike plan (perhaps in December).

    • ladotbikeblog
      ladotbikeblog says:

      Getting the Bike Plan adopted will go a long way towards achieving that goal. When we can point to those treatments in the Technical Design Manual, we can become eligible for using federal and state funds for the project.


Trackbacks & Pingbacks

  1. […] better than loops sawcut parallel and perpendicular to the direction of travel. The article Anatomy of a Bicycle Friendly Street: Loop Detectors at LADOT Bike Blog has a really good explanation on how to reliably detect bicycles with loop […]

  2. […] If the light is red, be sure to stop behind the limit line (this will position you on-top of a loop detector, which alerts the traffic signal that a bicycle is present). When the train clears and the light […]

  3. […] If the light is red, be sure to stop behind the limit line (this will  position you on-top of a loop detector, which alerts the traffic signal that a bicycle is present). When the train clears and the light […]

  4. […] a roundabout, crosswalks, bulbouts, advanced stop bars, a pedestrian crossing warning device, bike loops, signage, sharrows, bike racks, and some SRTS encouragement programming, as well. These will likely […]

  5. […] of traffic calming devices, Sharrows, road signs, directional signs, traffic circles, chicanes, loop detectors, diverters, […]

  6. […] signals can be activated by a number of different devices including bicycle sensitive loop detectors, microwave detectors, infrared detectors, video detectors, or push buttons. Per the Bike Plan TDH, […]

  7. […] Podaję przykładową stronę internetową, na której można znaleźć informacje o wykorzystaniu pętli indukcyjnych w mieście Portland: oraz w Los Angeles: […]

  8. […] over 3 miles from Cochran Ave to Hoover St. It also has new bike-sensitive loop detectors which can pick up the wheel of a bicycle at each stoplight. If you’re unsure of where to place your bike to activate the signal, check out our previous […]

  9. […] can read our introductory post here. You can also find previous posts on chicanes, round-a-bouts, loop detectors and other BFS treatments […]

  10. […] The “Bundle of Bicycle Friendly
    Streets” and “Bike Friendly Street in a
    Box,” could also be programs that bring long-term change
    by expanding LADOT’s tool box.  The term
    “Bike Friendly Streets” first appeared in the
    2010 Draft Bike Plan as a replacement for Bike Boulevards. 
    However, the plan is unclear what a Bicycle Friendly Street
    actually is, although the LADOT Bike Blog has written about some
    treatments the streets could see such as roundabouts and loop
    detectors. […]

  11. […] This post was mentioned on Twitter by Barbara Hui, Di-Ann Eisnor, The BICYCLE AUTOFEED, Joseph Guisti, the anty and others. the anty said: How to trigger the stop light on your bicycle: […]

  12. […] tips on what to do if you’re in a collision; here’s my take on the same subject. A look at the signal loop detectors that makes a Bike Friendly Street bike friendly. CicLAvia is looking for volunteers for Host […]

  13. […] This post was mentioned on Twitter by Evan G. and Nate Baird, Christopher Kidd. Christopher Kidd said: Anatomy of a Bicycle Friendly Street: Loop Detectors! #BikeLA […]

Leave a Reply

Want to join the discussion?
Feel free to contribute!

Leave a Reply

Your email address will not be published. Required fields are marked *