Anatomy of a Bicycle Friendly Street: Loop Detectors

We’re back today with another installment of what surely is your favorite bicycle infrastructure series.  Last time out we covered Traffic Diverters – the Cadillac of BFS treatments.  This week we’ll look at a much smaller, but no less important, treatment in the:

Anatomy of a Bicycle Friendly Street

Loop Detectors

Placing your bicycle correctly makes for a much more enjoyable ride

(Ed Note: Most information on Bicycle Friendly Street treatments come from the Technical Design Handbook in the draft 2010 LA Bike Plan.  Though we are happy to present it in bite-sized pieces, we highly recommend you download it yourself and have a good read.  You can download the Technical Design Handbook here.  For a refresher on what a Bicycle Friendly Street is -sometimes called a Bike Boulevard- you can read our introductory post here.)

Listed as a “Type 3” treatment for a Bicycle Friendly Street, loop detector symbols sit dead center in the range of street treatments.  While we’ll go into the specifics of how loop detector symbols can be utilized in a Bicycle Friendly Street, we should first cover what loop detectors are and how they work.

Changing Lights with Loops

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).

Not All Loop Detectors Are the Same

There are a whole range of loop detectors out there, and some are easier to use than others when you’re riding a bike.  There can be “Circular Loops”, “Square Loops”, “Q Loops”, and “D Loops”.  With all loops involved, it is key to have your bike on the outside of the loop and not in the middle.  If your bike is perpendicular to the loops, the electromagnetic signal may not be disrupted enough to trigger the signal.  In this case, a picture is far more illustrative than a description:

From the California Association of Bicycling Organizations

The City of Los Angeles currently uses circular loop detectors, the one in the top left of the graphic.  The best place to put your bike at an intersection is directly over the right or left edge of the loop.  Because circular loops are the least effective at picking up bicycles, the LADOT Traffic Signal Design Guidelines also call for a diagonal stripe to be put through all loop detectors adjacent to the “limit line” (the edge of the intersection) in order to better detect bicycles.  Check out page 8 in the pdf linked above for a good example.

The City of Los Angeles also has loop detectors specifically built for bicycles.  These typically are installed on bike lanes and resemble a smaller version of the “Square Loop” shown above.

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, please report them to LADOT and we’ll come out and fix or adjust them.  The length of time between signal changes once a loop detector is activated can greatly vary by intersection, so please be extra certain the loop in question isn’t functioning before reporting it.  The proper place to report a non-functioning loop detector is with your LADOT District Office.  How do you know what district office jurisdiction you’re in?  They roughly correspond to the Council Districts.

Gary Rides Bikes has documented poor loop detectors in Santa Monica

Bike Signal Stencils and More

So how does this all apply to Bicycle Friendly Streets?  Well, the Technical Design Handbook calls for specialized stencils (page 44) to be painted over loop detectors on roadways receiving “Type 3” or higher treatments as Bicycle Friendly Streets.

The stencil shows you where to trip the loop detector

Combined with signal priority along the Bicycle Friendly Street, converting problematic 4-way stop intersections into signaled intersections, and installation of street-facing push buttons, stenciled loop detectors built for bicycles help turn a street into a Bicycle Friendly Street.