Flashback Friday: San Diego bicycle detection report, 1985

Longtime California cyclist advocate Bob Shanteau sent this 1985 report on traffic signal bicycle detection and asked me to archive it here at Cyclelicious.

San Diego bicycle detection report 1985

Everybody who cycles on American roads has likely encountered problems triggering a green light at intersections. This report looks at solutions used in other cities, including the now-familiar bicycle pavement stencil that was apparently pioneered in Boulder, Colorado and San Luis Obispo, CA. This stencil helps cyclists identify the placement of their tires over the detection loop embedded in the roadway.

Green bike lane Hedding Street

The report discusses the problem (cyclists can’t get across many San Diego intersections) and proposes solutions, including technical discussion on inductive loop placement, sensitivity settings, and training for the signal technicians who maintain traffic lights. The report’s discussion on “beg buttons” notes their shortcomings for cyclists, recommending their use as supplements rather than replacements for in-pavement detection methods that require no interaction by the cyclist.

Some fun quotables from this document highlight both how far we’ve come with cycling and cyclist advocacy in California, and how far we have to go.

  • “Changes in the traffic signal systems to enhance their usefulness by bicycles should not be made at the expense of the majority of road users.”
  • “The cost of pedestrian push buttons is very low and no additional controller equipment is required. Theoretically speaking, if a pedestrian can be trained to push the button, then a bicyclist, with apparently more skill by virtue of the fact that he/she hasn’t fallen down, can also. The obvious flaw to this theory is that too many pedestrians don’t bother to push the button before crossing the street and bicyclists’ behavior can probably be expected to be similar.”
  • “Local bicyclists suggested … add some device” [e.g. a transponder of some kind] “to the bicycle to make it easier to detect at traffic signals.” [For whatever it’s worth, I continue to hear similar suggestions today.]
  • Regarding early experiments with pavement stencils to aid in positioning on detector loops: “A review of time lapse films, taken before and after, shows no evidence that the bicyclists understood the purpose of the markings.”

Today, all new actuated traffic signal installations in California are required to detect bicycles thanks to AB 1581. California law also mandates green light timing that gives cyclists enough time to cross intersections for new traffic signal installations.

You can download and read the full 48 page report as a scanned PDF here.


  1. Yet there are many, many lights that detect bikes, yet cycle through too quickly for any bicyclist who doesn’t accelerate like a racer. This includes lights on marked bicycling routes. Do we have any recourse to get those changed?

  2. So back in 1985 people didn’t know, cyclists included, what the little bike stencil was for. Fast forward to today where I’m still educating cyclists about the symbol on the road…. Many ‘standard’ bike signs need to go into the driver’s written test so it will, in theory, increase the knowledge base.

    Evidently only 1 bike question is allowed.

  3. Teacher lady. Currently your best recourse in to contact the city’s traffic maintenance dept and copy the city Bike/Ped advisory commission to push on this for you. Sunnyvale’s is reasonably responsive, how ever they like to count the whole time the green and yellow are on to clear the intersection. I know where you are coming from on this as I have one intersection which is red before I clear on a left turn.

  4. Are position stencils supposed to be required for all intersections with bike detection?

    Anybody know how the Hedding street bike detection study is coming along? I heard they are trying different systems to find out which is the best one to standardize on.

  5. Although AB 1581 requires bike detection, I believe that the statement in the blogpost about timing (” … California law also mandates green light timing that gives cyclists enough time to cross intersections for new traffic signal installations”) isn’t true. Caltrans did create a Policy Directive (TR-0011**) that provides a table that local traffic engineers can use to adequately time the signal to safely accommodate bicyclists, it is supplied as “guidance”, and not a “standard”. Therefore, there is no force of law compelling the use of these longer initial and gap times in the signal controller. In 2006, when California took this first-in-the-nation step toward accommodating bicyclists, there were no detection systems on the market that could discriminate between cars and bicycles in the same spot. So, it was prudent to make the timing aspect a recommendation rather than a requirement. Multiple vendors now make and sell detection devices that can differentiate between cars and bikes in the same location. Cyclists everywhere (not just in CA) should be pressuring their local traffic engineers to get with it.

    (** read it for yourself: http://www.dot.ca.gov/hq/construc/CPDirectives/Attachment5_Traffic_Ops_Policy_Directive_09-06.pdf)

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