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Motorcycles and red light sensors, what to do?

Thomas Bachur's photo
Baltimore Motorcycle Travel Examiner

                                 A typical Inductive Loop Sensor                            (Photo: YouTube Video "Trigger Green Traffic Lights")

Part I – Red Light Sensor Problems

Larry, a reader from Pennsylvania recently emailed me a question:

I have been riding cycles now for twenty-three plus years.  With all the urban sprawl, there are more and more traffic lights.  A lot of the red light sensors don’t recognize motorcycles.  I find myself either waiting for a car to pull up and trip the light, making a right turn followed by a U-turn, or having to run the light.  Any suggestions?  I’ve seen light trippers advertised in some cycle magazines.  Do they really work?"

Larry describes a problem that most of us have encountered.  Several states (South Carolina, North Carolina, Wisconsin, Idaho, Arkansas, Tennessee and Minnesota) have adopted laws that allow motorcyclists to proceed through red lights with caution (usually after a specified period of time) when it is clear that the sensor will not trigger for the motorcycle.  Maryland and Pennsylvania have not adopted this law.

To answer Larry’s question, I decided to research this problem, investigate solutions and perform a product test of one of the many advertised “red light changer” products on the market.

My first step was to contact the people who know about triggering traffic lights: the Maryland State Sign and Light shop.  During this conversation, I learned that Maryland uses two types of intersection detection devices: video detection and inductive loop detection.

Video detection sensors are highly accurate and typically do not generate motorcyclist complaints. 

Inductive loop sensors are typically the sensors that motorcycles have problems tripping.  These sensors are imbedded in the road surface, near intersection stopping positions.  Inductive loop sensors utilize an electromagnetic field to detect metallic objects above the sensor.  In other words, the inductive loop sensors act like large metal detectors!  When these metal detectors sense a vehicle, they trigger the light to change.

Maryland’s inductive loop sensors are amplified, which means that they should detect any motorcycle 100 cc’s and larger.  However, issues can arise that cause an inductive loop sensor not to work as expected.  Problems include:

  • A broken sensor.
  • An improperly adjusted sensor.
  • Unaware riders who do not stop in the proper position to allow the sensor to “see” the motorcycle.

If the sensor is broken, it will probably not trigger for a car, truck or motorcycle.  In this case, the sensor problem tends to be reported and fixed rather quickly since it won't trigger for any vehicle.

If the sensor is improperly adjusted, it may trigger for a car or truck, but not a motorcycle.  This is the scenario Larry describes.  These improperly adjusted sensors often go unrepaired, as motorcyclists are so used to this problem, that they rarely complain.  As a result, the problem goes unnoticed by the repair crews who could adjust the sensor, had they known about the problem!

Riders must also know where to stop in order to trigger the sensor.  At many intersections, the location of the sensor wires can be seen as a square or rectangular pattern cut into the asphalt and then covered by tar.  It is best to stop alongside of one of the sensor loop wires, giving the mass of the motorcycle the best chance to trip the sensor.  If the road has been re-paved, the sensor location may not be visible.  In this case, it is best to stop a foot or so back from the white stop line, slightly off to one side of the lane.

The Maryland State Highway Administration "Signal Plan Locator" allows you to view the dimensions of state maintained intersections.  This includes information on the lay-out of any inductive loop sensors at the intersection.

The YouTube video below provides some good visuals of inductive loop sensors and then describes how the video author believes that using a magnet does help to trigger these sensors.

In "Part II - Red Light Changers" I'll test a retail magnetic "Red Light Changer" to see if, and how well it works.  I'll also test another "biker recommended" method for getting induction loop sensors to recognize motorcycles.

Click here to read Tom's other Investigative Reports.

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, Baltimore Motorcycle Travel Examiner

Tom's an avid rider, a Motorcycle Safety Instructor and an editor of the "Super Magna" discussion forum. Tom's been "riding Baltimore" for over 25 years. You can email Tom at tbachur@yahoo.com.

Comments

  • Ken 2 years ago

    I attached a super magnet to my CB750 years ago and it has never had any noticeable effect.

  • Woodbuchr 2 years ago

    Bills were introduced in both the Senate and House of Delegates last year at the request of ABATE of Maryland to address this very problem. The bill failed in the House Environmental Matters Committee because a Delegate of influence on the committee did not like the bill based on opposition by the Maryland State Police. The State Police's representative's main concern was not easing traffic congestion or passing a bill to allow motorcyclists to move out of a possibly dangerous situation but how they could write citations for an offense. Since they may not know for ceratin if a cyclist waited the full 3 minutes the law would have required they would have trouble proving guilt in court. This was enough for the bill to be killed.

    Please check the ABATE of Maryland web site during session next year for info

    The bill will be put in again next session. We would appreciate as much support and as many calls as possible be made to legislators asking for support of this bill.

  • Woodbuchr 2 years ago

    I did considerable research on this issue for testimony in last year's committee hearings and found some more interesting things. Did you know that if the sealant on the inductive loop has a break in it that rainwater can cause the inductive loop to fail but when the water dries it can start to work again?

    So if you report a light that failed while it was raining and the repairman checks it after it dries out he will find that it works and not neccessarily make any repairs.

    Many of the newer sport bikes do not have enough of the right kind of metal to trigger the signals. The bills mention earlier would also have covered bicycles. Many of which are made of carbon fiber.

    Also, the newer video detection sensors are not infallible either. They work on pixel changes sensed by the system and have to be adjusted within certain parameters and aimed at certain points in the intersection and can fail to recognize bikes if those parameters change.

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