Motorcycles and red light sensors, what to do?

October 29, 9:56 AMBaltimore Motorcycle Travel ExaminerTom Bachur

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                                 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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