[C4 Rides] traffic signal adjusting tool successfully tested

[Mark Ortiz]

It is very common for traffic signal sensors to fail to detect bicycles, and
even motorcycles.  When no car is present to trigger the light, this results
in bicyclists and motorcyclists being compelled to treat red lights as stop
signs.  The problem is so widespread that North Carolina, at the urging of
motorcyclist lobbying groups, has passed a law allowing a motorcycle to
legally run a red light that won’t change after waiting three minutes, if
safe.  The law does not specifically apply to bicyclists, however.  This
creates confusion as to how bicyclists are allowed to handle a light that
won’t change.

 

Even making it legal to treat the red light that won’t change as a stop sign
is often not a solution.  When traffic volume or sight lines truly require
an intersection to be signalized, often either the cyclist can’t get a break
in traffic allowing the cyclist to go, or the cyclist can’t see if any cross
traffic is coming.  In such situations, the signal really has to work, or a
very unsafe condition is created.

 

The problem of non-detection exists primarily because personnel in charge of
adjusting the sensors have lacked a reliable way to arrive at a setting that
detects small vehicles, yet does not produce false detection from large
vehicles in adjacent lanes.

 

Another problem is a general lack of understanding about bicycle detection.
Some people incorrectly think that traffic sensors can't detect
non-ferromagnetic materials like aluminum (in fact aluminum is easily
detected) or don't understand where the bicycle should be positioned for
sensing (for a conventional quadrupole, it should be over the center wire).

 

There are design tradeoffs between detection of long, high vehicles and
short, small ones.  Modified quadrupole layouts have been developed that
allow more sensitivity to small vehicles, over a wider area than sensors
that are common in most locations today.  However, most existing quadrupole
detectors will in fact detect even the lightest bicycles when positioned
over the middle wire, without producing false detection, if the sensor
control circuitry is adjusted properly.  Unfortunately, DOT personnel have
not had a convenient way of arriving at such a setting.  They consequently
set the detectors to a far lower sensitivity than actually needed, simply to
make sure to avoid false detection.

 

It no longer has to be this way.

 

There is a simple tool that permits a single person to easily adjust a
traffic signal sensor to detect bicycles, yet in most cases not be overly
sensitive and give false detection.  It has existed for some years, but is
little known.  It was developed by an engineer in California, Dr. Bob
Shanteau.  I know of it from Dr. Steve Goodridge, an electrical engineer and
cyclist who has been working to promote the use of this device in North
Carolina.  He has made a number of the tools, and has succeeded in getting
them into use in Raleigh, Cary, Durham, and Charlotte.

 

 

On Wednesday, February 19, 2014, I put this device to the test with an
actual signal, working with two NCDOT employees: JP Couch, Division 9
Traffic Engineer, and Marty Headen, Traffic Signal Supervisor.  We found
that the device works as intended.  I am writing to urge its adoption by
other NCDOT divisions, and by corresponding agencies elsewhere.

 

The device is nothing but a discarded bicycle wheel rim, mounted on a piece
of ¾” (one-by) lumber, using any non-metallic fastening system.  The wood
holds the rim upright, at a distance above the road similar to a narrow
tire.  It thus simulates the presence of a bicycle at the intersection.  The
device is placed atop the center wire of a typical quadrupole sensor layout,
and the control box is adjusted to the least sensitivity that will permit
the tool to trigger the signal.  The device is much easier to carry around
than an entire bicycle (I actually brought it to the test on my bicycle),
and because it holds itself upright, adjustment is an easy task for one
person.

 

We tested the signal with the device, and with my bicycle.  We found that
the device simulated the bicycle very well.  The same setting that allowed
one to trigger the light also allowed the other to do so.

 

When the signal was adjusted to the least sensitivity that would detect the
bicycle or the tool, we observed no evidence of false triggering or other
anomalous behavior.

 

 

The tool therefore offers a reliable, simple, and dirt cheap way to
eliminate a very common safety problem.  Neither Dr. Shanteau nor Dr.
Goodridge nor I claim any intellectual property rights to it.  We want
people in charge of adjusting signal sensors to use it.

 

In California, it is actually law now that traffic signal sensors be
configured and adjusted to detect bicycles.  With this simple tool, there is
no reason that similar standards of detector performance cannot be achieved
nationwide.

 

For more information, please see:

 

http://ncactive.org/sites/default/files/Background%20Paper%20on%20Bicycle%20
Detection.pdf

 

http://ncactive.org/sites/default/files/NCATA%20Position%20Paper%20on%20Bicy
cle%20Detection.pdf 

 

 

Mark Ortiz 

 

 

 



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