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Stuck Signal Lights
Sensible Approaches

By: Cash Anthony



A group of experienced tour riders I know started a rider safety conversation recently about sensible ways to handle a ‘red light is stuck’ situation. While automobile drivers usually have little reason to notice signal light sensors and how they work, the information that was shared may be quite interesting to motorcyclists. I can’t say that this information is ‘gospel,’ but it sounded pretty accurate to me.

First, there are two types of signal lights: timed traffic signals (signals that follow a sequence based solely on time) and actuated signals (signals that alter their sequence based on demand). Actuated signals are activated by vehicle detectors.

Several types of vehicle detectors are in use today in the United States. These include 1) video cameras that detect movement; 2) radar units that detect movement; 3) sonar units that detect distance to an object; 4) magnetic sensors that detect changes in the earth’s magnetic field caused by moving metal; and 5) loop detectors. Video cameras, radar, sonar and laser detectors are being used for various kinds of traffic control; some are already installed on the Houston freeways and on toll roads. Especially at rural intersections with fitful traffic patterns, signal lights may be video controlled. In most cities and states, however, loop detectors are used.

A loop detector is the most popular device used to govern traffic signals, probably accounting for more than 90% of the detectors in use in the United States. These work just like a metal detector. Typically, three or four turns of wire are placed in or below the pavement in a 6'x6' loop. Multiple loops may be installed to extend the detector’s coverage area.

Some riders who are faced with a ‘stuck’ red light may think that a Gold Wing or other motorcycle isn’t ‘heavy enough’ to trip the sensor. Clearly this does not happen at all intersections, but most riders know of one or two where the lights regularly fail to change when they pull up on their bike, but change for a car. Does weight make a difference?

Because the sensor is a metal detector, a vehicle’s weight doesn't really affect it. It reacts to only the presence of metal (or an electromagnetic field). Most of these loop sensors merely serve as an antenna known as a whetstone bridge. When a certain mass of iron interferes with the balance of the circuit, the circuit reacts. If the electrical value of the antenna/bridge changes in any way, the voltage will be changed, triggering a relay to switch the lights. These sensors detect large masses of metal, and a touring bike surely qualifies. A sensor may be out of adjustment, however.

The sensitivity of a loop detector varies due to a number of parameters. It is affected by its front panel sensitivity setting, the number of turns of wire in the loop, the number of loops that are connected to one detector unit (the electronics of the device is called a detector amplifier), and the length of wire connecting the loop(s) to its detector unit. Additionally, a loop can be incorrectly installed right next to concrete rebar, which tends to overwhelm any signal coming from vehicles above. It is also possible to put a loop too far below the surface of the pavement.

While you are sitting there "stuck at the light," one additional thing to remember is that the traffic signal may forget you’re there. In the case of motion detectors, the device’s memory must be turned on. (Also note that it does no good to roll up slowly to an intersection that employs a motion detector). But with loop detectors, because they detect presence, memory is often turned off. Turning it off prevents the signal from constantly changing for vehicles that have made a right-turn-on-red. However, if your bike goes beyond the detection zone, the device will forget you, and you’ll sit and sit.

There are some tips that may help you outwit these witless devices. First, start noticing where they are. Traffic intersections are often grooved so that detector loops can be buried. Grooves may run both perpendicular to and parallel with the direction of travel. If the paving contractor installs the wire loops after paving the road, you may see the saw cracks from loop installation. If you can't see the loop, you can usually presume it is a 6’x6’ loop, centered in the lane and probably six to twelve feet behind the stopbar.

Thus, if a motorcyclist can’t depend on a car to trigger a signal light to change, then the best place to stop for a signal light is probably three feet to the side of the center of the lane, with the front tire about six feet behind the stopbar.

Before you decide to run a red light that’s ‘stuck,’ here are a couple of other ideas you might want to consider (besides checking in your mirror):

  • Pass your motorcycle directly over the lines marking the perimeter of the sensor. You may even roll back a couple of feet to help the sensor "see" the bike. Depending on where other traffic is stopped or moving nearby, this may or may not be possible.


  • After sitting through one cycle of the lights, some people put their side stand (or center stand) down -- the idea being that having actual metal touch the road helps.


  • You might position your bike right on top of the "line" cut into the pavement, then hit the kill switch and restart your engine. On a marginally maladjusted sensor, this may create enough of a magnetic field to trip the light. (Another suggestion is to hit your starter button without turning your engine off, as it will have a similar effect.)


  • If you know you must cross a dangerous intersection where this problem often exists and you have not been able to get it fixed by your local officials, consider changing your route or going around an extra block to avoid the intersection.


  • If there is a "pedestrian button", consider getting off the bike and pressing that button.

If nothing else works, especially for a group of riders committed to a particular course of travel, wait until traffic clears, then run the red light carefully. You may want to wait through more than one full cycle before taking this course of action, to be sure you are not perceived by other drivers as simply flaunting the law.

If you know of traffic lights in your area which routinely fail to change in response to the presence of a bike, the sensitivity of the detector is out of adjustment. Out-of-adjustment sensors should be reported to your state highway department or to the agency responsible for maintaining local traffic controls.

Copyright © 1992 - 2019 by The Master Strategy Group, all rights reserved.
http://www.msgroup.org

(James R. Davis is a recognized expert witness in the fields of Motorcycle Safety/Dynamics.)

     
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