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Sensors should be picking up motorcycles
Published November 10, 2009
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Glad You Asked features questions from Facts readers. Facts staff members pose those questions to newsmakers who provide the answers.
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QUESTION: I have a question for local law enforcement and the Department of Transportation that I am positive many others have: Why won’t the light change to green?
I own and frequently ride a motorcycle. When I come to an intersection, the light will not change. I have tried everything to make the light change (backing up, going to one side, pulling forward, etc.). When I was in college physics, we studied electro-magnetism and I realize this is why it will not change for motorcycles. Motorcycles are mostly aluminum and it does not produce an electric current when traveling over the coils in the intersection. The Department of Transportation has to know this already, but why haven’t changes been made?
My final question is what motorcyclists should do when stuck at a red light for three or four cycles, wait for God to change the light or risk getting in an accident or receiving a ticket?
ANSWER: The Texas Department of Transportation uses several different vehicle detection systems at our actuated traffic signals.
The first type is the video imaging vehicle detection system, or VIVDS. In this type of detection, a computer looks at a video image to detect vehicles. You can tell if it is this type of detection by looking for cameras at the signal. By the way, these are different from the red-light cameras some jurisdictions are installing and no video recording is made from these cameras.
The second type is the inductive loop detector. In this type of detection, a loop of wire in the pavement has an alternating electrical current running through it a certain frequency. When a vehicle passes over or stops on the loop, it causes a decrease in the loop’s inductance, which increases the frequency of the electrical current. If the roadway has not been overlaid with fresh asphalt, you usually can identify this type of detection by looking for saw cuts’ outline (typically square or rectangular) in the pavement.
Both types of detection systems are capable of detecting motorcycles, so the fact they are not being detected means the detection system needs maintenance. This could be as simple as cleaning the cameras lens or adjusting the sensitivity of the loop detector. If you are having problem with your motorcycle being detected at a TxDOT signal, please report it so we can make some adjustments to the detectors.
We often get asked where is the best place to be on the loop detector to make detection more likely. A loop detector is most sensitive directly above the wire, so a motorcycle is most likely to be detected when it is stopped directly over and aligned with the saw cut seen in the pavement. This is usually about 3 feet on either side of the center of the traffic lane.
Note that the state highway department maintains traffic signals only on state routes that are not within the limits of a city with a population greater than 50,000. You can tell if the signal is a state highway department signal by looking for the TxDOT logo and dispatch number on the signal controller cabinet. To report a concern about a TxDOT signal, call 713-802-5662.
J. Dan Maupin,
Signal Timing and Operations Supervisor
Texas Dept. of Transportation-Houston District
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