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Behind-the-Wheel

Knowing where to stop at a traffic signal

Triggering traffic signals

How about an article about the detection loops in the pavement at many traffic lights? Most drivers don't know what they are for and quite often stop too far ahead or behind them.

Once upon a time traffic signals operated on timers and would change according to the clock and not for any other reason. This could not reliably take into account the traffic flow changes that occur at different times of day and under different conditions.

Advancements in technology improved this, first with the inductive loop and now with the video camera. Each system has its use.

The inductive loop is a coil of wire embedded in the pavement at the approach to a traffic signal. An electric current is passed through it creating a magnetic field. When a large object containing iron, such as a car or truck, is near the loop, the nature of the magnetic field changes and the signal controller can take notice of it. If the vehicle stays at the loop for a set period of time the controller will cycle the signal to give the waiting traffic priority.

Problems occur when the vehicle does not stop over the loop. Too far ahead or too far back and the controller decides nothing is there and does not cycle the signals.

Unless the driver realizes and re-positions the vehicle over the loop, they may wait a long time for a green signal. So, pay attention to the stop line when you can see it, and make your best estimation when ice and snow covers it up. That will position your properly if you cannot see the tar covered loops in the pavement surface.

Some loops may not recognize motorcycles and bicycles because they don't contain enough iron to disturb the magnetic field sufficiently. Cyclists can make the traffic lights cycle by pushing the pedestrian signal button if one is present. For the motorcyclist, there are devices that attach to their vehicles that are designed to trigger the loop and cycle the signal.

Traffic signals may be controlled by video cameras instead of inductive loops. The cameras are able to accurately detect the presence of motorcycles, cyclists and pedestrians and change the traffic lights appropriately.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.



More Behind the Wheel articles

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About the Author

Tim Schewe is a retired constable with many years of traffic law enforcement experience. He has been writing his column for most of the 20 years of his service in the RCMP.

The column was 'The Beat Goes On' in Fort St. John, 'Traffic Tips' in the South Okanagan and now 'Behind the Wheel' on Vancouver Island and here on Castanet.net.

Schewe retired from the force in January of 2006, but the column has become a habit, and continues.

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To learn more, visit DriveSmartBC



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The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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