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Do traffic sensors at intersections work for scooters, motorbikes?

By Steve Wallace, Special to the Times Colonist February 11, 2011

Some traffic lights are triggered by sensors under the pavement.

My last column contained a technological inaccuracy. The traffic light sensors that are embedded in the road before the crosswalk are in fact inductive loops.

These loops of wire, which are placed in the cut of the pavement, react to ferrous metal mass and sense when a vehicle is waiting at a red light. This electromagnetic resistance sends a message to the light control panel, which senses the change in inductive resistance and changes the red traffic light to green. These demand-type devices allow for prioritizing of the greatest traffic flow on some of our busiest highways and byways.

There are new wireless sensors that fit into a soup can-sized hole in the pavement.

No system is perfect, and this technology is no exception. It seems to work well for vehicles of significant weight. But what about motorcycles?

Several riders emailed me to express their frustration with the looping system, which they referred to as the “loopy” system. The ferrous metal mass on the lighter motorcycles and scooters does not trigger the sensors in the road.

One reader of this column, Rodney Wiebe of Nanoose Bay, might have inadvertently found the key to activating the sensor while riding his 400cc Yamaha. He says the bike is too light, with not enough metal mass to trip the mechanism that changes the traffic light in his direction. When he stops on the pad with his back wheel in the centre of the configuration, nothing happens. When he rides offset from the centre lane position, the sensor will often trigger and change the light to his advantage.

Gerry Brummund provided the best explanation for this phenomenon in a recent email to me. He maintains that most riders position their bikes in the middle of the cut section of the road, immediately in front of the crosswalk.

He recommends that riders put their wheels and weight on the cut in the pavement, thereby creating the largest magnetic field. (A big thank you to Don Barkley, Brock Johnson and Michael Blades for clarifying the looping rather than weight sensitive nature of the pads.)

The loops can be in several formations, as mentioned in the previous column, namely circular, diamond-shaped or rectangular. It was surprising how many drivers had never noticed them and thanked me for the (somewhat inaccurate) information.

By far the most interesting and entertaining story came from the above-mentioned Michael. He was first to stop at the intersection, on his motorcycle, in the left-turn lane governed by the flashing green advance arrow. Knowing full well that he would likely not have enough metal to trip the switch, he motioned the other drive behind him to advance onto the looping device imbedded in the roadway. The following driver had no idea what he had in mind, panicked and made a jerking lane change to the adjacent through lane and caused a near-mishap.

Luckily the driver behind the panicked person knew what Michael was up to and moved onto the inductive looping device, thus resulting in a streetlight “cycle” change (no pun intended).

On another topic, the use of the overdrive gear in an automatic, it was suggested by Roy Baldwin that overdrive not be used when towing a trailer. When I asked the head service representative at the Toyota dealership about this perceived problem, he replied as follows. The relative weight of the trailer to be towed and the power-to-weight ratio is really what matters in this situation.

There should be no problem with the more powerful V-6 or V-8 engines, but be very careful with four cylinder models.

Thanks to the readers for all the positive feedback.

Steve Wallace is a member of the College of Teachers and the owner of Joan Wallace Driving School on Vancouver Island and in the Interior of B.C.

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