TOTW: Make those automatic traffic lights change

The riding tips on these pages are my personal opinion about matters related to motorcycle riding. They are not the official position of any organization, and are for your consideration only. They are not hard and fast rules, they should not necessarily be applied in all circumstances, and they should not be applied without thinking. Always use your judgement and take all current safety factors into account while riding. You are responsible for your riding, not anyone else (especially me). These tips were originally published by a motorcycle riding course, called “Tip of the Week” (the reason for the TOTW in the titles).

What’s the problem?

Many traffic lights at intersections use vehicle sensors to control when the lights change. For example, if there is no car waiting to turn from the left-turn lane, a sensor-controlled light will bypass the left-turn cycle, allowing more through-traffic to proceed.

The sensors, however, can have trouble sensing motorcycles. When this happens, you might find yourself sitting at a red light through entire cycles, with the signal you need to proceed never appearing.


Sensor-controlled signals are activated when an induction loop buried in the asphalt senses a vehicle’s magnetic field. (The mass of iron in the vehicle disturbs a small current in the loop of wire in the pavement, and this is detected by circuitry.) Small vehicles such as bicycles and motorcycles may not contain enough iron to trigger the sensor. Even a large motorcycle that should have enough iron is smaller than a car might be stopped away from the sensor wires, and go unnoticed by the sensor.

Note the sensors detect ferrous metal disturbing the current in a wire; they are not weight sensors. (Some riders who think the intersection is triggered by vehicle weight assume the rectangle in the pavement is a “weigh scale” and that you should position yourself in the centre of it. This is the wrong move, as it moves you further from the sensor wires.)

The solution is to be sure you stop your bike over the sensor wires. You can tell where they are by looking for a hairline slit in the pavement, near the stop line, outlining a rectangle about the size of a car.

If stopping over the wire doesn’t work, look for three yellow dots, each about 8 cm3 inches
in diameter, positioned somewhere along the loop — usually on the right. These mark an extra-sensitive portion of the loop, and are designed to detect bicycles. If you position your motorcycle over those dots the sensor will almost certainly detect you.

There are also unconfirmed reports from some riders that varying your throttle speed (revving your engine) while over the wires will make the sensor notice you. This is theoretically possible, since revving your engine will vary its magnetic field; but we’re unaware of any studies confirming it.

There are also unconfirmed reports that putting your side stand down on the loop will trigger it. Again, this seems plausible, but we don’t recommend it because of the risk of forgetting to put it up again.

If you find that the lights at an intersection still won’t change, even when you are positioned correctly, you will need to wait until another car joins you to trigger the sensor, or until you can safely change lanes and proceed in a direction that is working. You should then report the intersection to the city’s Traffic Management Section and they will investigate and make adjustments to the induction loop in the pavement.

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