Lefty
HOW TO – Fool a stoplight into thinking your bike is a car – The Loop Sensor Activator via Core77.

A common problem for bicyclists, and in particular for bicycle commuters, is the traffic loop sensor. These are the devices which detect the presence of vehicles to control the sequencing of traffic lights at many intersections. Often, they are installed in figure-eight slits cut into the pavement near a traffic light.

The way they work is to detect the slight change in inductance of the loop of wire buried in the slit caused by a large metallic object (such as a motor vehicle) above the loop. The problem for bicyclists is that traffic departments often feel compelled to set the sensitivity of the electronics behind the loop rather low, so that false detections are avoided. This can make it difficult for a bicycle (a relatively small metal object) to make its presence known to the sequencing circuit. The result is a lot of frustration for a bicyclist trying to get a green light or left-turn arrow. This can be especially frustrating at streets with low traffic (often where these sensors are used in the first place), as one waits for a motor vehicle to come by and trip the sensor. Sometimes one must resort to laying the bicycle down on the road surface above the loop with the hope that the extra metal presented to the loop will cause detection. Sometimes it doesn’t work, and sometimes frames aren’t made of metal.

Various devices have been patented in order to address this problem. Some are a little impractical, and some don’t work with modern loop sensor circuitry. One patented solution (see USP 5,652,577) has the bicyclist laying down a big piece of metallic foil or screen right on the road surface!

After studying this problem for many years, we have developed a new device (It’s patented! See USP 7,432,827) designed to be much more effective on a wide variety of loop sensors.

Phillip Torrone

Editor at large – Make magazine. Creative director – Adafruit Industries, contributing editor – Popular Science. Previously: Founded – Hack-a-Day, how-to editor – Engadget, Director of product development – Fallon Worldwide, Technology Director – Braincraft.


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