Originally Posted by cyccommute

Location. Location. Location. Cars are massive metal objects that trigger the loop no matter where they are located near the loop. Just being close to the loop is enough to trigger the signal. This is often a problem with the induction loops. Cars passing on the street perpendicular to the signal can sometime trigger them if they are set too sensitive. Motorcycles have to be closer to one of the legs of the loop to trip the signal. Bicycles have to be directly over the wires of the loop to trigger the signal. If I can see the cuts in the pavement, I will roll my bike directly over the center of the figure 8 or along the one of the legs of the loop if it is only a rectangular loop. I can trigger about almost all loop type traffic signals using this method.

Some caveats, however. First, I have to be able to see the loop. Paving often covers the loop and makes it next to impossible to find the wires. As the pavement ages, often it will crack and reveal the loop. Second, sometimes new loops are installed near the old ones and it can be difficult determining which loop is live. Since you have to be directly over the most sensitive part of the loop, I often choose the wrong wire. Rolling the wheel back and forth over the different wires can often tigger the signal. Third, sometimes the loop is deactivated and a motion sensor installed. the wires aren’t pulled up so this can lead to confusion. Look for the motion sensor camera on the top of the light post.

I will say that I find motion sensors harder to trip and have a lower success rate with them.