Make the Light Turn Green!

At the approaches to most intersections with traffic lights there are wires buried in the asphalt whose purpose is to detect approaching vehicles. They work by dectecting metal, not weight. Even the metal in the wheels of a carbon fiber bicycle is enough to trip a well-adjusted detector. Some detectors are adjusted so that they will only detect a bike in a certain position, or not at all.

Standard rectangular loops are most sensitive on the right or left edges. Often you can see the cuts made in the asphalt to bury the wires. For the best chance of activating the signal, ride directly over the cut. If that still doesn't work, leaning your bike over the detector in that area might help. If not your choices are to either wait for a car to trigger the signal or carefully go through on red. Going through on red is not illegal when the traffic signal is not operating, and if it doesn't detect your bicycle (a legal vehicle) arguably it is not operating.

Please also report the problem to the town where it is located or to the appropriate MHD district if on a state highway. Usually the sensitivity of the amplifier can be increased to a sufficient degree to detect a bicycle provided that the bicyclist knows to look for the loops and can see them. MassHighways has a policy, thanks to MassBike's request, to install quadrupole loops on all new projects. These loops can be sensitive anywhere, not just at the edges--if the amplifier is correctly adjusted. These new installations also typically have a sign, "Bicycle Stop on Line for Green." This means you are supposed to look for a bike logo on the pavement and wait there to trigger the green if no other vehicles are waiting. The new Federal standard for this sign text is, "Bicycle Wait on [Bike Logo] to Request Green," which is a lot less confusing.

This detection problem means that bicyclists must wait longer than others for traffic lights, which helps to explain why many ignore the lights. For more details and photos, see John Allen's article, Traffic Signal Actuators, Am I Paranoid?

Riding in Traffic
Traffic Basics
Obey Your Signals
Don't Get Doored
Road Hazards
Make It Turn Green
Stay Away from Trucks
Use Lights at Night