How are traffic signals triggered?

• A. By electrically charged wires buried under the pavement; the metal disrupts the current, and a computer directs the signal.
• B. By randomly changing signals.
• C. By manual operator input only.
• D. By sun position.

Answer: (A)

Traffic signals rely on detectors built into the roadway to know when to change. The most common setup uses induction loops—electrically charged wires buried under the pavement. When a vehicle sits over the loop, the metal in the vehicle changes the current in the loop, and the controller detects this change. The signal controller then directs the lights to switch, responding to real traffic conditions. This automatic sensing is why signals aren’t changed randomly or by sun position, and while some signals can be influenced by manual inputs in special situations, the usual trigger is vehicle detection by these roadway sensors.