How Traffic Lights Know You're Waiting

Many traffic lights detect cars with a buried coil of wire whose inductance drops when a vehicle stops over it. Here is the full circuit, and why it ignores bikes. A common way for traffic signals to detect vehicles is an inductive loop: two to four turns of insulated wire in a sawcut, wired as the inductive half of an oscillator running between about twenty and one hundred kilohertz. A vehicle's conductive underside carries eddy currents that oppose the loop's field, inductance falls, frequency rises, and a detector card declares a call. Motorcycles and carbon-framed bicycles couple poorly because they present little conductive area, and much of it stands upright rather than lying flat over the wires. The second half of the video follows that single bit of information into the controller: minimum green, passage timers, gap out and max out, then coordination along an arterial, where a fixed cycle length and force-off point can leave a legitimate call waiting a full cycle. It ends with how loops fail, why a broken one puts a phase on constant recall, and what magnetometers, video and radar do differently. Chapters 0:00 Intro 0:20 The sawcut in the road 1:32 The oscillator in the cabinet 2:48 Eddy currents, not magnetism 4:07 Why the bike gets ignored 5:24 What a call does to the timer 6:42 The green wave outranks you 7:50 When the loop dies Sources and further reading: Federal Highway Administration, Traffic Detector Handbook, Third Edition NEMA TS 2, Traffic Controller Assemblies with NTCIP Requirements FHWA Traffic Signal Timing Manual Institute of Transportation Engineers, Traffic Engineering Handbook Music: "Deliberate Thought" by Kevin MacLeod (incompetech.com) Licensed under Creative Commons: By Attribution 4.0 https://creativecommons.org/licenses/... #TrafficLights #InductiveLoop #VehicleDetection #HowItWorks