Adaptive traffic signals

Adaptive traffic signals change their timing in real time to match the traffic that is actually there, instead of running a fixed schedule set months earlier. Sensors — cameras, road loops or radar — count vehicles at each intersection, and software constantly recalculates how long each light stays green, so a coordinated green wave forms and re-forms itself as demand shifts rather than being timed by hand.

The goal is to cut the stop-and-go that wastes fuel and patience. Designs range from one central computer coordinating a whole city, as in Wiesbaden's DIGI-V network of 227 signals, to decentralised systems where each intersection negotiates with its neighbours, like Pittsburgh's Surtrac. The US Federal Highway Administration estimates adaptive control improves travel times by more than 10% on average.

The honest caveat: adaptive signals are the most expensive way to coordinate lights, needing dense sensors, reliable communications and staff to run them. Hardware alone fixes nothing — Dhaka installed automated signals across 29 junctions that sat unused as police kept directing traffic by hand. Benefits also shrink where roads are simply saturated: no timing tweak conjures road space that isn't there.