Green Wave

Definition and Working Principle

A green wave, also known as a green wave corridor, is an intelligent traffic light coordination and control technology. Its core principle lies in synchronising the timing offsets (phase differences) of traffic signals across consecutive junctions along a main arterial road, allowing vehicles travelling at a designated speed to catch successive green lights at every intersection, thereby ensuring a smooth driving experience with minimal or zero stops.

The name "green wave" originates from its visual effect: from behind the wheel, the green signals at upcoming junctions illuminate in sequence and propagate forward like a rolling wave.

Key Prerequisites and Limiting Factors

Green waves cannot be deployed everywhere, as they require specific road and traffic conditions. Essential prerequisites include: junction intervals typically under 800 metres with roughly equal or proportional spacing between junctions; closely matched traffic light cycle lengths across all intersections; minimal side-road interference and cross-traffic disruption along the stretch; and overall traffic flow remaining below saturation levels. Urban secondary roads and connecting corridors with junction spacing between 300 and 500 metres represent the ideal scenario for implementing green wave coordination.

Green Wave Speed and Traffic Flow Impact

Green wave speed refers to the recommended cruising speed motorists should maintain along an active green wave corridor. This speed is typically lower than the posted speed limit, yet considerably faster than the average crawl speed during peak-hour traffic. Green wave speeds often vary depending on the time of day and direction of travel—for instance, along Fudong Street in Taiyuan, the westbound-to-eastbound green wave speed is set at 30 km/h during morning rush hours, 40 km/h during off-peak hours, and drops to 35 km/h during the evening peak.

Green wave corridors deliver a tangible boost to traffic efficiency. Following green wave implementation on Liqin North Road in Guangzhou, average journey times fell from 166 seconds to 94 seconds—a 43.37% reduction—while average vehicle speeds increased by approximately 74.58%. After optimisation along Dayuan North Road, two-way stops were reduced from three to zero, slashing average travel times by 42.82%. Under ideal conditions, vehicles travelling along a green wave corridor can move over 50% faster than those stopping at red lights; under normal conditions, speeds improve by over 20%, boosting overall road capacity by around 15%.

Industry Application and Development Trends

Green wave technology has been widely rolled out across numerous cities. Shenzhen has implemented 574 green wave corridors covering 520 kilometres across 1,742 signalised junctions. Guangzhou recently introduced 41 new green wave sections spanning approximately 24 kilometres, expanding deployment from primary arterial roads to secondary urban roads and key link corridors.

Current green wave initiatives are evolving from isolated linear corridors into integrated, network-wide systems. Lanxi City plans to achieve comprehensive green wave coverage across major and minor arterial roads in its core urban district, supported by dynamic evaluation systems to fine-tune timings based on traffic flow fluctuations. Meanwhile, Hangzhou has adopted a modular approach—segmenting routes into shorter stretches of 3 to 5 junctions, accommodating curved corridors, and expanding from linear routes into area-wide grids. This has lifted average peak-hour speeds on green wave corridors in the city centre to 36.7 km/h, representing a 16.8% improvement over pre-implementation levels.

Technical Limitations

The effectiveness of a green wave relies heavily on driver discipline and manageable traffic volumes. Disruptions such as illegal parking, speeding, abrupt lane changes, and pedestrian jaywalking can compromise the green wave effect, causing drivers to fall out of the green window and get stuck at red lights. Under severe traffic gridlock and saturation, the benefits of a green wave are significantly curtailed. Furthermore, to prevent excessively long green phases that disrupt cross traffic, certain road sections still require designated stopping points, meaning a completely non-stop journey cannot always be achieved.