Fixed-time, actuated and adaptive control
Fixed-time control runs pre-calculated signal plans, often different by time of day. It is simple and predictable, but it cannot react to changes in demand.
Vehicle-actuated control uses detectors to extend or skip green phases at a single junction, within limits set by the designer. Adaptive control goes a step further: it measures demand over a junction or a whole network and optimises cycle time, green splits and offsets between junctions as conditions change.
How adaptive control works
- Detection measures the traffic: inductive loops, radar, video or thermal cameras, and push buttons for pedestrians and cyclists.
- An optimisation algorithm in the controller or in a central system estimates queues and arrivals and adapts the signal timings, either cycle by cycle or second by second.
- Coordination links neighbouring junctions, so that platoons of vehicles meet green signals along a corridor.
- Safety rules always come first: minimum greens, intergreen times and conflict monitoring are guaranteed by the controller, whatever the optimisation decides.
Well-known adaptive strategies include SCOOT and SCATS, and many controller manufacturers offer their own adaptive or self-optimising functions.
Priority for public transport, emergency services and cyclists
Priority requests can come from vehicle location systems, short-range radio or C-ITS messages. The controller then extends or brings forward a green phase for an approaching bus or tram, or clears the route for an emergency vehicle. Cyclists can be given earlier or longer greens, for example based on dedicated detection.
Intelligent controllers such as the Dutch iVRI also publish their signal timings (C-ITS SPaT/MAP messages), so that vehicles and apps can anticipate the next change.
Standards and integration
Traffic signal controllers are designed and tested according to European standards such as EN 12675 (functional safety of traffic signal controllers) and EN 50556 (road traffic signal systems). Communication with central systems uses open protocols such as OCIT, NTCIP or UTMC. With open interfaces, existing controllers can often be connected to a new central or adaptive system step by step instead of being replaced all at once.
When does adaptive control make sense?
- Corridors and networks where demand varies strongly during the day or between days.
- Junctions with public transport lines that need reliable priority.
- Cities that want to manage traffic actively from a control centre, for example during events or roadworks.
- Locations where fixed plans are outdated and expensive to keep up to date manually.
A study or traffic model beforehand shows whether adaptive control, better fixed plans or a mix is the right choice for a specific network.
Maintenance and performance monitoring
A traffic signal installation only performs as designed when its detection works. Faulty loops or misaligned cameras silently push a controller back to fallback timings. Remote monitoring of controller alarms and detector status, preventive maintenance and periodic reviews of the signal timings keep the installation effective after commissioning.
Logged controller data — green times, waiting times, priority requests served — also makes it possible to check whether the objectives of the project are being met and where fine-tuning is needed.
How Urbiflow helps
We design signal timings and detection, select and configure controllers from leading manufacturers, integrate them with central and adaptive systems, and test and commission the installation. Afterwards we maintain it with agreed service levels. See our product examples for an urban intersection controller, adaptive corridor control and pedestrian and cycle crossings.
Relevant for: Cities & municipalitiesRoad & highway authoritiesContractors & EPCs