Green waves in use

The HALI project relates to the use of »green waves« for the police, fire service, and ambulances. Emergency vehicles often encounter full or blocked intersections and/or traffic lights on red, forcing them to stop at each intersection and proceed with caution. When responding to an emergency, however, every second counts – and collisions with emergency vehicles at intersections are among the main causes of accidents. The HALI project was launched with a view to preventing this risk and ensuring that emergency vehicles can pass through intersections unimpeded. As the idea originated in Finland, the acronym is derived from the Finnish phrase hälytysajoneuvojen liikennevaloetuudet (»traffic signal priorities for emergency vehicles«).

How does HALI work?

Thanks to the networking of traffic lights and reliable positioning of emergency vehicles, it’s possible to transmit positioning data to the lights as the vehicle approaches. Via a central HALI server, this data is combined with information relating to timing and the traffic situation so that traffic lights can be switched to green in an emergency vehicle’s direction of travel with pinpoint precision. At the same time, the lights are switched to red for other arms of the intersection. Galileo PRS ensures reliable positioning without the risk of improper use (spoofing) or interruption of signals by a noise source (jamming).