Pre-emption of traffic signals by emergency vehicles has been a requirement at signal locations for a long time, but it has hitherto needed local devices that have been expensive and have other disadvantages. Traffic networks for city centres typically have a central computer system, which is responsible for co-ordinating all traffic systems there. The RESPONSE (Real-time Emergency Signal Pre-emption Operating in a Network Signal Environment) system in Ottawa, Canada has been created as a new approach to a traffic signal pre-emption system, using a central computer, which overcomes these disadvantages. To implement the system, it was necessary to locate both emergency vehicles and traffic signals very accurately at all times. In the system that was developed, the only equipment that had to be installed was a satellite Global Positioning System (GPS) and a cellular modem on each emergency vehicle. No equipment was needed at a junction except its currently installed traffic controller. Tests of the system during the proof-of-concept stage showed that relevant data were transmitted accurately enough and sufficiently rapidly to implement the pre-emption strategy. The key to developing the pre-emption logic was to identify and resolve the complex algorithms to determine position and handle junction geometries.
Abstract