Detection of traffic congestion is primarily accomplished through the use of inductance loop detectors, or vehicle detectors, embedded in the freeway pavement. Vehicle detector stations are located at approximately 600 metres intervals which transmit traffic data back to the Traffic Operations Centre every 20 seconds. A central computer at the traffic operations centre constantly analyses the data using an incident detection algorithm. The central computer system will alert the operator of a suspected incident and request a confirmation.
Closed circuit television cameras provide the primary means of confirmation. These cameras are placed about one kilometre apart with full pan, tilt, and zoom capabilities, effectively providing 100% coverage of the roadway. Once the incident is confirmed visually, the operator will proceed with a specific response plan and notify the appropriate response services.
The goal of the incident detection and confirmation strategy is to dispatch an appropriate response in a timely manner. As a result, the incident can be promptly dealt with and removed from the freeway.
Once an incident is detected and confirmed, the response and clearance must be managed so as to preserve and protect human life, maintain a reasonable level of safety for all participants, fulfil legislative requirements, minimize delay to the travelling public and minimize damage to public/private property. In a major incident, these are complex and often competing factors. Successful incident management can be facilitated by hi-tech equipment but is largely dependent on inter-agency co-ordination, education and on-site personnel.
The Traffic Operations Centre is the focal point for the MTO's freeway management activities within the area it controls. Not only is all the information from the Compass System transmitted to this point, but this is the same centre that receives all road condition, construction and maintenance activity reports. Due to the abundance of information available, the operations centre can often play a major co-ordinating role in incident management situations.
Private towing vehicles have free access to the highway and generally provide prompt but not necessarily an inexpensive service. The Ontario Provincial Police have jurisdiction over provincial freeways and are actively involved in incident management. Some cruisers are equipped with push-bumpers and lighted arrow-boards to clear and protect accident sites. Police personnel are key players in a large portion of the incidents and their response time is critical. Early detection of problems through the Compass system allows for easier and more efficient co-ordination of response activities.
In order to minimize the traffic impact of an incident, motorists must be supplied with timely, accurate and useful information. This may allow them to divert around the problem area, or at least will lessen their chances of colliding into the end of queue of stopped vehicles on the freeway.
Compass Systems use changeable message signs (CMS) located prior to strategic diversion points where motorists can choose between alternate routes. Within seconds of the confirmation of an incident, the central computer recommends a specific set of signs and messages based on the location and nature of the incident. The operator must review and approve the response plan before the messages are dispatched to the signs.
In addition, the Traffic Operations Centre staff in Toronto Compass Systems operate a Traffic and Road Information System (TRIS) covering all provincial highways within the Greater Toronto Area and the Niagara Peninsula. Traffic reports are automatically faxed to the media and emergency services on both a requested and an emergency basis. The traffic reporting media can be an extremely effective tool for communicating with motorists.
An effective motorist advisory strategy not only encourages diversion and driver vigilance, it also reassures the travelling public that the responsible agencies are aware of the problem and doing their best to manage the situation.
Regardless of whether congestion is being caused by an accident or normal rush hour traffic, the changeable message signs are capable of automatically displaying information related to the level of congestion on the freeway. In the Toronto Compass System, the messages describe the average traffic conditions on the express and collector lanes for a pre-defined upcoming section of the freeway. The average traffic condition is defined in terms of "MOVING WELL" (75 km/h and above), "MOVING SLOWLY" (40 to 75 km/h), and "VERY SLOW" (less than 40 km/h). Motorists may use this information to decide whether to continue travelling on their original route or take an alternate route by transferring onto the express or collector lanes. In the Missisauga and Burlington Compass Systems on the Queen Elizabeth Way, the congestion messages describe the average traffic conditions and the congestion area boundaries with respect to the CMS location. If the CMS is upstream of the congestion area, the message will warn motorists where the arrival end of the queue starts. If the CMS is already within the congestion area, the message will let motorists know the downstream end of the congested queue.
The congestion management program is a fully automated system using data from the vehicle detector stations installed in the Compass System to select and display congestion management messages on the changeable message signs. As often as every 20 seconds, the Compass computer calculates the travel time for vehicles over pre-defined sections of the freeway and updates the messages on the signs based on the average speeds and travel times calculated. Used properly, this traffic information can help balance the traffic flow, maximize roadway capacity usage, reduce motorist travel times, and improve safety on the freeway.