A primary aim of network monitoring is to predict or detect traffic incidents or disturbances as quickly as possible, in order to take the necessary steps to remedy the situation in due time. Its quality is characterised by a detection delay (interval between the time the incident occurs and the time the management service is warned of this incident) and the reliability of the information collected. Incident detection and response forms part of most network management systems, although automated incident detection systems are not relied upon as much as in the past, since many incidents are now promptly reported using cellular phones.

Automated incident detection is most commonly found in urban areas where traffic congestion during peak hour periods is experienced. However, initiatives such as e-Call (Europe) are developing integrated emergency response infrastructure, which will improve detection and response to incidents in all areas (rural and urban) by means of global positioning, in-vehicle sensors and satellite and cell phone technology. In-vehicle systems where on-board electronics improve the driver’s competence in congested travel conditions, at night or in bad weather, can also reduce the occurrence of incidents. (See Automatic Incident Detection)

Performance Criteria

In the case of automatic detection, the reliability of the monitoring system needs to be evaluated after installation, with respect to the detection function, the telecommunications function, the data processing function and the overall system function. Typical evaluation points include accuracy of measurement, timeliness of data transmission and processing, ability to provide required data, reliability of software algorithms, system resilience under required environmental conditions and maintenance costs.

In the case of non-automatic detection such as phone calls from users, the reliability and accuracy of the data also becomes an important issue. Another issue is the problem of operators receiving too many calls with redundant information. This often happens in the case of large accidents that many people can clearly observe.

The purpose of this approach is to discover breakdowns in the flow of traffic that may not have been detected by traditional road operation equipment or services (automatic data gathering, mobile patrols, and other sources such as probe vehicles). Members of the public are encouraged to report traffic accidents, congestion and other problems. The information may mainly be received by telephone: cellular phones used from the car or emergency phones located along the road.

Information from road users can be gathered directly by the traffic or operations centre or through a dedicated call centre. In both cases it is very important to handle the gathered information quickly and to confirm its value through the use of the other information sources (such as loops, cameras, mobile patrols). Information from drivers can also be a complementary input for the traffic centre database and is an important tool where monitoring equipment is limited.

User feedback concerning the efficiency of the roadway and traffic conditions is a useful input for determining the perception of the network monitoring operation. This can be achieved through:

• roadwork preparation meetings, especially with local residents
• meetings organised as part of the assessment of specific operations measures such as regulated access, regulated speed
• specific meetings on themes defined in conjunction with user groups such as automobile clubs, motorcycle associations, cyclists, road professionals
• direct surveys within a pre-defined panel or undertaken in the framework of more general surveys on the quality of the road network

The aim here is to detect or predict any abnormal situation (weather or other) that is likely to affect the level of service to users of the network, in particular its safety of use. The requirements cover forecasts and detection as such and the integration of measurements into the prediction models. (See Weather Monitoring)

Detection systems can enable information to be given to the network operator regarding the onset (or probability of onset) of difficult weather conditions (fog, black ice, snowfall, cyclones, dust-storms) or other unfavourable natural events (landslides, floods). The network operator's task is to respond by issuing appropriate advice on road use through all available channels. (See Traveller Services)

Road works and bridge maintenance ( including rehabilitation and upgrading) can create substantial traffic congestion if not well-planned and properly designed. Alternative construction methods and working hours (off peak and night-time) will improve road serviceability and safety. Re-routing of traffic by means of pre-trip and en-route information about road works will help reduce congestion in these areas. (See  Planning Road Works) Planned special events may also cause significant traffic congestion if not planned properly, taking into consideration the extra travel demand created by the event and the impact of reductions in capacity on the road network (for example street closures). (See  Planned Events)

An important aspect of network monitoring is the gathering of information on traffic characteristics (such as flow, occupancy rate, speed, percentage of trucks and lorries) in greater or lesser detail in order to monitor or anticipate trends. The required qualities are reliability and completeness of the traffic data collection systems.

This requires systems for the collection, processing and centralisation of counts and information, organised relations with the safety and emergency call-out services or the assistance services, automatic or non-automatic warning systems (emergency call network, automatic incident detection), and the organisation of regular patrols on the most sensitive roads. (See Data Aggregation and Analysis)

Real-time data accumulation to serve as historical data is an important task of the monitoring mission. It can be used in such a way as to compare real-time data with historical data and find out the presence of incidents on the network. Before/after study of operations and control functions also depends on comparison of these data. In addition, historical data can provide important information to the ITS-unrelated programs of network improvement such as geometric improvement and pavement rehabilitation. (See Data Management and Archiving and Data Ownership and Sharing)