The actual implementation of the various services designed to meet road user expectations cannot be organised in the same way for all road networks. The extent of disturbances, traffic mix and traffic levels vary considerably, and the functions determined for different parts of the networks are subject to priority ranking. Operations will differ depending on the type of network, the numbers of users concerned, the frequency of the disturbances and their impacts on traffic flows.
The most appropriate level of operation for a given network depends on various parameters such as:
Based on this analysis, three operating levels can be defined:
Urban areas require the development of integrated transport planning and the categorisation of roads depending on the relative importance of their functions pertaining to traffic and local life.
Two categories of road form the trunk network of the urban area. They are:
Characteristics: Trunk networks in urban areas are subject to commuter movements relating to trips between home and work, which give rise to traffic levels causing the road networks to operate at saturation. The slightest incident can result in road congestion, which may rapidly degenerate into gridlock of the route and even of a major part of the urban area. But this network is often interlinked and there may be capacity reserves on some other road sections at all times.
Another feature of these networks is the complexity of responsibilities: there are many participating route owners and operators. Continuous consultation is necessary between authorities in order to:
Operational objective: The aim is to constantly optimise network use and balance competing demands between different classes of road user. The functions to be implemented are the permanent activation of traffic management plans drawn up by all the partners concerned. The network supervision system and information processing must be permanent and automated. This is the network on which the density of equipment for collecting and disseminating information will be the greatest. (See Urban Traffic Management, Urban Traffic Control and Urban Operations)
These networks include the motorways and associated main road network (parallel roads and alternative routes) that provide high capacity inter-urban motorway corridors and regional networks.
Characteristics: Over these heavily-trafficked corridors, designed for national and international through traffic, flow breakdown is frequent especially at beginning and end of the working week and with the onset of busy holiday periods. Their impacts are great as they concern a large number of users and can have upstream repercussions over long distances. In addition, disturbances on the main arterial roads can quickly extend to the parallel roads.
Operational objective: During incidents, the aim is to maintain the best possible flow conditions through optimum use of the network. It is essential to coordinate action between the management services. The resulting traffic management plans must be studied and implemented jointly, with preventive measures that may be required far upstream of the disturbance. They will be activated during the disturbance.
The functions to be implemented are the same as those of level 1. However, the density of equipment will be lower and it will be positioned according to the operational objectives: automatic incident detection in hazardous areas or detection limited to the most sensitive days; user information by variable message signs upstream of points where an alternative route can be chosen. (See Highway Traffic Management and Highway Operations)
Characteristics: These networks consist of roads with moderate traffic levels. These roads are characterised by the fact that major disturbances are rare and their impacts are localised. The number of users involved is also limited.
Operational objective: The main aim is to ensure good road serviceability as well as safe driving conditions over the entire network. For the management of random disturbances, it will generally be unnecessary to organise traffic management plans in advance, or to immediately restore normal traffic capacity on the road, but it is advisable to disseminate the best possible information on the level of inconvenience and its foreseeable onset. (See Travel Information Systems)
The functions to be implemented consist of organising foreseeable road serviceability operations such as winter maintenance, roadwork planning, and the organisation of convoys, events to limit inconvenience to users and information to users before they set out or during their trip. (See Regional Networks)