Cooperative Traffic TSoS Use Case. Despite the fact that the problem of real-time signal control at the junctions of urban traffic networks has been studied for many decades, and many different urban traffic control strategies have been developed, tested and are operational in a number of cities around the world, it is today a well-accepted fact that urban traffic control systems are not able to cope effectively with the constantly increasing problem of congestion. According to the American FHWA (Federal Highway Administration) “No current generally available tool is adequate for optimizing [signal] timing in congested conditions” (2008). Moreover, the problem of designing effective urban traffic control strategies will become significantly more complicated with the introduction of cooperative traffic/transport systems, whereby vehicles will be enabled to communicate directly with each other and with the infrastructure. Thus, apart from controlling the traffic signals in the junctions, the control system is also called to optimize the routes and speeds of the cooperative vehicles. In general, the existing real-time traffic control strategies can be categorized into centralized strategies, where the junction signals are controlled based on information from the whole traffic network; and local strategies where only the local traffic information is used for controlling the traffic signals at the - respective - local junction. Due to the high complexity of the problem, it is not possible for the centralized strategies to control each and every traffic light on a second-by-second basis (NP-complete problem); for this reason, centralized strategies provide their control decisions on a cycle basis, which practically means that they change their control decisions every 60-150 seconds [PDDKW]. On the other hand, local strategies are able to control the green times on a second-by-second basis but they are unable to incorporate and take into account information from other parts of the network. It has to be emphasized that the second-by-second control of traffic signals leads to significant delay reduction [Sh04, XSLB] at a junction level. In addition, it would be necessary to allow for the efficient cooperation between the junctions and the cooperative vehicles in the near future. An urban traffic network may seem, at first view, to have a steady and constant structure with respect to its subsystems (i.e. the junctions). However, the functional interdependencies between these subsystems are, in realit...
