Online Microscopic Traffic Simulation Supports Real-time Traffic-management Strategies

Quantitative decision-making relies on appropriate mathematical models of the systems about which decisions are to be made. Intelligent transport systems (ITS), which apply combined advanced detection, communication, and computer science technologies to traffic and transport systems, are im-portant examples of such quantitative decision support systems. Figure 1, adapted from [10], depicts the logic diagram for an advanced traffic management system (ATMS), a paradigmatic case of ITS. This generic ATMS assumes that the network is equipped with an appropriate layout of detectors that provide real-time measurements of traffic variables, flows, speeds, and occupancy levels; these measurements constitute the main input to traffic models that are solved to estimate the current state of the network and forecast its short-term evolution. System performance is estimated in terms of “measures of efficiency” (MOE): travel times, delays, mean queue lengths, and possibly others, depending on the manager’s objectives; the latter can include estimates of fuel consumption and emission levels when the sustainability of the transportation system is to be taken into account. The estimated system performance and its predicted short-term evolution are then compared with the management performance objectives (e.g., minimize congestion, travel time, or delays, or hold emissions under critical threshold values); in the case of significant deviations, appropriate management strategies are activated (linear speed control, ramp metering, rerouting policies, changes in signal timings, and so on) and put into operation by appropriate ITS devices (variable message signal (VMS) panels, adaptive controllers, in-car information systems, and so on). Of particular interest for reallife applications is the case in which the ATMS is called on to support real-time management in response to incidents or situations, recurrent or not. In such cases, the system needs additional functions, such as: