Traffic Flow Theory

The frequent occurrence of perturbations in traffic flow, such as sudden deceleration of vehicles, or the non-uniformity of the flow entering a highway from an on-ramp, may, under circumstances, lead to stop-and-go waves traveling upstream, or traffic jams, resulting in considerable time-delays, increased fuel consumption and air pollution, as well as a serious under-utilization of the available infrastructure. Consequently, traffic flow stability analysis is considered to be one of the fundamental tools in traffic flow theory, and scientists have been particularly interested in understanding the formation and evolution of such traffic flow instabilities since the early days of traffic engineering. In general, there are two main modeling approaches

More specifically, using a forward-looking range sensor, the ACC systems are able to estimate the time gap to the vehicle immediately in front of them -referred to as the leader-, the speed difference, as well as the speed of the equipped vehicle. Hence, in cases that the leader drives at lower speed, the ACC-equipped vehicle slows down to realize a desired time-gap, while, on the other hand, in cases that the leader either accelerates or is out of the range of the ACC vehicle’s sensors, the equipped vehicle accelerates towards and maintains a pre-set desired speed. ACC systems have been focused on increasing driving comfort and safety, by relieving the driver from continuous speed and time-gap adjustments; however, for particular selection of their operation parameters, they may have negative consequences on the traffic flow performance and stability. Hence, research is focused on the development of effective (theoretical and numerical simulation) models for traffic flow including ACC-equipped vehicles, to provide tools for the evaluation of their effects on the traffic flow stability and efficiency. However, a significant query regarding the applicability of such tools is whether they are capable of reproducing the mechanisms leading to stop-and-go waves

Οn the other hand, the corresponding literature pertaining to macroscopic or gas-kinetic traffic flow models is relatively limited [19-23]. It is worth mentioning here that the stability analysis using macroscopic models is referred as flow stability, while the string stability of a platoon of vehicles is obtained from microscopic approaches [20, 24]. However, concerning the models applicability, macroscopic traffic flow models call for much less computational demand than their microscopic counterparts and require simpler calibration and validation effort; hence, the development of such models for the simulation of ACC traffic will be of major significance in the