Modeling and Optimization of Traffic Flow in Urban Areas - Czech ...

1.1 Related Work 3Traffic stream models [Cast 96], [Masu 07] consider traffic flow as a heterogeneoussystem which can be described from a macroscopic or microscopicpoint of view [Tolb 05]. The macroscopic point of view is described by globalvariables as the flow rate, the flow density and the flow average velocity[Gazi 02]. On the other hand, microscopic point of view focuses on the individualvehicles behavior on the road [Nage 03].The light controlled intersections are characterized by several parameters:the number of light phases, phase split and offset time [Gube 08]. The termphase means the state of traffic lights on the intersection. Phase split definesthe time interval of phase for which the vehicle flow can go through the intersection.The offset is a certain time delay between phases of two successiveintersections [Papa 03].The control of a single intersection (belonging to the class of road trafficcontrol) is usually based on a fixed-time strategy or on a traffic-responsestrategy. In a fixed-time strategy (see, e.g., the TRANSYT tool [Robe 69]),the light control phases are scheduled offline. This approach is optimal onlyin the case of the under-saturated intersections. The light control phases arederived from the historical data measured for a given intersection. Thereare typically several light control phases for each intersection, dependingon the given time of the day [Febb 06]. The traffic-response strategies arebased on feedback from the current state of the traffic (e.g. the SCOTT tool[Hunt 82]).The optimization of the traffic flow over several light controlled intersectionsin urban traffic region can be improved by the synchronization of lights.The three main synchronization strategies are: synchronized, green wave andrandom strategy [He 06, Naga 07]. In the synchronized traffic light strategy,all traffic lights switch from red (green) to green (red) simultaneously. In thegreen wave traffic light strategy, the lights switch with a certain time delaybetween two successive lights. In the random switching traffic lights strategy,all traffic lights change independently in an allowed range.