Real-Time Stochastic Optimum Control of Traffic Signals

In accordance with the increase of vehicles recently, traffic congestion has become a serious problem. In urban areas, almost all traffic congestion occurs at intersections. Intersections can be classified into three types according to the number of roads meeting at the intersection: T-junction (3-way intersection), Crossroads (4-way intersection), and Multi-way intersection (more than 4 ways). The traffic signal phases are generally more complicated at multi-way intersections and consequently traffic jams occur more easily. One of the ways to solve this problem is road expansion, but high costs and long construction periods make this option difficult in urban areas. In such cases, traffic signal control is a reasonable alternative method for reducing traffic jams. Traffic signal controls can be classified into two types. One is an offline (pretimed) control and the other is an online (adaptive) control. In the pretimed control, Webster’s formula is used to calculate the traffic signals offline using historical traffic data, but it cannot handle variation in traffic flows. On the other hand, an adaptive control can overcome this limitation by adjusting the traffic signals online in the various traffic flows. SCOOT [1], SCATS [2], and OPAC [3] have been implemented on urban traffic networks using centralized systems. However, these centralized systems require extensive data processing and computational time for calculating adequate traffic signals. In an approach using