Urban Congestion Reduction for Energy Conservation: Control Strategies for Urban Street Systems: A State of the Art: Final Report

The primary objective of this study is to acquire an understanding of the current state-of-the-art of traffic signal control strategies at urban street systems. Signalized intersections can be classified into three types: (1) an isolated intersection; (2) an arterial street; and (3) a network. For the analysis of isolated intersection capacity and performance, the commonly used methods include the U.S. Highway Capacity Manual (HCM); Webster's method; and the Australian method. Investigation of traffic signal upgrading strategies in the field can be expensive and time consuming. Unexpected and unnecessary congestion may result and cause negative citizen reaction. Many efforts have been directed towards the development and use of software computer models to evaluate the impacts of various strategies for upgrading traffic signals in different operating environments. The two most widely used packages that were developed to analyze and evaluate traffic operation at isolated intersections are the signal operations analysis package (SOAP) and the traffic experimental and analytical simulation package (TEXAS). For arterial streets, the methods that are commonly used in the timing design of fixed-time arterial systems include conventional methods, the maximal bandwidth method, and the delay/difference of offsets method. The two commonly used packages in the design and evaluation of signal operations at arterials are the progression analysis and signal system evaluation routine (PASSER II(80)) and the arterial analysis package (AAP). For a network that is comprised of a number of signalized intersections, the coordination of traffic signals along the route is regarded as one of the most efficient ways to improve total system performance by reducing delay, stops, fuel consumption, and vehicle emissions. Cycle length, splits, and offsets need to be evaluated and made optimum to improve total system performance. Since the manual work involved in designing the timing plans for a network is quite cumbersome and at times unmanageable, many efforts have been made to develop and use software packages that can assist traffic engineers in solving traffic and transportation management problems on grid networks. The two most widely used packages are TRANSYT and NETSIM. In response to the need to develop advanced operational control programs which would result in a marked improvement in traffic flow, extensive research and develop efforts have been directed towards traffic-responsive control strategies of urban street systems. This area represents one of the leading edges of the traffic control field. The methods that showed good promise to reach the desired goal are: the urban traffic control systems (UTCS); the splits, cycle and offset optimization technique (SCOOT); and the Toronto methods. These methods represent new concepts which could enhance the state-of-the-art in online control techniques.