The study and analysis of unsignalized and signalized intersections is a topic that is of vital concern to the transportation engineer today.  The expanded theoretical knowledge base of traffic flow at unsignalized and signalized intersections and the greatly improved computer software and hardware systems now widely available have combined to improve the capability of a very important tool for the transportation engineer, the computer simulation model.  These computer models are much more crucial today since the kind of problems that transportation engineers are required to solve are much more complex than in the past.  This results from several factors. 

First, the level of traffic congestion in many urban areas has increased significantly from previous years.  The peak hour is now in many cases the peak three hours, with congested conditions often affecting not just one intersection, but whole arterials and networks.  Thus, the engineer must account for conditions not just in one place (at one intersection) or one point in time (the standard 15-minute analysis period), but over large blocks of both time and space. 

Second, control technology is now so complex that new models are needed that can take into account the dynamic and adaptive control schemes that are now available.  This new technology is embodied in the Intelligent Transportation System, or ITS, initiative that is now being promoted by the United States Department of Transportation.  Even in some of the lower density areas or smaller urban areas found in the inland Northwest, congestion is increasing.  The City of Moscow is now experimenting with video detection techniques to monitor and control signalized intersections.  The cities of Coeur d'Alene, Spokane, and Boise are all implementing advanced technologies to monitor and control complex signalized intersection networks.