Computer Simulation for Traffic Control

Rosenblueth and Wiener1 stated in 1945, “No substantial part of the universe is so simple that it can be grasped and controlled without abstraction. Abstraction consists in replacing the part of the universe under consideration by a model of similar but simpler structure. Models . . . are thus a central necessity of scientific procedure.” Models can take on many forms ranging from a simple rule of thumb to a complex mathematical representation. At times, it is neces­ sary to perform a digital simulation utilizing a simulation model. This approach may be required for several reasons. First, the system under consideration may be so complex that it is not possible to model it in terms of a set of mathematical equations for which analytic solutions can be derived which predict system be­ havior. Most systems that exhibit pronounced non-linear behavior fall into this class. Second, even though mathematical modeling of the system may be possible, it may not be possible to obtain an analytic solution to the problem, and thus a simulation may be necessary to predict future be­ havior of the system. Third, in many cases, it is either physically impossible or economi­ cally unfeasible to perform experimental testing and development. For example, design and development of a spacecraft to meet rigorous reliability and performance specifications required a great deal of knowledge regarding human capabilities in a strange environment— knowledge that was not available before the first manned space flights. One way of obtaining the required data was to experiment using human pilots in actual test conditions. Obviously, this method is not acceptable by the standards of safety established in our space program. However, NASA manned spaceflight center performed large numbers of simulated flights to ascertain system effectiveness and