The development and validation of a digital simulation model for design of freeway diamond interchanges. Presented at the Twenty-Ninth National Meeting of the Operations Research Society of America, May 18-20, 1966.

Sections I and II of this paper are devoted to a brief description of the aims and implementation plans of the project. The remainder, and by far the major portion of the paper, describes the completed work on version 1 of Model 1. The principal goal of the project is to develop a valid general-purpose simulation model of a diamond interchange for traffic between a freeway and an arterial street. The existence of such model will enable the traffic engineer to study the effects of alternative geometric and control configurations on diamond interchange operations. The principal imposes of this study is on the validation problem. To validate the model efficiently, the complete interchange is separated into components one of which, for example, is the merging of an on-ramp with the freeway. A computer model is then designed for that component, and its performance (when the parameters are properly set) is compared with that of existing real operations. If realistic performance is obtained, the next component of the interchange is then added; otherwise, indicated modifications of the model are made and again compared with field data. This iterative process is continued until validation is achieved for the entire interchange model. A major goal is to develop a model whose running time on the computer is substantially less than the simulated time. This is of importance because of lengthy simulation times required to achieve statistical reliability of simulated vehicular performance. To achieve such efficiencies, it is essential to aggregate many details of system operation so that macroscopic (as opposed to microscopic) simulation techniques may be used. Model validation requires the consideration of the methods of data collection as well as the determination of significant differences (if any) between the simulated and real world. A description is given of the data collection techniques used for the preliminary validation study as well as the techniques to be used in the ultimate validation study. Also included is a discussion of the statistical problems involved in comparing model performance with that of actual traffic flow. An account is given of the work accomplished to date. This model, as well as its data reduction programme, has been programmed, debugged, and is running. Some of the results obtained with it are described as are the results of the preliminary validation study.