National Academies Press: OpenBook
Page iv
Suggested Citation:"ABSTRACT." Transportation Research Board. 1996. Capacity Analysis of Traffic-Actuated Intersections: Final Report. Washington, DC: The National Academies Press. doi: 10.17226/6347.

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ABSTRACT The 1985 Highway Capacity Manual (HCM) prescribes a methodology in Chapter 9 for estimating the delay and level of service at a signalized intersection as a function of the traffic characteristics and the signal timing plan. This methodology is widely used both nationally and internationally and approaches a standard for the evaluation of the performance of signalized intersections in the U.S.A. The present treatment of traffic-actuated control in the HCM leaves much room for improvement. The limitations ofthis treatment win be the main target ofthe research described in this report. These limitations are largely the result of an oversimplified approach to analysis that has not kept pace with the rest of HCM Chapter 9. The work that was carried out under NIP Project 3-48 included the formulation of an improved methodology for predicting the operating characteristics oftraffic-actuated control, and for estimating the delay and level of service associated with a given set of operating parameters. The principal product of this research was an improved model set in a computational framework that facilitated testing ofthe model, and will eventually become a tool for the end user. The testing and evaluation of the methodology relied heavily on simulation, augmented by limited field studies. Based on the findings presented in this report, it is suggested that the traffic-actuated control analysis methodology developed in connection with this project is valid and satisfies the project objectives. The signal timing estimation model has demonstrated a clear superiority over the status quo. Of particular importance are the model features that make it sensitive to the traffic-actuated controller settings, the free queue phenomenon and the coordinated control mode. The combination of these features gives the model capabilities that are needed by the analyst and cannot be found together in any other technique. NCHRP Project 3-48 Final Report: Page iii

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