Research has shown that area population, the number of lanes in the lane group, and speed limit are correlated with saturation flow rate. However, the procedures in Chapter 16 of the 2000 Highway Capacity Manual (HCM) do not recognize these influences. The objective of this paper is to report the findings and conclusions from a research project that examined the influence of these and other factors on the saturation flow rate of the through lane group at several signalized intersections. An examination of several thousand headway observations indicates that saturation flow rate increases in a predictable way with an increase in population, number of lanes, or speed limit. Several saturation flow rate adjustment factors are calibrated on the basis of field data and are recommended for inclusion in the next edition of the HCM.
effect (e.g., left-turning truck movements). Upon future field data collection and validation, the subgroup model could be used to evaluate the appropriateness of the multiplicative saturation flow rate model that is implicit in the HCM, a model that is increasingly scrutinized.Practical applications of the subgroup method that cannot be performed by traditional HCM procedures include • Individual lane queuing analyses [which could incorporate the queuing model implemented in the 2000 HCM (5)], • Delay estimates by vehicle type for conducting emissions analyses, and • Evaluation of measures of effectiveness (MOEs) for approaches that experience prepositioning effects due to downstream conditions.This paper presents a framework for estimation of subgroup saturation flow rates at signal-controlled intersections. The framework is founded upon the procedures described in the 1997 HCM. The framework is intended to serve as an extension to the HCM method by providing performance results beyond the level of the lane group. The following sections describe the development of the subgroup method. The paper concludes with a numerical example that compares the saturation flow rates for three example calculations found in the 1997 HCM by use of the subgroup method and existing HCM procedures. The intent of the numerical examples is to demonstrate the validity of the methodology when it is applied by using the same assumptions used in the HCM.
The information contained in this document was taken directly from the submission of the authors. This document has not been edited by the Transportation Research Board. Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.