Modeling Framework for Capacity Analysis of Freeway Segments: Application to Ramp Weaves

Abstract

This research proposes a new modeling framework for the analysis of freeway segments. The framework provides a continuum from the operation of ramp weave segments to an equivalent basic segment serving the same traffic with the same number of lanes and free-flow speed. This approach distinguishes between congestion effects caused by high v/c ratios from turbulence caused by merging, diverging, and weaving traffic, thus greatly simplifying the model form, and its extensibility to other freeway segment types. The paper presents an application of this new framework to the analysis of ramp weaves, which were not sufficiently sampled in the development of the HCM6 methodology. The proposed model is shown to be superior to the HCM6 method both in relation to explaining field observations of speeds and in its simplicity in application. The results include a new formula for capacity estimation that is highly sensitive to segment length, and a speed estimation model that converges for low weaving volumes or at very high weaving segment lengths to that observed at a basic segment. Because the proposed model is calibrated with data mostly from North Carolina, it is recommended that data at additional sites be included in a larger calibration effort to ensure its applicability to a broader set of weaving segment configurations.