The Revised Highway Capacity Manual’s Freeway Weave Segments Analysis

Project K2 (Assessing and Addressing Deficiencies in the HCM Weaving Segment Analyses; Principal Investigator: Dr. Behzad Aghdashi, NCSU)

Dr. Behzad Aghdashi of North Carolina State University is the lead researcher in a STRIDE funded project that is looking at deficiencies in the Highway Capacity Manual’s (HCM) weave segment analysis. As weave segments are one of the most complex segment types in a freeway system, he and co-principal investigator, Dr. Lily Elefteriadou, professor and director of the University of Florida Transportation Institute and the STRIDE Center, set out to create a better methodology.

The Highway Capacity Manual (HCM) is a widely used reference material for evaluating the performance of the surface streets and contains information on how to evaluate weave segment operations. However, it has been found that this feature has some inconsistencies. For example, the speed of a vehicle weaving in and out of traffic is being reported as higher than those vehicle that are traveling a steady course. Another discrepancy is that the current method used in the HCM is insensitive to short length segments.

This project used data collected from past projects as well as new data collected via drone during the course of this project. The video data collected from a drone was analyzed by the research team’s graduate students and summarized into a set of numerical observations. These data then fed into a regression model to generate the speed flow model for the weave segments. The research team validated the proposed models by implementing them into a separate dataset and comparing the estimated speed to the empirical speed observations. The results show the faithful estimation of the weaving segments’ speed via the proposed method.

The proposed method is much less complex compared to the current HCM method and is easier to implement and calibrate. The new model can potentially be adapted to be included in HCM and subsequent software packages that are using HCM methods for various analyses. The researchers believe that transportation professionals who are currently using the HCM models to assess the operation of freeway systems can largely benefit from this new methodology.