Level of Service Analysis of Freeway Weaving Segments

This paper reports on the product of NCHRP Project 3-75, which resulted in the development and calibration of new models for freeway weaving segments, including a draft chapter for the forthcoming Highway Capacity Manual (HCM). The most critical element of the current procedures in the HCM 2000 is the prediction of the average speeds of weaving and nonweaving vehicles in the weaving segment. These speeds are converted to an overall density for the segment that determines the prevailing or expected level of service. The proposed method does away with the strict assignment of weaving geometries to one of three configuration categories and also the need to determine whether the operation of the weaving segment is constrained or unconstrained. That approach led to the need to calibrate 12 equations to predict speeds. In research, this greatly increased the size of the desirable database for calibration. The new approach relies on the prediction of lane-changing activity within the weaving segment to quantify the impact of configuration and type of operation on resulting speeds and densities.