Objective: The objective of this effort was to develop improved methods for capacity and quality-of-service analyses of weaving areas.
Status: Complete. The research results were not included in the HCM 2000 because the proposed methodology is controversial. They should, however, be beneficial to other researchers studying this issue.
Product Availability: The contractor's revised final report is available here.
Background: A user survey conducted under NCHRP Project 3-55 indicated that one of the strongest user needs for the Year 2000 of the Highway Capacity Manual (HCM) was the inclusion of information and methodologies to analyze arterial weaving areas. There was also an indication that the 1997 Chapter on freeway weaving needed to be updated, particularly with new operational data from the field or simulation models. This updating was considered important because the 1997 chapter is based on data that are now 12 to 30 years old. Facilities that operate between freeways and arterials, such as collector-distributor roads and frontage roads, should also be included in the study of weaving operations.
Tasks: The research consisted of the following tasks: (1) Conduct a comprehensive review of (a) methods in common use for analyzing weaving areas, and (b) weaving-related research. Assess each method's structure and underlying assumptions, and identify its shortcomings and strengths. (2) Propose one or more conceptual models to analyze weaving areas on freeways, arterials, collector-distributor roads, and frontage roads. The model(s) should consider critical factors that affect weaving operations such as weaving length, lane configuration, traffic volumes, and upstream influences. The model(s) must produce descriptive performance measures consistent with the recommendations from NCHRP 3-55(4). Terminology should be consistent with current HCM definitions. The model(s) should be applicable to planning, design, and operational analyses and robust enough to handle a wide range of conditions, including oversaturated conditions. (3) Assess the applicability and validity of existing traffic simulation models for analysis of weaving areas. Determine if simulation models could be a viable source of weaving area data for this project. (4) Prepare an interim report that contains the results of Tasks 1 through 3 and a revised work plan for Phase II. The revised work plan should include a complete data collection plan for Task 5 that addresses availability of existing data; additional data to be collected in the field and, possibly, through simulation; minimum sample size for desired accuracy; site selection; collection methods; and data reduction methods. (4.5) Review existing field data from up to twelve sites, simulate those sites using FRESIM, and calibrate FRESIM to replicate the field data. Prepare an addendum to the interim report comparing the field and simulated data and field-measured capacity flows and those predicted by the postulated capacity model. The addendum will include recommendations for additional field data collection. (5) Collect and reduce the data in accordance with the approved data collection plan. (6) Based on the Task 2 conceptual model(s) and using the data from Task 5, develop proposed analytical methods for incorporation into the HCM 2000 that balance the needs for simplicity and accuracy. Assess the performance of the methods over a realistic range of values for input variables. Determine the accuracy of the performance measure estimates produced by the method(s). (7) Prepare new material on freeway, arterial, collector-distributor road, and frontage road weaving for inclusion in the HCM, including the following: (a) thresholds for levels of service that are consistent with other relevant methods in the HCM, (b) sample problems, and (c) multimedia material. (8) Prepare a final report that documents the entire research effort and includes the HCM material as a stand-alone appendix.