Estimating Interstate Highway Capacity for Short-Term Work Zone Lane Closures: Development of Methodology

Defining and understanding traffic flow parameters within short-term Interstate work zones are crucial in developing effective policies to manage construction and maintenance work conducted on the nation’s heavily traveled freeways. The South Carolina Department of Transportation (DOT) initiated a research study to develop a methodology for use in determining an updated lane closure policy for Interstate highway work zones. Phase 1 of the research was completed in May 2003, and findings identified threshold volumes for two-to-one lane closure work zone configurations. Phase 2 of the research further expanded numerically derived relationships and contained analysis of other short-term lane closure configurations including three-to-two and three-to-one lane closures. Both research phases concentrated on methods to determine the number of vehicles per lane per hour that can pass through short-term Interstate work zone lane closures with minimum or acceptable levels of delay as defined by South Carolina DOT. Phase 2 includes an expanded list of data collection sites with differing work zone characteristics. This paper presents the analysis and results of Phase 2 of the research. Headway analysis revealed that passenger car equivalents (PCEs) differed for various speed ranges and modified PCEs for various speed groups were applied in calculating capacity. A model for calculating work zone capacity that incorporates base capacity, PCEs for various speed groups, adjustment factors related to specific work zone characteristics, and number of lanes open through the work zone, is recommended.