About the research
The Highway Capacity Manual (HCM), Sixth Edition, introduces a new methodology to estimate freeway work zone capacity. For basic freeway segments, the methodology estimates the work zone pre-breakdown capacity and queue discharge rate by accounting for the effects of lane closure type, barrier type, area type, lateral clearance, and lighting. The methodology also provides a means to predict free-flow speed in work zones based on speed limits (both normal statutory and reduced work zone limits), lane closure type, barrier type, lighting, and total ramp density. For special work zone configurations, such as those involving merge, diverge, and weaving maneuvers, or work zones with directional crossovers, adjustment factors are provided for queue discharge rates. But no adjustment factors were provided to adjust free flow speeds estimates.
The data used to develop the HCM work zone capacity methodology were collected in 12 work zone sites with different configurations across six states, including Virginia, California, Maryland, Nevada, Arkansas, and Arizona. It is expected that capacity at work zones in the SWZDI states might be significantly different from the states where the data were collected. Thus, it is crucial to validate the HCM methodology using locally collected data and provide adjustment factors as necessary. In addition, for the special work zone configurations the queue discharge rate adjustment factors were derived from field-calibrated microsimulation models. Validating these factors using data collected at merge, diverge and weaving segments would shed light on the applicability of the simulated results to SWZDI states.
The objective of this project is to validate the HCM work zone capacity methodology for urban and rural freeways in the SWZDI states and to develop adjustment factors that produce more accurate estimates of work zone capacity as compared to the default HCM values. The study will utilize archival work zone data, as well as new field data collected at a diverse range of sites to validate and calibrate these analysis tools.