The Iowa Department of Transportation (Iowa DOT) sponsored the Center for Transportation Research and Education (CTRE) conduct of research on the capacity and driver merge behavior at Interstate work zone merge areas. The principle goal of this research is to determine the traffic capacity at work zone locations where two lanes of traffic are reduced to one (lane closure). Reducing two traffic lanes to one in each direction is the typical method of channeling traffic into a work zone on Iowa's rural Interstate system. When traffic volumes exceed the capacity of these merge points, the resulting congestion can lead to the formation of queues, which result in delays and increases the potential for traffic crashes. Successful implementation of work zone improvements at locations where congestion is expected will provide a benefit to motorists through reduced delays and increased safety. The research project was conducted in four phases: a literature review, the collection of traffic data at work zone merge areas, the analysis of this data, and the development of a computer simulation tool to model traffic at merge areas.

Research was performed to determine total costs (construction and road user costs) and safety impacts associated with traffic control through work zones on rural four-lane, divided highways using single lane closure (SLC) versus two-lane, two-way traffic operations (TLTWO). An informational guide for use in selecting cost-effective traffic control strategies for proposed construction projects was also prepared. Construction data were collected from 51 construction projects in 11 States, and traffic capacity delay studies were conducted at 25 projects in 10 States. Guidelines are presented in this report for selection of the best traffic control alternative between SLC and TLTWO. A simplified procedure to estimate road user costs for SLC and TLTWO traffic control strategies is also included. This guide is Volume II of a two-volume series. Volume I (FHWA-RD-89-209) is the final report.