CAPACITY OF FREEWAY WORK ZONE LANE CLOSURES

The Iowa Department of Transportation (DOT), like many other state transportation agencies, is experiencing growing congestion and traffic delays in work zones on rural interstate highways. The congestion has resulted from unprecedented growth in traffic on rural segments of Iowa interstates. Traffic volumes have reached levels that are unlike those experienced in the past. The congestion on rural interstates is particularly problematic because in rural areas there are few, if any, parallel diversion routes and through traffic, traveling long distances, may be relatively unfamiliar with local conditions and alternative routes. In addition, drivers are generally unaware of the work zone and do not expect heavy congestion in rural Iowa. The congestion results in unproductive and wasteful delays for both motorists and commercial vehicles. It also results in hazardous conditions where vehicles, stopped in queues on rural interstate highways, are being approached by vehicles upstream at very high speeds. The delay also results in driver frustration, making some drivers willing to take unsafe risks in an effort to bypass delays. To reduce the safety hazards and unproductive delays of congested rural interstate work zones, the Iowa DOT would like to improve its traffic management strategies at these locations in the future. During the summer of 1998 the Center for Transportation Research and Education (CTRE) at Iowa State University observed a work zone on a rural Iowa interstate highway to measure the volume of vehicles that can pass through a work zone lane closure prior to and during congested operations and to better understand related driver behaviors. This paper reports on the part of the research that was done by CTRE for the Iowa DOT to evaluate the capacity of lane closures and driver behavior.