Improvement of existing highway systems, such as maintenance, rehabilitation, and reconstruction, is accompanied with lane closure at work zones. Such lane closure causes road user costs for traffic congestion and delays at the work zones. A robust method is developed in this research to support strategic decisionmaking on lane closures. At this stage, the research focuses on a common situationclosing a segment of one lane in one direction on a four-lane highway. The method divides a work zone into arriving-, entering-, passing-, and leaving-zone and classifies the flow of vehicles as arriving-, in-, through-, and out-flow. Thereby, it accounts for traffic congestion and delay due to speed reduction, upstream queue, and speed recovery. Based on dynamic simulation technique, the method simulates the flow of vehicles and measures congestion and delay at work zones. The new method would benefit engineers in planning highway system improvement projects.