ABSTRACT
The work zone capacity in freeways is usually defined as the mean queue discharge flow rate at a freeway work zone bottleneck (any constricted location that restricts the flow of
vehicles in a work zone) (HCM 2000). Work zone capacity has a significant impact on the congestion and traffic queue delays which result in increased driver frustration, increased traffic accidents, increased road user delay cost, and increased fuel consumption and vehicle emissions. Highway agencies often use the empirical and highly
approximate method described in the Highway Capacity Manual (HCM) (HCM 2000) to
determine the freeway work zone capacity with lane closures. The HCM provides a base capacity of 1,600 vehicles per hour per lane (vphpl) for short-term ideal unrestricted highway work zones. Guidelines are given on how to modify the base value to take into
account percentage of trucks, work intensity, proximity of ramps, and lane widths. However, a large number of additional factors affect the freeway work zone capacity
estimation which are neglected in the HCM guidelines.
