TRB Research Circular E-C081: A Research Program for Improvement of the Highway Capacity Manual describes a research program designed to improve the Highway Capacity Manual (HCM). The proposed program was developed by the members of the TRB Highway Capacity and Quality of Service Committee with the assistance of feedback from users of the HCM. The program includes 38 research studies that would provide a means to permit improvements to the present HCM and upgrade future editions to meet user needs.