Highway Capacity Analysis After Highway Capacity Manual 2000

The publication of the “fourth” full edition of the Highway Capacity Manual (HCM) in the fall of 2000 represented a major step forward in state-of-the-art highway capacity and quality-of-service analyses. Even as this major step is taken, however, old issues reemerge and new ones arise as to the core concepts involved, the directions that such analyses should take in the future, and the needs of HCM users. Now that HCM has begun to address system and multimodal measures, the nature and meaning of capacity and level-of-service concepts need to be reexamined. The role of simulation must be more clearly defined, as must the limitations of more conventional highway capacity analyses. As databases improve, the question of statistical accuracy and stochastic variations in standard measures may seem more important, even though the inherent variability in traffic flow characteristics remains essentially unchanged. The need for software to implement ever more complex methodologies raises additional issues. As the Committee on Highway Capacity and Quality of Service and its members consider these and other important issues, an attempt to outline the major issues and alternatives that should be examined is made. In addition, some suggestions as to potential paths to follow are provided.