The Highway Capacity Manual HCM, sixth edition provides methods for quantifying highway capacity. In its current form, it serves as a fundamental reference on concepts, performance measures, and analysis techniques for evaluating the multimodal operation of streets, highways, freeways, and off-street pathways. The sixth edition incorporates the latest research on highway capacity, quality of service, active traffic and demand management, and travel time reliability and improves the HCM's chapter outlines. The objective is to help practitioners applying HCM methods understand their basic concepts, computational steps, and outputs. These changes are designed to keep the manual in step with its users' needs and present times.
HCM has evolved over the years to keep pace with the needs of its users and society, as the focus of surface transportation planning and operations in the United States has moved from designing and constructing the Interstate highway system to managing a complex transportation system that serves a variety of users and travel modes. Providing mobility for people and goods is transportation's most essential function. It consists of four dimensions:
- Quantity of travel, the magnitude of use of a transportation facility or service;
- Quality of travel, users' perceptions of travel on a transportation facility or service with respect to their expectations;
- Accessibility, the ease with which travelers can engage in desired activities;
- Capacity, the ability of a transportation facility or service to meet the quantity of travel demanded of it.