About the Highway Capacity Manual
The Highway Capacity Manual (HCM) provides methods for quantifying highway capacity. It serves as a gold standard and fundamental reference on concepts, performance measures, and analysis techniques for evaluating the multimodal operation of streets, highways, freeways, and off-street pathways.
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. HCM is being published by the Transportation Research Board of National Academy of Sciences.
7th Edition of HCM (2022)
The 7th Edition of the Highway Capacity Manual (HCM 2022) provides the analysis of Connected and Automated Vehicles (CAVs) for planners to envision future scenarios with certain levels of CAVs in the traffic mix. This addition makes this reference material distinctive as it serves as the only reference material to enable such analysis. These are highlights of new changes in this release of the HCM:
- Analysis of Connected and Automated Vehicles (CAVs) for freeways, roundabouts, and signalized intersections.
- Brand new two-lane highways method
- A revised pedestrian method for signalized intersections with two-stage crossing, two-leg crossing closed pedestrian crossing, exclusive pedestrian phases, and more.
- New Active Traffic and Demand Management (ATDM) for urban streets analysis framework to include effects of non-recurring sources of congestion in scenario assessment.
- New network method to enable assessing the freeway lane-by-lane operation as well as estimating the impact of arterials operation on freeways and vice versa.
Beyond HCM 7th Edition (“HCM 7.1”)
The team at McTrans Center is actively involved in the development of new research for future editions of the Highway Capacity Manual, so these methods can be timely implemented in HCS. In 2024, the Highway Capacity and Quality of Service Committee at TRB (ACP40) peer-reviewed and approved the following new HCM draft chapters:
- Chapter 13 – Freeway Weaving Segments
- Chapter 14 – Freeway Merge and Diverge Segments
- Chapter 27 – Freeway Weaving: Supplemental
- Chapter 28 – Freeway Merge and Diverge: Supplemental
These revised chapters include updated methodologies for analyzing merge, diverge, and weaving segments based on the research project NCHRP 07-26. One of the major changes in the NCHRP report is the reduction of capacity density to 35 pc/mi/ln. Starting with the HCS 2025, users can choose between the HCM 7 or HCM 7.1 methodologies for their analyses.
