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HCM 7.1 for Freeway Analysis is Here!

The Highway Capacity Manual was updated in December 2025 to incorporate new research on freeway merge, diverge, and weaving segment analysis. The research project developed a new methodology and provided replacement HCM chapters that were subsequently revised and are now available for free on the National Academies website. The new chapters are known as HCM 7.1 to distinguish them from the original 7th edition chapters.

The previous methods for ramp junctions and weaving segments were developed separately so for certain combinations of traffic volumes and roadway geometry, you could get unexpected results. For example, the before condition with a merge segment followed by a diverge segment might show better performance than the after condition where an auxiliary lane is added to form a weaving segment. The new research was based on a much larger sample size, used modern sensor data, and included more ramp configurations than the research used to develop the previous method.

The new methodology starts with determining the performance measures for an equivalent basic freeway segment: that is, a segment without ramps. A speed impedance term due to the merge, diverge, or weave condition is then subtracted from the basic segment speed to determine the analysis segment’s speed. If the ramp volume is zero, then speed impedance is also zero, and the segment performs the same as the equivalent basic segment.

The researchers found that the critical density, the density at capacity, occurred at about 35 passenger cars per lane per mile (pc/ln/mi) in the new data set. This is lower than previous weaving capacity of 43 pc/ln/mi. The previous method did not have a capacity threshold for density for merge and diverge segments. Since capacity represents the threshold between level of service (LOS) E and F, the LOS thresholds were revised as shown in the table below. These new thresholds match those for basic freeway segments for LOS A and B but have narrower ranges for LOS C through E.

The new methods are simpler but use the primary inputs from the previous methods. Merge and diverge segment performance is based on the number of freeway lanes, the mainline and ramp volumes, ramp speed, and the ramp acceleration or deceleration lane length. Weaving segment performance depends on number of freeway lanes, weave lanes, and lane changes; the origin-destination volumes; and the weave type.

Here are some additional notable changes.
- Merge and diverge segments can be as long as the acceleration or deceleration lane even if the length is greater than 1,500 feet.
- The presence of adjacent ramps no longer affects the performance of merge and diverge segments.
- The density for the ramp influence area is no longer calculated. The density for merge and diverge segments applies to all lanes.

If your reviewing agency is not familiar with the HCM 7.1 methods, it’s a great opportunity to let them know.

Highway Geometric Design Explained

Highway geometric design plays a critical role in ensuring safe, efficient and comfortable movement of traffic. It focuses on the physical layout of roads based on speed, terrain, traffic volume and safety requirements.

Key Elements of Highway Geometric Design …

Designing for Safe Speeds supplements GDCI’s Global Street Design Guide
(GSDG), which sets a new global standard for designing urban streets that
prioritize people. This guide builds on the existing GDCI publications on
holistic street design and emphasizes speed management, one of the most
critical factors in reducing traffic violence and saving lives. In line with GDCI
work it maintains a comprehensive approach to help cities create safer,
more livable streets for everyone. Though it can be used as a stand-alone
document, Designing for Safe Speeds is best applied in combination with the GSDG, as it references key principles from the original guide, alongside other GDCI resources. Funded by Bloomberg Philanthropies, this document will inspire leaders, inform practitioners, and empower communities to advocate for and implement changes in streets and networks towards safe speeds, while helping achieve cleaner air, increased mobility, more physical activity, and other sustainability and livability goals. This guide aims to:
• Highlight the life-saving and social impact of designing streets for safe
speeds.
• Promote safer, more people-centered streets by addressing speed and car
dominance through practical strategies.
• Share tools, strategies, examples of street designs, and case studies from
around the world that can be adapted to local contexts.
• Provide clear speed management recommendations through effective
street design and operational solutions for urban contexts.

Global Street Design Guide - Global Designing Cities Initiative The Global Street Design Guide is supporting practitioners to redefine the role of streets in cities around the world. Created with the input of experts from 72 cities in 42 countries, the Guide offers technical details to inform street design that prioritizes pedestrians, cyclists, and transit ride...

https://highways.dot.gov/safety/intersection-safety/intersection-types/roundabouts

Roundabouts | FHWA Source:JamesB

NCHRP Synthesis 652: Traffic Capacity Level of Service - Adaptations and Usage.

The level of service (LOS) concept has been used for over 50 years by state departments of transportation (DOTs) in the U.S. for policy setting, planning, analysis, and communication efforts. Adoption of the LOS framework by individual state DOTs has generally been consistent with the Highway Capacity Manual, although usage and application may vary across different state DOTs.

NCHRP Synthesis 652: Traffic Capacity Level of Service: Adaptations and Usage, from TRB's National Cooperative Highway Research Program, includes findings that may assist state DOTs in improving their LOS practices and policies.

Read "Traffic Capacity Level of Service: Adaptations and Usage" at NAP.edu Read chapter Front Matter: The level of service (LOS) concept has been used for over 50 years by state departments of transportation (DOTs) in the U.S. fo...

📖 Recent NCHRP Synthesis report 📚

NCHRP Synthesis 650: Practices for Operational Traffic Simulation Models.

https://nap.nationalacademies.org/catalog/29076/practices-for-operational-traffic-simulation-models

Designing Interchanges

An interchange consists of the through motorway, the slip roads and the crossroad.

1. Through motorway design
- Spacing
- Basic Number of Lanes
- Auxiliary Lanes
- Lane Reduction

2. Slip Road/Ramp Design
- Design Speed,
- Profile,
- Sight Distance,
- Distance Between Successive Exits

3. Entrance/Exit Slip Road Design
- Entrance/Exit Sight Distance,
- Exit Design Speed,
- Entrance Design Speed,
- Entrance/Exit Designs,
- Entrance/Exit Locations,
- Entrance/ Exit Grades,
- Exit Profiles,
- Entrance Profiles,
- Exit Slip road Transitions

4. Slip Road/Ramp Terminal Design
- Terminals
- Terminal grades
- Terminal lications
- Terminal Signt Distances

Designing Interchanges An interchange consists of the through motorway, the slip roads and the crossroad. Spacing - Minimum interchange spacing is determined by weaving volumes, ability to sign, signal progression, and required lengths of speed change lanes.

The Rural Road Safety Awareness Week. FHWA is encouraging State DOTs and local transportation agencies to make the commitment to reduce severe crashes on rural roadways by implementing FHWA’s Proven Safety Countermeasures and National Highway Traffic Safety Administration NHTSA's 𝘊𝘰𝘶𝘯𝘵𝘦𝘳𝘮𝘦𝘢𝘴𝘶𝘳𝘦𝘴 𝘵𝘩𝘢𝘵 𝘞𝘰𝘳𝘬. Find out more here:

https://highways.dot.gov/safety/proven-safety-countermeasures

https://highways.dot.gov/safety/proven-safety-countermeasures/proven-safety-countermeasures-rural-communities-resource

https://www.transportation.gov/rural/traffic-safety-countermeasures

Proven Safety Countermeasures | FHWA Secure .gov websites use HTTPS A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

The development of HDM5 is officially underway ...

Global Development of the HDM-5 Platform Officially Underway The Highway Development and Management (HDM) Model has been a cornerstone tool for road agencies worldwide since its inception in 1968. Critical for road development and maintenance for 1,500 organizations in 100 countries, HDM supports investment planning, maintenance prioritization, and economic e...

OVERSEAS ROAD NOTES - the Series

https://www.trl.co.uk/projects/overseas-road-notes---the-series