Evolution of HCM methodologies

Dr. Fabio Sasahara

The first Highway Capacity Manual was released in 1950 by the Bureau of Public Roads (the predecessor agency to the FHWA) and has been, for decades, the gold standard for evaluating the level of service of several road types.

Since then, the HCM has undergone a major update every couple of years to keep up with the evolving needs of the transportation profession. The Highway Capacity Software (HCS) was first released in 1987, based on the HCM 3rd Edition, and has been updated yearly.

Timeline of HCM and HCS Releases

Every time the HCM goes through a major update, so does the HCS, as it incorporates the most current methods to evaluate the Level of Service (LOS) of different types of roads. This article provides a recap of the major methodological changes in the manual since HCM2000 – if you are not using the latest HCS release, you may be missing out on several features included in the HCM over the last years.

HCM 2010 (2010)

The HCM 2010 release, incorporated in HCS2010, made significant advances in multimodality, adding new methods to evaluate LOS for pedestrians, bicycles, and transit. It also significantly improved the procedures for urban streets, including: evaluation of actuated signals; a new method for roundabouts, a new method for interchange ramp terminals, and a new method to evaluate urban street segments bounded by intersections.

HCS 2010 Main Menu

SYSTEM ELEMENT	DESCRIPTION
Freeway Facilities	New weaving segment methodology ⁽¹⁾ New LOS threshold for facilities Updates on the impact of weather and work zones Improved prediction method for free-flow speed
Multilane Highways	New bicycle LOS methodology
Two-Lane Highways	Two-direction analysis replaced with a one-direction approach New bicycle LOS methodology
Urban Street Segments	New HCM chapter⁽²⁾ (Urban Street Facilities) with a methodology to aggregate results from multiple segments New methodology for urban streets segments⁽²⁾, including free-flow speeds, running times and stop rates
Signalized Intersections	New modeling procedure for actuated control⁽²⁾ Improved methods to calculate control delay, including coordinated arrivals, protected-permitted left turns and sneakers⁽²⁾ New pedestrian and bicycle LOS methodologies⁽³⁾
TWSC	Added gap-acceptance parameters for six-lane streets⁽²⁾
AWSC	Added a queue-estimation model⁽²⁾
Roundabouts	Added new LOS table; new methodology to evaluate LOS for roundabouts⁽⁴⁾
Interchange Ramp Terminals	New methodology to evaluate interchange ramp terminals⁽⁵⁾ (Diamond, Parclo, SPUI)

⁽¹⁾ NCHRP 3-75: Analysis of Freeway Weaving Sections; ⁽²⁾ NCHRP 3-79: Measuring and Predicting the Performance of Automobile Traffic on Urban Streets; ⁽³⁾NCHRP 3-70: Multimodal Level of Service Analysis For Urban Streets; ⁽⁴⁾ NCHRP 3-65: Applying Roundabouts in the United States; ⁽⁵⁾NCHRP 3-60: Capacity and Quality of Service of Interchange Ramp Terminals;

HCM 6th Edition (2016)

The HCM 6th Edition, titled “A Guide for Multimodal Analysis”, continued the trend to become a more multimodal standard. It introduced new methods for Travel Time Reliability analyses for freeways and urban streets and significantly increased the capabilities of the Freeways procedures, including work zones, managed lanes and more accurate factors for the effects of trucks. On the urban streets side, the capacity equations for roundabouts were recalibrated yielding significantly higher capacities; new methods for alternative intersections were also included in the manual.

HCS 7 Main Menu

SYSTEM ELEMENT	DESCRIPTION
Freeways	New method to better evaluate the effects of trucks⁽⁶⁾ New method to evaluate work zones⁽⁷⁾ New methods to analyze managed lanes⁽⁸⁾ New methods for Travel Time Reliability analyses⁽⁹⁾
Multilane Highways	Speed-flow equation modified to be consistent with Freeway Basic Segments
Two-Lane Highways
Urban Streets	New methods for Travel Time Reliability analyses⁽⁹⁾ New threshold for LOS A
Signalized Intersections	New saturation flow rate adjustment for work zones and midsegment lane blockage
TWSC
AWSC
Roundabouts	Recalibrated models, yielding about 30% additional capacity compared to 2010⁽¹⁰⁾ New method to evaluate corridors with roundabouts⁽¹¹⁾
Ramp Terminals and Alternative Intersections	New methods for DDIs, RCUT, MUT and DLT intersections⁽¹²⁾

⁽⁶⁾ NCFPR 41 – Incorporating Truck Analysis into the Highway Capacity Manual; ⁽⁷⁾ NCHRP 03-107 – Work Zone Capacity Methods for the Highway Capacity Manual; ⁽⁸⁾ NCHRP Analysis of Managed Lanes on Freeway Facilities; ⁽⁹⁾ SHRP 2 L08 – Incorporation of Travel Time Reliability into the Highway Capacity Manual; (¹⁰) FHWA TOPR 34: Accelerating Roundabout Implementation in the United States; ⁽¹¹⁾ NCHRP 03-100: Evaluating the Performance of Corridors with Roundabouts; ⁽¹²⁾ FHWA TOPR2: Guidance for Alternative Intersections;

HCM 7th Edition (2022)

The HCM 7th Edition, implemented in the HCS2022 release, brought significant improvements to pedestrian LOS methods to better evaluate the effects safety and comfort aspects. Procedures for urban streets and signalized intersections were revised and the TWSC methodology was replaced with a brand new procedure with a new service measure. New additions to the manual also included adjustment factors to evaluate the impacts of Connected and Automated Vehicles (CAVs) and a new method (“Network Analysis”) to evaluate corridors with freeways and urban streets, including traffic interactions between these two distinct elements.

HCS 2024 Main Menu

SYSTEM ELEMENT	DESCRIPTION
Freeways	Capacity adjustment factors for the presence of CAVs⁽¹³⁾
Multilane Highways
Two-Lane Highways	New methodology to evaluate LOS for two-lane highways⁽¹⁴⁾, completely replacing the HCM6 methods
Urban Streets	Enhanced pedestrian LOS methods⁽¹⁵⁾
Signalized Intersections	Capacity adjustment factors for the presence of CAVs⁽¹³⁾ Enhanced pedestrian LOS methods⁽¹⁵⁾
TWSC	New pedestrian LOS methods⁽¹⁵⁾, with a brand new service measure Several corrections on equations for conflicting flow rates, capacities of lower rank movements and shared lanes
AWSC
Roundabouts	Capacity adjustment factors for the presence of CAVs⁽¹³⁾
Ramp Terminals and Alternative Intersections
Other	New “Network Analysis” ⁽¹⁶⁾ method to evaluate corridors comprised of freeways and urban streets

⁽¹³⁾ FHWA pooled fund study [TPF-5(371)]: Developing Highway Capacity Manual Capacity Adjustments for Connected and Autonomous Vehicle under Varying Levels of Volume and Market Penetration; ⁽¹⁴⁾ NCHRP 17-65: Improved Analysis of Two-Lane Highway Capacity and Operational Performance; ⁽¹⁵⁾ NCHRP 17-88 – Enhancing Pedestrian Volume Estimation and Developing HCM Pedestrian Methodologies for Safe and Sustainable Communities; ⁽¹⁶⁾ NCHRP 15-57: Highway Capacity Manual Methodologies for Corridors Involving Freeways and Surface Streets;

Evolution of HCM methodologies

Dr. Fabio Sasahara

HCM 2010 (2010)

HCM 6th Edition (2016)

HCM 7th Edition (2022)

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