The National Academies

SHRP 2 L08 [Completed]

Incorporation of Travel Time Reliability into the Highway Capacity Manual

  Project Data
Funds: $1,500,000
Research Agency: Kittelson & Associates
Principal Investigator: Mark Vandehey
Effective Date: 2/17/2011
Completion Date: 8/31/2013

Project snapshot. More details below.

(Project Number)
Impact on Practice
Product Status

New analytical procedures have been developed and chapters on Freeway Facilities and Urban Streets have been prepared for potential incorporation of travel-time reliability in the Highway Capacity Manual (HCM). The methods are embodied in two computational engines and a final report documents the research.
The HCM is one of the most widely used transportation reference manuals in the United States and around the world. Incorporation of the L08 work into the Highway Capacity Manual will offer a new generation of analytic methods for conducting capacity and related analysis.
The final report is available at https://www.trb.org/Main/Blurbs/169594.aspx.  The proposed chapters, numbers 36 and 37, for the Transportation Research Board’s Highway Capacity Manual (HCM) are available at https://www.trb.org/Main/Blurbs/169595.aspx.  Links to download FREEVAL and STREETVAL are also on that page.

The TRB Committee on Highway Capacity and Quality of Service is discussing adoption in the HCM of the freeway and urban street methodologies. Also, four pilot projects, to be completed in mid 2014, will evaluate the L08 products under project L38

Staff Responsibility: William Hyman
The Highway Capacity Manual (HCM) historically has been among the most important reference guides used by transportation professionals seeking a systematic basis for evaluating the capacity, level of service, and performance measures for elements of the surface transportation system, particularly highways but also other modes. The HCM is useful for planning, design, preliminary engineering, and operations analysis. The HCM provides analytic concepts for characterizing traffic flow, capacity, and quality and level- of-service. It also provides guidance on analyzing facilities, segments, and points for uninterrupted flow such as freeways and multilane highways and for interrupted flow such as urban streets, signalized intersections, and two-way stop controlled intersections.
Travel time reliability is increasingly recognized as an important mobility performance measure. The HCM does not include a method to address travel time reliability, nor does it have mobility performance measures or a method to address reliability for specific types of facilities such as freeways, multilane highways and urban corridors, and segments such as freeway weaving areas.
The objective of this project was to determine how data and information on the impacts of differing causes of nonrecurrent congestion (incidents, weather, work zones, special events, etc.) in the context of highway capacity can be incorporated into the performance measure estimation procedures contained in the HCM. The methodologies contained in the HCM for predicting delay, speed, queuing, and other performance measures for alternative highway designs are not currently sensitive to traffic management techniques and other operation/design measures for reducing nonrecurrent congestion. A further objective was to develop methodologies to predict travel time reliability on selected types of facilities and within corridors.
This project developed new analytical procedures and prepared chapters about freeway facilities and urban streets for potential incorporation of travel-time reliability into the HCM. The methods are embodied in two computational engines, and a final report documents the research.
Status: The project is complete.
Product Availability: A prepublication draft of the final report, Incorporation of Travel Time Reliability into the HCM, was released in October, 2013.  It is available as an Adobe PDFProposed Chapters for Incorporating Travel Time Reliability into the Highway Capacity Manual (numbers 36 and 37) was released at the same time and is available as an Adobe PDF.  The FREEVAL and STREETVAL computational engines are also available, as well as a fact sheet.
This page was last modified on January 6, 2014.

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