The National Academies

NCHRP 03-107 [Completed]

Work Zone Capacity Methods for the Highway Capacity Manual

  Project Data
Funds: $600,000
Research Agency: Kittelson & Associates
Principal Investigator: James Schoen
Effective Date: 5/17/2012
Completion Date: 4/16/2015

The objective of this research was to develop improved material on the capacity of work zones suitable for incorporation into the Highway Capacity Manual (HCM). The material should (1) define work zone capacity, (2) describe procedures for field measurement of work zone capacity, (3) present analytical techniques or methods to estimate the capacity of work zones, (4) provide recommendations for the calibration of work zone capacity in microscopic simulation models, and (5) include example problems. Although consideration of diverting traffic is important in analyzing maintenance of traffic alternatives, it is beyond the scope of this project.


The revised final report has been received from the contractor and is expected to be published as an NCHRP Web-Only Document.  The results of this project are on schedule to be incorporated into the Major Update of the Highway Capacity Manual being carried out under NCHRP 03-115.

Work zone mobility is a major concern for transportation agencies due to maintenance and construction needs and increasing traffic congestion. Nearly 24 percent of non-recurring congestion is caused by work zones and recent federal rules require systematic impact assessment during the planning, design, and construction of projects, as well as development of Transportation Management Plans for all federal-aid highway projects.

The emphasis on work zone impact assessment, which includes analysis of maintenance of traffic (MOT) alternatives, mitigation strategies, and road-user costs, has resulted in the rapid increase in development and use of related analytical methodologies, modeling, and tools. These analytical tools are used by transportation agencies to make multi-million dollar MOT decisions, determine work hours and project scheduling, and develop incentives/disincentives and lane rental fees. Selection of suboptimal MOT alternatives and other impact mitigation strategies may result in increased congestion, degraded travel time reliability, and increased rear-end crashes due to queues.

A good understanding of work zone capacity is important for the proper use of spreadsheet/sketch-planning tools as well as simulation tools. The Highway Capacity Manual (HCM), the fundamental reference document for determining roadway capacity and level of service, has limited information on freeway work zone capacity, and additional information is needed to address the range of work zones for the various facility types and conditions. Guidance is also needed on how to calibrate microscopic simulation models to accurately account for work zone capacities.

Task 1. Prepare a comprehensive literature review on work zone capacity that (a) summarizes and critically evaluates significant work zone capacity studies, (b) presents working definitions for work zone capacity for the various facility types in the HCM and for different traffic conditions and contexts, (c) documents procedures commonly used to measure capacity in the field, (d) identifies critical factors that impact work zone capacity, and (e) lists and describes available data sources that could be useful in this effort.

Task 2.
Describe and evaluate modeling approaches that have been used to compute work zone capacities for freeways, multi-lane highways, two-lane roads, and arterial streets in urban and rural settings. Identify promising modeling approaches for the different facility types.

Task 3.
Develop analytical frameworks for estimating work zone capacities for all facility types included in the HCM. The frameworks should address typical work zone configurations and other critical factors. Describe data gaps and inconsistencies in past studies that would need to be addressed to develop the frameworks into analytical methods suitable for inclusion in the HCM.

Task 4.
Develop a geographically diverse data collection plan to address the critical data gaps and inconsistencies identified in Task 3. The data collection plan should include provisions for validating the methodologies that will be developed.

Task 5.
Submit an interim report summarizing the results of Tasks 1 through 4 and presenting an updated work plan for the remaining tasks. Meet with the NCHRP project oversight panel for the review and approval of the interim report.

Task 6.
Execute the data collection plan as identified in Task 4 and approved or modified at the interim meeting.

Task 7.
Develop capacity estimation models or guidance to support the analytical frameworks as approved by the panel. The models and guidance should account for factors such as facility types and setting, work zone configurations, traffic control, duration of work zone, work zone activities, traffic composition and characteristics, and other critical influencing factors within the work zone environment. Development of the models should consider any differences found between queue discharge flow and pre-breakdown maximum throughput.

Task 8.
Recommend approaches for the selection and adjustment of appropriate parameters to accurately reflect work zone capacity in microscopic simulation models commonly used for work zone analysis. Insofar as practical, the approaches should be independent of the model used.

Task 9.
Develop material suitable for inclusion in the HCM comprising the results of Tasks 7 and 8. The material should be consistent with the format of the HCM 2010, including use of exhibits, worksheets, and example problems. Recommended changes to existing text should be highlighted.

Task 10.
Submit a final report that documents the entire research effort and includes the Task 9 material as a stand-alone appendix. In addition, provide a PowerPoint presentation describing the research effort and the principal recommendations for the HCM.

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