The National Academies

NCHRP 20-07/Task 075 [Completed]

Geometric and Roadside Safety for Very Low Volume Roads
[ NCHRP 20-07 (Research for AASHTO Standing Committee on Highways) ]

  Project Data
Funds: 75000
Research Agency: CH2M Hill
Effective Date: 2/1/1996
Completion Date: 8/31/1998
Comments: Completed

Task 75, FY 1997, "Design Guidelines for Low Volume Roads" (Mr. Timothy R. Neuman, CH2M Hill). The current AASHTO Policy on Geometric Design for Highways and Streets, (Green Book) established minimum geometrics (widths, vertical alignments, cross sections and safety [clear zone]) for new construction and major reconstruction of various road classifications, traffic volumes, and design speeds. These minimum criteria for roadway widths were based on recent research contained in NCHRP Report 362: Roadway Widths for Low-Traffic-Volume Roads. TRB Special Report 214: Designing Safer Roads: Practices for Resurfacing, Restoration, and Rehabilitation. As noted in NCHRP Report 362, 90% of rural two- lane roads carry less than 1000 vehicles per day and 80% carry less than 400. The requirements of meeting the Green Book geometrics and clear zone are causing considerable funds to be expended on relatively few miles of roads while many miles need to be updated. Improvements to roads with 0-400 vehicles per day to meet the Green Book criteria may not be a cost-effective approach to achieve overall operational and safety improvements on a systemwide basis. The objective of this project is to develop design guidelines for very low-volume roads suitable for insertion into Chapter 5 of the Green Book. These guidelines will be submitted to the Geometric Design Task Force of the AASHTO Subcommittee on Design for their consideration. The final report has been submitted to AASHTO for disposition and is also available here.

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