The geometric design of facilities designated as low volume presents unique challenges to engineers across the United States. These roadways, designated by low traffic volumes thus reduced frequency of crashes, require the use of design principles unlike those applied to higher volume roads. Accomplishing the design of a low-volume highway – its three-dimensional features (horizontal alignment, vertical alignment and cross-section) and appurtenances to provide for drainage, traffic control and safety, requires a well-defined process. AASHTO initially developed the guidelines for geometric design of very low-volume roads in 1996 and the final product was published in 2001.
During the past 11 years, much has changed in the vehicle fleet, knowledge about driver characteristics (i.e., human factors), and safety and operations of these types of facilities. AASHTO policy requires that all reference material be reviewed and analyzed for potential updates. An assessment of the current publication and design process is needed to appropriately leverage and/or reflect recent advances and emerging issues contained in the documents.
There has been a significant amount of research in the area of low volume roadways in the past 11 years. Recent and relevant research efforts include but are not limited to:
- TRB Report on Low Volume Roads, 2011 (3 Volumes)
- NCHRP Synthesis 422, Trade-Off Considerations in Highway Geometric Design, 2011
- NCHRP Synthesis 417, Geometric Design Practices for Resurfacing, Restoration and Rehabilitation, 2011
Also, over the course of the past eleven (11) years many of the reference items called out in the Low Volume Manual have been updated with new and relevant information:
- 2004 and 2011 AASHTO “A Policy on Geometric Design of Highways and Streets”, The Green Book
- 2011 AASHTO Roadside Design Guide
- 2010 AASHTO Highway Safety Manual, 1st Edition
Current research efforts that should be considered during the course of the work include:
- NCHRP 15-34A, Performance-Based Analysis of Geometric Design of Highways and Streets
- NCHRP 15-47, Developing an Improved Highway Geometric Design Process
- NCHRP 15-48, Guidelines for Designing Low- and Intermediate-Speed Roadways that Serve All Users
- NCHRP 15-50, Guidelines for Integrating Safety and Cost-Effectiveness into Resurfacing, Restoration, and Rehabilitation Projects
- NCHRP 17-53, Evaluation of the 13 Controlling Criteria for Geometric Design
The objective of this project was to identify needed updates to current design policy, and/or necessary changes in the fundamental design process to incorporate the latest design principles.