The AASHTO Subcommittee on Highways issued a resolution on Flexibility in Design Standards. The current minimum Stopping Sight Distances (SSDs) in AASHTO’s A Policy for Geometric Design of Highways and Streets, 2011 (a.k.a. Green Book) are not threshold values and substantial deviations can be made without impacting crash rates or severity. The very conservative SSD criteria result in lengthy minimum sight distances, which reduce the flexibility for the design and can result in additional costs, additional use of resources, and design exceptions with no apparent safety benefit. SSD is one of the 10 Controlling Design Parameters established by FHWA and should represent a safety threshold.
The research objective is to determine a cost-effective SSD model for 2R/3R, Reconstruction, and New Construction Projects and revised text for an update of the AASHTO Green Book.