Advisory Speed Safety Study

Karen Dixon, Oregon State University


  • Ida Schalkwyk, IvS Analytics, LLC.


This report presents a review of a research effort to evaluate the safety implications of advisory speeds at horizontal curve locations on Oregon rural two-lane highways. The primary goals of this research effort were to characterize driving operations at rural two-lane highway curve locations where advisory speed signs were present, and to determine to what extent these signs play a role in enhancing safety. Placement of advisory speed signs at horizontal curve locations in the State of Oregon is a practice aided by unique and specific state-level policies and, as such, may vary from nationally accepted procedures. Speed data was collected at 16 sites and compliance with advisory speed signs determined. An evaluation of site crash data and how advisory speed relates to historic crash information is included along with a statistical model that identifies critical variables that are associated with the posted speed and how they ultimately relate to the expected crash frequency. The research team developed a statistically based advisory speed model that assesses predicted crash outcomes based on a combination of geometric design, operations, and signage. The resulting advisory speed models were then contrasted to the expected advisory speeds based on the Oregon Policy as well as the 2009 MUTCD thresholds. They determined that the safety-based model actually predicted advisory speeds that are not as conservative as those recommended using the ballbank thresholds in the 2009 MUTCD or those identified using the thresholds Oregon has been using. Just prior to publication of this report, the Oregon Traffic Control Devices Committee (OTCDC) decided to adopt the 2009 MUTCD without making an exception to advisory speed posting guidelines. ODOT has begun to transition to the 2009 MUTCD advisory speed posting criteria. Actual adoption of the 2009 MUTCD is expected to occur in August 2011.

Project Details

Project Type:
Project Status:
End Date:
June 30,2010
UTC Grant Cycle:
OTREC 2009
UTC Funding: