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Roadway Departure | August 2022
“Anytime you can reduce crashes by nearly 80% without moving dirt, everybody wins.”
- Andy Vandel
Highway Safety Engineer - SDDOT
From 2013 through 2017, South Dakota experienced an average of 3,479 fatal and serious injury crashes with 59% of these crashes being lane departure crashes. Through investigation of their lane departure crashes, the South Dakota Department of Transportation (SDDOT) identified lane departure crashes were five times more likely to involve winter road conditions than wet road conditions. Furthermore, a third of the lane departure crashes occurred on horizontal curves, even though horizontal curves account for less than 10% of the system.1
In 2014, SDDOT installed high friction surface treatments (HFST) at four horizontal curves with crash rates two to four times higher than the statewide average. Most of these incidents occurred during winter road conditions. SDDOT used calcined bauxite with AASHTO Standardized Specifications. SDDOT also identified four criteria to use when assessing appropriateness of HFST for a curve:
A simple before-after analysis was conducted at these four locations, which showed a 78% reduction in roadway departure crashes in 2015 when compared to the average number of crashes per year for the before period of 2009 through 2013. Similarly, SDDOT observed an 89% reduction for 2016 compared to the before period crashes. Based on this experience, SDDOT expanded the use of HFST. In 2017, SDDOT installed HFST at 15 locations with a high frequency of winter-road-condition crashes. After two winters, a simple before-after analysis of the crash data showed a 78% reduction in total crashes, and an economic analysis revealed a benefit-cost ratio of 12:1 from these projects. SDDOT estimates the use of HFST in South Dakota will save $18 million in societal crash costs.
Due to the success of these projects, now SDDOT has biennial HFST treatment projects in their State Transportation Improvement Program (STIP), and HFST is currently in use at 48 locations. HFST is a proven safety countermeasure suitable for all weather applications at strategic locations. Other State DOTs, even States that experience severe winter conditions, should not be reluctant to install a HFST as a safety countermeasure to reduce lane departure crashes at strategic locations, especially locations involving winter road condition. SDDOT has not experienced durability issues associated with HFST due to snow removal.
Noteworthy Practice for South Dakota HFST for Winter Road Conditions
FHWA Office of Safety’s website: High Friction Surface Treatments
How FHWA is addressing roadway departure and pavement friction:
Enhancing Safety through Continuous Pavement Friction Measurement
RSPCB Program Point of Contact
Felix Delgado, FHWA Office of Safety
Felix.Delgado@dot.gov
FHWA Office of Safety
Staff and Primary Work Responsibilities
FHWA Office of Safety
Safety and Design Team
FHWA Resource Center
