Open-Graded Friction Course
Since 2005, TDOT has been placing Open-Graded Friction Course (OGFC) pavements on interstates and other select routes as a measure to reduce wet weather crashes. This special type of asphalt mixture is designed to be porous and allow for rainwater to drain towards the shoulder underneath the riding surface as opposed to the typical “dense graded” asphalts that require water to drain on top. These porous pavements can sometimes have higher costs since they require a sealer layer be placed first, but TDOT has been monitoring these projects from the beginning to verify the additional cost is worthwhile.
The first OGFC project was placed in Fall 2005 on State Route 840, now Interstate 840 in Rutherford County between Interstate 24 and State Route 266. The following year a section was paved on State Route 76, US Highway 79 in Henry County. Both sections were re-paved in 2015. To date TDOT has paved over 300 centerline miles of OGFC, mostly on Interstates due to their high posted speeds and the increased opportunity to reduce accidents during rain events. During that time period, TDOT has been observing crash data in an effort to confidently conclude the pavements do save lives. As OGFC projects reach the 3-year age mark, crash data is gathered for the 3-year period prior to construction and compared to the same length of time following construction. Of the 221 centerline miles observed thus far, wet-weather crashes reduced by 32%. These calculations do not account for traffic growth.
To date, TDOT has awarded just over 400 centerline miles of OGFC projects, approximately 1/3 of the Tennessee Interstate system. Per these recent findings and additional findings which conclude general pavement structural performance is equivalent to dense-graded pavements, TDOT is developing a policy to hopefully increase the use of OGFC in more areas where wet-weather crashed can be reduced.