High-Friction Surface Treatment (HFST) Demonstration Event Provides an Up-Close Look at an Effective Safety Countermeasure for Friction-Critical Roadway Locations

by Matt Cate, P.E.

For manual HFST installations, V-notch squeegees are used to spread the epoxy binder to a uniform depth prior to application of the calcined bauxite aggregate.

On September 9th TTAP partnered with the Tennessee Department of Transportation (TDOT) and the Federal Highway Administration (FHWA) to present the Tennessee High-Friction Surface Treatment Open House and Demonstration. The event, held on the TDOT Region 3 campus in west Nashville, provided an opportunity for nearly 50 participants representing local agencies, engineering consultants, TDOT, FHWA, and universities to learn more about the application, benefits, and costs of high-friction surface treatments (HFST). This open house and demonstration event was funded through an Accelerating Safety Activities Program (ASAP) grant. The HFST Open House and Demonstration included a live, on-site demonstration of the HFST application process, presentations on the history, development, effectiveness, and installation of HFST, and an opportunity for questions and answers with the presenters from TDOT and FHWA.

After the binder has been spread across the entire lane, the calcined bauxite aggregate is applied by hand. The binder must be covered completely with no visible wet spots at the aggregate surface.

The HFST event began with an on-site application of HFST. This demonstration highlighted the suitability of HFST for the treatment of relatively small surface areas by local maintenance crews using inexpensive tools and equipment. During this demonstration, a four-man crew from TDOT's Materials and Tests Division went through the process of mixing the two-part epoxy binder, spreading the binder on the pavement surface using a notched squeegee, and applying the calcined bauxite aggregate. At this point the HFST was left to cure and participants went back inside for the presentations.

The first presentation was made by Frank Julian with FHWA's Resource Center. Mr. Julian covered a number of HFST-related topics related to the development, use, and application of HFST. As of July 2015, 40 states had used HFST as a safety treatment on at least one horizontal curve. Tennessee is one of only four states that have used HFST on at least 100 horizontal curves, joining California, Kentucky, and Pennsylvania. Mr. Julian stressed that HFST is a safety treatment first and foremost with potential applications on horizontal curves, steep grades, and intersection approaches.

US crash data indicates that 28 percent of fatal crashes occur on curves; the overall crash rate on curves is nearly three times the rate for tangent (straight) roadway segments. More than half (54 percent) of fatal crashes on curves occur on roadways that are functionally classified as collectors or local roads. Only 13 percent of these crashes occur on Interstate highways, freeways, or expressways. In Tennessee, 1,083 of 2,983 (36 percent) total roadway fatalities occurring between 2010 and 2012 were on curves. 70 percent of these crashes occurred on rural roadways. 42 percent of these crashes were on roadways classified as local streets or collectors.

Approximately 2 hours and 45 minutes after the aggregate was applied in the morning demonstration, the epoxy has cured and the surface is swept to remove loose aggregate. This loose aggregate can be reclaimed and used for future projects or for repairs to existing treatments.

Mr. Julian also presented several case studiesfrom across the country. A project in Pennsylvania reduced total crashes from 26 in the 3 years prior to installation to one in the nearly 3 years following HFST installation in October, 2012. In Wisconsin, installation of HFST on a curve in an interstate interchange resulted in a decrease from 219 crashes in the 2 years, 10 months prior to installation to 9 crashes in the 2 years, 11 months since installation.

In California, HFST was selected as an alternative to roadway realignment in an environmentally-sensitive location. HFST was selected on the basis of savings in environmental review and project design (4-6 months versus 2-5 years), construction duration (10 days versus 6+ months), and cost ($250,000 versus $14,000,000 or more). HFST also eliminated the need for a lengthy detour since the surface treatment can be applied to one lane at a time. A similar project in South Carolina utilized HFST based on safety benefits (56.5 percent reduction in all crashes, 68.1 percent reduction in wet-weather crashes), project cost ($1 million versus $5 million), and time to implementation (6 months versus 3 or more years).

A final case study in Kentucky showed the cumulative effect of the state's HFST program. Overall, locations with HFST showed a 90 percent reduction in wet-weather crashes, a 77 percent reduction in dry-weather crashes, and an overall crash reduction of 87 percent. Broken down by location type, ramps, curves, and intersection approaches showed overall crash reductions of 95 percent, 87 percent, and 90 percent, respectively.

The second presentation of the day was made by Brian Hurst with TDOT's Project Safety Office. Mr. Hurst's presentation discussed the role of HFST in Tennessee's Strategic Highway Safety Plan (SHSP). HFST is primarily used as a countermeasure to reduce the frequency and severity of roadway departure crashes resulting from a lack of surface friction at locations including horizontal curves, steep grades, and intersection approaches. Roadway departure is involved in 63 percent of Tennessee's fatal crashes and 42 percent of crashes involving serious injury. The presentation detailed that HFST can be expected to reduce rural lane departure crashes by 35 percent and urban lane departure crashes by 54 percent. With this demonstrated effectiveness against lane departure crashes, Tennessee's SHSP identifies high-friction surface treatments as major initiative in the plan's Infrastructure Improvements emphasis area.

Mr. Hurst also discussed TDOT's use of HFST at four locations across the state, providing a comparison of before and after crash data for each location. At the first location on Interstate 24 in Marion County, the three-year period prior to HFST installation saw 7 total crashes, 4 lane departure crashes, and 1 wet-weather crash. In the three years since the installation of HFST in 2012, the site has experienced 4 crashes, 3 lane departure crashes, and no wet-weather crashes. Using similar three-year crash comparisons, the Cocke County location on Morrell Springs Road saw decreases from 10 to 4 total crashes, 7 to 3 lane departure crashes, and 4 to 1 wet-weather crashes. A Cheatham County site on State Route 249 saw decreases from 6 to 0 total crashes, 1 to 0 lane departure crashes, and 1 to 0 wet-weather crashes. Finally, a Davidson County site on Interstate 440 showed dramatic improvement from the before to the after period. In the three years prior to the installation of HFST in 2008, the site saw 31 total crashes, 31 lane-departure crashes, and 31 wet-weather crashes. In the 7 years since HFST was installed, the site has seen only 1 wet-weather lane-departure crash.

The final presentation was delivered by Danny Lane with TDOT's Research and New Product Evaluation Section. Mr. Lane provided additional information about the HFST installation on the flyover ramp rom eastbound Interstate 440 to westbound Interstate 24 in Nashville. The HFST was installed by TDOT maintenance forces on a Saturday morning in October 2008 and is still in service today. Mr. Lane and Joseph Kerstetter represent TDOT on the High Friction Surfacing Council, the group responsible for the American Association of State Highway and Transportation Officials' (AASHTO's) Standard Practice for High Friction Surface Treatment for Asphalt and Concrete Surfaces, a document which serves as the basis for TDOT's own Special Provision Regarding High Friction Surface Treatments (SP406HFST).

TDOT also participates in AASHTO's National Transportation Product Evaluation Program (NTPEP), a program designed to evaluate and approve products for use by state departments of transportation across the nation. Through NTPEP, HFST products are applied to "test decks" hosted by the Kentucky Transportation Cabinet. The products evaluated through NTPEP are reflected in TDOT's Qualified ProductsList (QPL).

Finally, Mr. Lane detailed the recent extent of TDOT's use of HFST. TDOT applied 120,000 square yards of HFST on the state's roadways in 2014. The agency's 2015 usage is expected to equal or exceed this number. Mr. Lane also discussed the use of HFST on bridge decks, where it can be used in the rehabilitation of existing structures or as a sealant to prolong the life of new structures.

Following these presentations, the group returned to the spot where the HFST installation was performed earlier in the morning. After two and a half hours the epoxy had cured to the point that the surface could be swept to remove loose aggregate. In this case the process was performed using a broom attachment mounted to the front of a dump truck.

To see pictures, videos, and handouts from the Tennessee High-Friction Surface Treatments Open House and Demonstration event, please visit the TTAP website at http://ttap.utk.edu.