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Noteworthy Practice for South Dakota

HFST for Winter Road Conditions

South Dakota High Friction Surface Treatment (HFST) Projects

In South Dakota an average of 3,479 fatal and serious injury crashes occurred from 2013 

through 2017; 59% of these crashes were lane departure crashes1. While investigating lane 

departure crashes in their state, the South Dakota Department of Transportation (SDDOT) 

found lane departure crashes were five times more likely to involve winter road conditions 

than wet road conditions. In addition, one-third of the lane departure crashes occurred on 

horizontal curves, even though horizontal curves account for less than 10% of the system2.

To help vehicles maintain their lane during critical braking and cornering maneuvers, in 2014

SDDOT installed high friction surface treatments (HFSTs) at four horizontal curves with crash 

rates two to four times higher than the statewide average, with most incidents occurring 

during snow-packed or icy road conditions3. HFST is a thin layer of calcined bauxite aggregate 

bonded to the pavement with a polymer resin binder that has long-lasting skid resistance and 

makes the pavement more resistant to wear and polishing. Since this was the first time HFSTs 

were deployed in the state, a simple before-after analysis in lieu of more advanced statistical 

analysis methods was performed at these four locations showing a 78% reduction in run-offroad (ROR) crashes for 2015 when compared to the average number of crashes per year for the before period of 2009 through 2013. 

Similarly, they observed an 89% reduction for 2016 compared to the before period crashes (see Table 1). SDDOT further observed 

that HFSTs performed well during winter road conditions.

Table 1. Crash History at Four Horizontal Curves Treated with HFSTs3

Location

Before

(2009–2013)

ROR

Total Crashes

Before

(2009–2013)

ROR Average 

Crashes/Year

After 

(Oct 2014–

April 2015)

ROR

Crashes

After

(2015)

ROR 

Total 

Crashes

After 

(2015)

% Crash 

Reduction

After 

(2016)

ROR 

Crashes

After 

(2016)

% Crash 

Reduction

I-229 NB 11 2.2 0 0 100% 1 55%

I-229 SB 18 3.6 1 1 83% 0 100%

14A Deadwood 13 2.6 1 1 62% 0 100%

14A Lead 5 0.6 0 0 100% 0 100%

Total: 47 9.0 2 2 78%* 1 89%*

* 2015 value calculated as (9.0 -2)/9.0 = 0.78 (or 78%); 2016 value calculated as (9.0-1)/9.0 = 0.89 (or 89%)

1

South Dakota Department of Transportation. 2019 South Dakota Strategic Highway Safety Plan, Pierre, SD, 2019.

2 Roadway Safety Foundation and Federal Highway Administration. 2019 National Roadway Safety Awards Noteworthy Practices 

Guide (South Dakota: Application of High-Friction Surface Treatment (HFST) in Winter Road Conditions), 

https://safety.fhwa.dot.gov/roadwaysafetyawards/2019/20200116_Noteworthy%20Guide-508%20Compliant.pdf (accessed 2021).

3

South Dakota Department of Transportation. Accelerated Innovation Deployment (AID) Demonstration Project: High Friction 

Surface Treatment, Final Report, Pierre (SD), 2015.

Figure 1: Approach to Horizontal 

Curve along I-90. Source: SDDOT
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Based on this experience, SDDOT expanded their use of HFSTs. In 2017, SDDOT installed HFSTs at 15 locations with a high frequency 

of winter-road-condition crashes (see Figures 1 and 2). 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 

use of HFSTs in South Dakota will save $18M in societal crash costs. SDDOT is pleased with the results of the HFST installations in 

reducing crashes and plans to use this treatment at additional strategic locations throughout the state2.

Identifying Treatment Locations

When assessing the appropriateness of a HFST4, agencies should consider 

curve locations with:

• High target crash frequencies (e.g., wet-weather crashes and/or 

winter-road-condition crashes above the statewide average).

• Low pavement friction.

• Large speed differentials between tangents and points of curvature 

and geometric factors (e.g., curve radius).

• Failure of previously installed lower-cost treatments.

• Structurally sound pavements requiring minimal surface repair.

Effect of Snowplows on HFST Applications

SDDOT has not encountered any challenges with the durability of HFSTs involving snow removal equipment and has not experienced 

any notable removal of HSFTs during snow removal activities. The bauxite surface wears well under heavy snowplowing5. 

Development of Standard Specifications and Methods for Application

In 2014, when SDDOT first installed HFSTs at the four locations 

determined to have an over-representation of lane departure crashes

during winter road conditions, two curves had concrete pavement and 

two curves had asphalt pavement. This allowed SDDOT to develop 

specifications for both types of pavements. The methods used to apply 

the HFSTs were very similar to how SDDOT applies an epoxy deck seal 

on a bridge deck. The only element that sets these types of 

applications apart is the type of aggregate used3.

Recently, SDDOT transitioned from a semi-automated application 

method (see Figure 3) to a fully-automated application method (see 

Figure 4). A fully-automated HFST application typically involves a 

customized truck that mechanically mixes each component of the 

binder (in accordance with the current ambient or surface 

temperature) and applies a consistent layer of the binder to the 

pavement surface followed by the placement of aggregate on the

epoxy through a drop spreader.

4 Wilson, B.T., K.C.P. Wang, J.Q. Li, and G. Wang. Recommendations Report for High Friction Surface Treatments: Candidate Sites, 

Materials, and Construction, Report No. FHWA-SA-20-036, Federal Highway Administration, Washington, DC, 2020.

5

Federal Highway Administration. High Friction Surface Treatments – Frequently Asked Questions. Report No. FHWA-CAI-14-019, 

Washington, DC., 2014.

Figure 3: Semi-Automated HFST Application Method.

Source: SDDOT

Figure 2: HFST along Horizontal 

Curve on Rural Multilane Roadway. Source: SDDOT
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One of the primary benefits of a fully-automated process is the 

time lapse between epoxy and aggregate applications is 

minimized which reduces the chance of hardening of the epoxy 

prior to placement of the aggregate. Other benefits include6:

• Even application of binder and aggregate.

• Reduced installation time, for example the range of 

application rates between manual and fully automated 

are as follows:

o Manual 200 to 1000 square yards (SY)/hr.

o Semi-automated 1800 SY/hr.

o Fully-automated 2800 SY/hr.

• Reduced exposure of workers to live traffic.

• Reduced material component waste.

Lessons Learned

Based on their experience with HFSTs, SDDOT shared several lessons learned:

• 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 HFSTs due to snow removal. HFSTs wear well under heavy snow 

plowing.

• SDDOT now applies HFSTs through a fully-automated process due to premature failures experienced on projects that used a 

semi-automated application method. 

For Additional Information

For additional information about HFSTs and their effectiveness in reducing lane departure crashes, contact Joseph Cheung, FHWA 

Office of Safety, at joseph.cheung@dot.gov. 

For additional information about SDDOT’s applications and use of HFST, contact Dustin Witt, South Dakota Department of 

Transportation, at Dustin.Witt@state.sd.us.

Publication Number FHWA-SA-21-128

6 Atkinson, J., J. Clark, and S. Ercisli. High Friction Surace Treatment Curve Selection and Installation Guide. Report No. FHWA-SA-16-

034, Federal Highway Administration, Washington, DC, 2016.

Figure 4: Fully-Automated HFST Application Method. 

Source: SDDOT