CASE STUDY

NORTHERN CALIFORNIA

US 199-Del Norte County

HIGH FRICTION SURFACE TREATMENT (HFST)

Northern California, near the Oregon State line is home to the Redwood National and State Parks, which span over 200 square miles and 

are some of the most environmentally diverse areas in the United States. Accordingly, transportation construction projects that disturb 

existing conditions within the parks’ limits are subject to stringent environmental restrictions and long permitting processes. 

A Life-Saving and Cost-Effective Solution 

for an Environmentally Sensitive Location

Figure 1. US 199 in Del Norte County

Photo: Caltrans

BACKGROUND

Over the last decade, a horizontal curve within the parks’ limits 

experienced a high frequency of wet crashes. This curve, shown 

in Figure 1, is located on US 199, a two-lane, rural highway in Del 

Norte County, approximately one mile east of the South Fork 

Road intersection. It has a radius of 280 ft. and an advisory speed 

of 30 miles per hour (mph). Between 2006 and 2009, this site 

experienced 26 wet crashes and exhibited total and severe (fatal + 

injury) crash rates that were 7.3 and 4.3 times, respectively, greater 

than the statewide average for similar facilities. Crash types 

included run off road, head-on, and opposite direction sideswipe. 

Caltrans previously installed several low-cost safety 

countermeasures at the site including center line rumble strips, 

speed warning signs, double stacked chevron signs, and one inch 

open grade asphalt concrete (OGAC) overlay. Yet, these treatments 

did not lead to the crash reductions Caltrans desired. They began 

to consider larger scale countermeasures, specifically roadway 

realignment. However, the realignment process would require a 

lengthy environmental review and mitigation of wetland impacts 

before the improvement could begin reducing crashes. As an 

alternative to realigning this curve, Caltrans began to investigate a 

High Friction Surface Treatment (HFST) and looked to other States 

for guidance and successes.

FACTORS EFFECTING THE FINAL DECISION

Most critical for Caltrans at this location 

was mitigating environmental impacts. 

US 199 parallels the Smith River, the most 

pristine and environmentally sensitive river 

in California, protected by a full spectrum 

of environmental entities and regulations. 

The surrounding area sustains California’s 

most diverse ecology, including the Marbled 

Murrelet and Northern Spotted Owl, as 

shown in Figure 2, both threatened species 

protected by the Federal Endangered 

Species Act. The area also contains over 400

separate species of plant life and a large 

number of active, very small wet lands. 

Due to endangered species and water quality 

concerns, a roadway realignment project within the parks’ limits 

would require Caltrans to spend six months acquiring environmental 

permits. Further, the North Coast Regional Water Quality Control 

Board requires Caltrans to mitigate construction effects upon the 

wetlands, even when impacts are only a few square feet. Wetland 

and impervious area mitigation ratios can range from 1:1 to 1:4 

depending on several factors. If the replacement is to take place 

within another roadway project, it could be years before Caltrans 

is able to begin work on the initial project as crashes continue to 

NPS Photo

Figure 2. Threatened Species

Northern Spotted Owl

NPS Photo

NPS Photo

Marbled Murrelet
 NORTHERN CALIFORNIA

HIGH FRICTION SURFACE TREATMENT (HFST)

occur. In contrast, HFST environmental impact and associated 

review is minimal and requires only a Categorical Exemption/

Exclusion (CE/CE) document. HFST’s nominal effect on the 

surrounding environment is due to the treatment’s application 

between existing pavement edges, resulting in no net increase 

of impervious areas within the Park’s limits.

In addition, any geometric improvement that involves 

construction incurs time restrictions (i.e., environmental 

windows) aimed at not disturbing wildlife. This would force 

Caltrans to either perform large-scale construction projects 

in stages or to use an accelerated/restricted schedule, both of 

which have significant effects upon the project. Conversely, HFST 

has the distinct advantage of an installation time period of just 

10 working days.

Lastly, a feasible detour route for the realignment is not available 

because a network of local county roads that connects the lower 

and upper portions of the county does not exist. A detour around 

US 199 could take longer than 8 hours, which is estimated to cost 

upwards of $450 million a year in associated economic losses. 

HFST can be installed one lane at a time and therefore does not 

require a detour at any point during construction.

Figure 3. US 199 HFST Application Area

Photo: Caltrans

10 Working Days

HFST

Curve 

Realignment

Environmental Review 

& Design Timeframe

Cost

Detour

Construction Duration

4-6 Months

~$250,000

6+ Months

2-5 Years

$14,000,000+

Table 1 summarizes and compares each countermeasure’s environmental review and design time frames, construction duration, costs, 

and need for a detour.

SELECTING HFST

In summer 2012, Caltrans opted for the simpler, but still very effective, 

alternative. They installed 850 ft. of HFST at this horizontal curve on 

US 199, shown in Figure 3. The treatment consisted of a double layer 

of epoxy-resin binder with calcined bauxite aggregate, which filled 

in the surface voids from the previously installed OGAC and added 

protection against water penetration. With a peak hour volume of 

approximately 600 vehicles per hour (vph), Caltrans estimated only 

a 5 minute travel time delay during active construction. Caltrans is 

unaware of any crashes at this location since the HFST implementation.

To date, 139 sites on State maintained roadways in California have 

received HFST or will receive the treatment in the near future. Caltrans 

continually encourages and tries to educate its districts about the 

benefits of HFST. The agency believes that HFST is one of the best 

tools in its toolkit for challenging curves and should be the primary 

“go-to” friction enhancing countermeasure, even before OGAC.

Table 1. Comparison of Factors between HFST and Curve Realignment on US 199

Necessary: Roadway must be 

closed during construction.

Not Necessary: Treatment can 

be installed one lane at a time.

Frank Julian

FHWA Resource Center

frank.julian@dot.gov

Joseph Cheung

FHWA Office of Safety

joseph.cheung@dot.gov

FOR MORE INFORMATION

FHWA-SA-15-055

http://safety.fhwa.dot.gov

HFST could be implemented quickly 

compared to alternatives, satisfying Caltrans’ 

environmental concern, construction time 

schedule, and window of opportunity.

END HFST

BEGIN HFST

HIGH FRICTION SURFACE 

TREATMENT (2 Applications)

Grind/AC Fill (Rumble Strip)

PM 8.32

PM 8.24

Staging

Staging

What criteria does Caltrans use to install HFST?

Caltrans believes HFST is an appropriate safety countermeasure for both wet and dry locations, high and low volume 

roadways, and tangents as well as curves. It is effective at mitigating crashes involving large changes in speeds 

(acceleration/deceleration), low skid numbers, tight horizontal curves, and roadway departure. As a result, Caltrans 

has implemented HFST on a large variety of locations including horizontal curves, bridges, wet crash locations, 

signalized intersections, on- and off-ramps, and short freeway segments.

Are there any locations where HFST is not appropriate?

Caltrans does not apply HFST in cold/icy locations where heavy trucks frequently use chains in winter, as the chains 

significantly decrease HFST’s lifespan. Further, in long tangent sections with intense rainfall, OGAC is preferred.