Recommendations Report for

High Friction Surface Treatments

Candidate Sites, Materials, and Construction

FHWA Safety Program

http://safety.fhwa.dot.gov
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Cover photos coutesy of: Left-FDOT (1); Upper right-FDOT (1), Lower right-TTI
Technical Report Documentation Page

1. Report No.

FHWA-SA-20-036

2. Government Accession No. 3. Recipient’s Catalog No.

4. Title and Subtitle

Recommendations Report for High Friction Surface Treatments: Candidate Sites, 

Materials, and Construction

5. Report Date

July 2020

6. Performing Organization Code 

7. Author(s)

Bryan T. Wilson, Kelvin C. P. Wang, Joshua Q. Li, Guangwei Yang

8. Performing Organization Report No.

9. Performing Organization Name and Address

Texas A&M Transportation Institute

1111 RELLIS Parkway 

Bryan, TX 77807

Oklahoma State University (OSU)

207 Engineering South

Stillwater OK 74078

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH6116D00004/0003

12. Sponsoring Agency Name and Address

Federal Highway Administration – Office of Safety

US Department of Transportation

1200 New Jersey Avenue, SE

Washington, DC 20590

13. Type of Report and Period Covered

Informational Report

14. Sponsoring Agency Code

FHWA-HSA

15. Supplementary Notes

Joseph Cheung, Technical Manager, Office of Safety, FHWA

16. Abstract

High friction surface treatment (HFST) is a safety-first pavement treatment intended to restore and maintain pavement friction to 

reduce crashes. The cost of HFST is high compared to typical maintenance treatments; however, HFST is highly effective at 

reducing wet-weather and run-off road crashes. Improvement in the state of the practice can promote more widespread deployment 

resulting in more crash reductions and a longer lasting safety countermeasure. This document provides recommendations on the 

identification of candidate sites, materials selection, and proper construction practices. Much of this guidance is derived from two 

documents: “High Friction Surface Treatment Curve Selection and Installation Guide,” by Atkinson et. al. in 2016, funded by FHWA; 

and “High-Friction Surface Treatment Guidelines: Project Selection, Materials, and Construction” by Wilson and Holzschuher in 

2016, funded by FDOT and FHWA. Relevant recommendations from the recently completed Long-Term Performance Monitoring 

Study were also incorporated into this document.

17. Key Words

High Friction Surface Treatment (HFST), Recommendations, Candidate, 

Materials, Construction

18. Distribution Statement

No restrictions. 

1

OVERVIEW

High friction surface treatment (HFST) is a safetyfirst pavement treatment intended to restore and 

maintain pavement friction to reduce crashes

(FIGURE 1). It is a thin layer of high-quality polishresistant aggregate bonded to the pavement surface 

with a polymer resin binder.

Photo courtesy of FDOT (2)

FIGURE 1 – High Friction Surface Treatment.

The cost of HFST is high compared to typical 

maintenance projects (unit cost is typically around 

$25 to $35/sy). Hence, there is incentive to improve 

the state of the practice to promote more 

widespread deployment resulting in more crash 

reductions and to provide a longer lasting safety 

countermeasure.

The purpose of this document is to provide 

recommendations on the identification of: 

1) candidate sites,

2) proper materials selection, and 

3) construction practices.

Many of the recommendations are derived from 

two documents: “High Friction Surface Treatment 

Curve Selection and Installation Guide,” by Atkinson 

et. al. in 2016, funded by FHWA (3); and “HighFriction Surface Treatment Guidelines: Project

Selection, Materials, and Construction” by Wilson 

and Holzschuher in 2016, funded by FDOT and FHWA

(2). The relevant recommendations from the 

recently completed Long-Term Performance 

Monitoring Study are also incorporated into this 

document. 

CANDIDATE SITES

What to Look for and Avoid

HFST is, first and foremost, a safety treatment 

used specifically to reduce run-off-the-road and 

other wet-weather crashes. Crash reduction has 

proven most effective on rural and urban horizontal 

curves and tight-radius loop ramps. HFST has also 

been applied at high-volume intersections and 

downhill approaches where stopping sight distance 

is limited, though the measured safety benefit in 

these scenarios is still being studied. Other scenarios 

include approaches to rail crossings, school 

crossings, and tolling areas, though safety 

performance data was not available for these 

locations.

The safety-related site criteria that agencies use 

to assess the appropriateness of an HFST application 

are locations with:

• High crash frequency.

• Low pavement friction.

• Large speed differential and geometric factors.

• Failure of previously installed lower-cost 

treatments.

From a materials longevity perspective, agencies also 

consider:

• Existing pavement condition.

Each of these topics are discussed in this section 

followed by a guidance summary on where and 

where not to apply HFST in TABLE 1.

High Crash Frequency

The first criterion is a history of high crash 

frequency. Various network screening methods are 

outlined in Chapter 4 of the AASHTO Highway Safety 

Manual (HSM). The HSM provides a network 

screening process to identify and rank sites on their 

potential for reducing crash frequency and/or 

severity. There are five steps in the process: establish 

the focus of network screening, identify the network 

and reference population, select the performance 

measures, select screening method, and screen and 

Most effective on rural and urban horizontal 

curves and loop ramps.
2 RECOMMENDATIONS REPORT FOR HIGH FRICTION SURFACE TREATMENTS

evaluate the results. The network screening process 

as outlined in the HSM is very applicable to 

identifying sites with the potential for crash 

reduction with HFST treatment. 

The most straight-forward approach is obtaining 

the total reported crashes per year at a given 

location or calculating the average crash rate over a 

number of years (average crash frequency). A more 

robust method, described in the HSM, is used to 

estimate expected average crash frequency by using 

a combination of observed crashes and predicted 

crashes from carefully calibrated safety performance 

functions. 

Agencies may focus on specific crash types when 

identifying candidate sites. Wet-weather crashes, for

example, are more indicative of a friction deficiency 

than total crashes. Agencies may even normalize the 

wet-weather crash frequency by the percent wettime, which would highlight how much the wetweather crashes might be overrepresented in that 

location. Focusing on run-off-road crashes is also 

recommended. For example, in 2009, the Kentucky 

Transportation Cabinet identified over 150 sites with 

high frequency of crashes, then selected the 30 sites 

with the highest run-off-road crash rates with a 

wet/dry crash ratio greater than 50 percent (4).

Another consideration is for the crash severity. A 

property-damage-only crash has a much smaller 

impact socially and economically than an injury or 

fatality crash. Agencies may prioritize sites with 

higher crash severities over other sites to maximize 

their safety investment. FHWA developed a guide 

entitled “Crash Costs for Highway Safety Analysis”, 

which proposed national-level crash costs, as well as 

provided procedures and a spreadsheet tool to assist 

states in calculating state-specific values, and update 

costs over time. The guide and supplemental 

spreadsheet are available here:

https://safety.fhwa.dot.gov/hsip/planning.cfm

Low Pavement Friction

Wet-weather crashes are largely related to 

friction deficiencies on the pavement. A study by 

Pratt et. al. with the Texas A&M Transportation 

Institute developed crash modification factors that 

include the effect of skid resistance (5). The authors 

found a significant increase in crashes as the skid 

number (SN50S) decreased (FIGURE 2). On average, 

wet-weather run-off-road crashes doubled as the 

skid number dropped from 40 to 20, and crashes 

were halved as the skid number increased from 40 to 

80. 

Graph courtesy of TxDOT (5)

FIGURE 2 – Skid Number Crash Modification Factors 

for Wet-Weather Crashes.

State agencies with pavement management 

systems routinely measure the skid number along 

the roadway network. The skid numbers are often 

incorporated into decision-making tools for 

maintenance funds allocation. Skid number, 

however, is not collected along horizontal curves in 

most agencies due to the inability of traditional 

friction measurement devices to operate on 

horizontal curves without traffic interruption. 

Instead, skid number is measured at tangent sections 

ahead of the curve to infer the skid number along the 

curve section. After a candidate site is identified 

based on crash frequency, most agencies then 

collect friction data specifically on the curve. If 

interested in routinely testing skid on horizontal 

curves, an agency could use a continuous friction 

measurement device like a Side-Force Coefficient 

Routine Investigation Machine (SCRIM) or a Grip 

Tester. A macrotexture measurement is also 

important for assessing wet-weather safety.

When the high-crash site skid resistance is substandard, the agency decision-makers should

explore pavement treatment options to restore or 

enhance the site friction and reduce the crash rate. 

Amongst all the pavement treatment solutions, HFST 

is well-suited when the existing skid numbers are 

typical for the area but still insufficient to meet the 

friction demand, or when the agency is concerned 

traditional materials will not adequately maintain 

good skid performance due to high friction demand.
3

Large Speed Differential and 

Geometric Factors

The speed differential in a horizontal curve is 

defined as the difference between the posted speed 

limit for the tangential roadway segment and the 

advisory speed for the curve. The greater the 

differential, the faster a driver needs to decelerate to 

safely maneuver through the curve without losing 

control, and the greater the friction demand will be. 

Herrstedt and Greibe, from Denmark, evaluated 

curve risk based on the energy required to change a 

vehicles speed going into a curve (6). They defined 

curve risk categories based on the 85th percentile 

tangent speed and the curve design speed (FIGURE 

3). HFST can provide additional friction to the 

motorist when rapid deceleration is required, such as 

in categories D and E.

Graph courtesy of Traffic Engineering and Control (6)

FIGURE 3 – Curve Risk Categories.

The curve radius is a significant factor in setting 

curve advisory speeds. Pratt et al. related a small 

curve radius with an increase in crash frequency (5). 

The crash rate increases exponentially as curve 

radius decreases (FIGURE 4). In the same study, Pratt 

et al. developed the Texas Curve Margin of Safety 

spreadsheet program. The Texas Department of 

Transportation uses this program to compare the 

friction margin of safety at three key points along a 

curve’s length, which illustrates how the greatest 

friction enhancement is needed at the beginning and 

mid-points of the curve.

Graph courtesy of TxDOT (5)

FIGURE 4 – Crash Modification Factor as a Function 

of Curve Radius.

By focusing on wet-weather and run-off-road 

crashes, the agency will naturally filter down to tightradius horizontal curves and loop-ramps (FIGURE 5). 

Sites might also include high-approach speed 

intersections, and sensitive locations with high 

pedestrian volumes like in-front of public schools.

Photo courtesy of FDOT (1)

FIGURE 5 – HFST on Tight Curve Before Intersection.

Failure of Prior Low-Cost 

Treatments

Outside of a geometric redesign, HFST is a

comparatively expensive treatment for crash 

reduction. Agencies often employ different low-cost 

treatments first, such as:

• Horizontal alignment signs (see MUTCD).

• Center line and edge line pavement markings.

• On-pavement or vertical roadside delineators.

• Advanced curve warning pavement markings.

• Audible milled-in rumble strips.

• Guardrail.
4 RECOMMENDATIONS REPORT FOR HIGH FRICTION SURFACE TREATMENTS

Signs, markings, and rumble strips require the driver 

to first observe and then react to avoid a crash. A 

guardrail does not prevent crashes but mitigates the 

crash severity. HFST, on the other hand, is a passive 

countermeasure that is always acting to help the 

driver stay on the road as they navigate a curve. If 

the other countermeasures fail to reduce crashes to 

an acceptable level, HFST may be the next most costeffective option.

Existing Pavement Condition and 

Maintenance

HFST should only be used on structurally sound 

pavements requiring minimal surface repair. If the 

pavement surface is in marginal or poor condition, or 

has any significant non-structural defects, the agency 

should repair or replace the layer. HFST applications 

on weak and aged pavement can actually accelerate 

pavement failure. For asphalt pavement, mill out the 

deteriorated layer and replace it with an asphalt 

inlay. For concrete pavement, repair or replace 

distressed slabs. The types of surface defects that 

would require surface repair/replacement include:

ASPHALT PAVEMENT

• Moderate-severity cracking.

• Rutting greater than 0.25 inches.

• Raveling.

• Flushed sealcoat.

CONCRETE PAVEMENT

• Moderate or severe:

o Transverse cracking.

o Longitudinal cracking.

o Spalling.

o Corner cracking.

• Shattered slab in more than three pieces.

The agency must still ensure that the surface 

distress is not related to larger structural problems

through a forensics investigation. A pavement 

engineer could:

• Review the as-built pavement design.

• Collect field cores to assess:

o Cracking patterns.

o Debonding.

o Deeper layer deterioration.

• Measure deflections with non-destructive 

falling-weight equipment.

If there is a structural problem, the pavement would 

require extensive rehabilitation, at which time 

realigning the curve or correcting the superelevation 

may be more cost effective to improve safety.

HFST applications over open-graded pavement 

present unique challenges which may discourage 

this approach. Because of the high voids content, 

open-graded asphalt pavement requiressignificantly 

more resin binder and often a two-layer application. 

This thick application may increase problems with 

thermal incompatibility between the HFST and the 

asphalt. Moisture may also get trapped under the 

HFST, causing stripping and substrate failure. Due to 

several premature failures, the Florida Department 

of Transportation does not allow placement directly 

on open-graded friction course (1). In Florida, 

existing open-graded layers need to be milled and 

inlaid with dense-graded asphalt before applying 

HFST. Other agencies may consider a similar 

approach. In contrast, applications over opengraded pavement in California have generally been 

successful (7). 

Thin polymer overlays are a common concrete 

bridge deck preservation treatment. The materials 

and application of this treatment and HFST are very 

similar, except that HFST must have high-friction 

calcined bauxite aggregate and may warrant slightly 

different resin binder properties. Therefore, the 

agency may consider applying an HFST treatment in 

lieu of a traditional thin polymer overlay for bridge 

deck treatment if safety is a major concern.

Other important maintenance operations could 

govern the use of HFST. Agency decision-makers 

should communicate with the maintenance office to 

May be placed over dense-graded asphalt 

pavement and rigid pavement. Applications 

on open-graded pavement present unique 

challenges. Agencies may opt to mill and 

inlay with dense-graded asphalt before 

applying HFST. 
5

coordinate the timing of other resurfacing 

operations around the candidate site. An agency may 

delay HFST construction if the road is scheduled for 

a mill and inlay, or the maintenance operation could 

be expedited.

Based on interviews with northern region states, 

snow removal operations through ploughing and 

deicing have no effect on HFST performance.

TABLE 1 – General Recommendations on Candidate Pavements.

Scenario Where to Use HFST Where NOT to Use HFST

Roadway

Applications

• Locations with a high crash rate related 

to a friction deficiency. 

(i.e. Run-off-the-road crashes, and 

wet-weather crashes)

• On rural horizontal curves where drivers 

tend to drive too fast for the road 

conditions and super elevations are 

inadequate.

• On tight-radius freeway loop ramps.

• At a downgrade signalized or stop 

controlled intersection approaches.

• On roadways that may need geometric 

corrections to meet the friction demand,

but the agency lacks the funding.

• On concrete pavements and bridge decks

where both preservation and safety are a 

concern.

• If less-expensive traffic control devices 

(chevrons, curve-warning signs, etc.) are 

expected to adequately reduce crashes.

• Tangent sections where crashes are 

related to driver errors.

• Following the curve beyond the PT or 

more than 1,000 ft before a curve. (No 

benefit here.)

• As a preventative maintenance 

treatment on asphalt pavement.

Pavement 

Condition

• Dense-graded asphalt or concrete.

• Pavement condition rating of “Good” and 

higher.

• Polished surface.

• Few low-severity cracks. Very few cracks 

greater than 0.25 inch Wide.

• Minor rutting ≤ 0.25 inch.

• No structural damage.

• Caution against open-graded asphalt 

without previous experience or 

appropriate pre-construction measures.

• Asphalt pavements with 6+ percent of 

cracking in or outside the wheel paths.

• Widespread rutting > 0.25 inch deep.

• Raveling surface.

• Bleeding pavement.

• Areas where layer debonding or 

subsurface stripping is suspected. (Verify 

with coring and other pavement 

forensics.)

• Concrete single slab with moderate or 

severe distress, patching, or shattered in 

more than 3 pieces.
6 RECOMMENDATIONS REPORT FOR HIGH FRICTION SURFACE TREATMENTS

Site Verification

In addition to the factors mentioned above, once 

candidate sites have been identified, the agency 

should do a thorough, in-person, review of the site 

conditions to verify that the site is still a suitable 

candidate for HFST. Much of the following check list 

was recommended by Atkinson et. al. (3):

Physically Locate Crashes.

Record Roadway and Traffic Conditions.

o Presence of skid marks.

o Damaged roadside barriers and other objects.

o Presence and condition of previous low-cost

countermeasures.

o Superelevation if applicable.

o Driver speed and general behavior.

o Speed advisory measurements.

o Point of curvature and point of tangent.

o Horizontal and vertical sight distances.

o Intersections near or within the curve.

o Heavy vehicle use (winter chains).

o Speed differentials.

Determine HFST Start and End Points.

o Start at or before where vehicles start to

brake (observe brake lights).

o Additional guidance suggested by Brimley

and Carlson with Texas A&M Transportation

Institute (8). The recommended starting point

for HFST is based on the curve speed

differential. (See Table 5.)

Conduct a Friction Test.

Check Pavement Condition.

Screening Sample Questions.

o Are the collisions related to physical

conditions of the location?

o Are existing signs, delineation, and pavement

markings accomplishing their purpose?

o Are there any specific traffic movements to

be prohibited or favored?

o Is special nighttime enhancement needed

(i.e. lighting, delineation, and sign visibility)?

o Are selective enforcement or maintenance

procedures needed?

o Is parking contributing to collisions?

o Are there adequate advance guide signs so

that motorists may choose proper lanes and

directions well in advance of need?

MATERIALS

Quality Counts

HFST is composed of hard, polish and abrasionresistance aggregate bonded to the pavement using 

a polymer resin binder. These components are 

detailed in this section.

High-Friction Aggregate

FHWA considers calcined bauxite as the 

aggregate of choice for use in HFST applications. 

Other aggregates like flint, basalt, and granite may 

only be used for preventative maintenance 

applications that are not safety-critical.

The aggregate gradation is a very fine gravel

(FIGURE 6). The maximum size is 3 to 4 mm and the 

minimum size is about 1 mm (95% passing No. 6 

sieve and 5% passing No. 16). If a larger gradation 

were used, the HFST would require more resin 

binder without any added safety benefits. 

Photo courtesy of FDOT (1)

FIGURE 6 – Calcined Bauxite Crushed & Graded.

The critical aggregate properties are a low 

aggregate abrasion value (20% max) and a high 

aluminum oxide (Al2O3) content (usually 87% 

minimum). 

In storage and transportation, the aggregates 

MUST be stay clean and dry. Any moisture in the 

aggregate could result in a poor bond and eventual 

aggregate loss.

Calcined bauxite is the aggregate of choice.
7

Where does calcined bauxite come from?

Calcined bauxite is an imported product in the 

United States, though there is one domestic source 

at the time of this report. Raw bauxite is primarily 

mined to produce aluminum. The leading bauxite 

producers are Australia, China, Brazil, India, Guinea, 

and Jamaica. When raw bauxite is heated to high 

temperatures (1,000 to 1,500°C), it undergoes 

calcination, increasing in physical hardness. Calcined 

bauxite is then crushed to size, washed, dried, and 

bagged before shipping to regional business like the 

HFST installer.

Polymer Resin Binder

The role of the resin binder system is to hold the 

high friction aggregate in place. Because traditional 

bituminous binders are soft (especially in the 

summer), they are not suitable under the extreme 

shear forces inherent to curves and approaches. A

polymer resin bindersystem with high bond strength

and other key mechanical properties is vital for the 

longevity of the HFST installation.

Polymer resin binders are multi-component 

systems that react chemically upon mixing and 

throughout the curing phase. The resin binder 

system includes a base resin, a curing agent, and 

often additives to help with meeting flexibility, 

strength, and cure time requirements. The critical 

characteristics of the resin binder for HFST 

applications are summarized in TABLE 2.

TABLE 2 – Key Characteristics of Polymer Resin Binder.

Characteristic Importance

Viscosity Spreadable without being too runny

Gel Time Adequate time to mix and apply

Cure Rate Need to open to traffic quickly

Strength Must not crush or get torn apart under traffic

Hardness Must not yield under traffic

Elongation Needs flexibility to resist cracking

Low Water Absorption Resistant to moisture-related damage

Adhesive Strength Bond to the pavement and to the aggregate

There most common HFST resin binders are:

• Epoxy-Resin - Good durability and bond 

strength. Short to long curing times, depending 

on temperature. Cannot be applied at 

temperatures below 60°F. May be susceptible to 

UV aging.

• Polyester-Resin - Good durability and bond 

strength. Short to long curing times depending 

on additive use. May be applied at lower 

temperatures. Resistant to UV aging.

• Polyurethane-Resin – Good durability and bond 

strength. Variable curing time. May be applied at 

lower temperatures. Resistant to UV aging.

Methyl methacrylate resin and other polymer 

binders are not widely accepted due to cost or 

durability concerns. The specific properties for a 

given resin binder can vary from one formulation to 

another. In time, new products are likely to emerge 

with superior properties for constructability and 

long-term performance. Also, note that some 

products produce caustic fumes or contain certain 

components that, if improperly handled, may cause 

irritation during application.

The HFST installer will likely prefer a certain

product and their installation equipment will be 

calibrated accordingly. Their equipment may be 

adaptable to different resin-binder types. 

Material Certifications

The proposed aggregate and resin binder 

materials need to be certified by the producers. The 

certifications are typically acceptable for 90 days to

12 months and whenever a new source or batch is 

used.
8 RECOMMENDATIONS REPORT FOR HIGH FRICTION SURFACE TREATMENTS

CONSTRUCTION

Tips for Success

If installed properly, HFST could last for at least 10 

years with superior skid resistance. The success of 

HFST is dependent on proper surface preparation,

mixing/application techniques, and service 

conditions. Overlooking any of these considerations 

could jeopardize the longevity of the installation.

Test Strip

It is recommended that the contractor place a 

test strip a minimum of 20-ft long before full-scale 

application. Most often this is the same day as full 

construction. The contractor will have a chance to 

identify and fix problems, and of equal importance, 

the agency inspector will become more familiar with 

the process and potential issues. If the contractor is 

prequalified and the inspector has overseen several 

successful projects, the test strip may be waived. 

Both parties should identify the following:

• Surface preparation - Adequate sweeping and 

air-washing to produce a clean, dry, dust-free 

surface. On concrete, correct shot blasting 

techniques (and subsequent cleaning) to 

produce the specified texture (FIGURE 8).

• Resin binder proportioning – Equipment 

settings to achieve the correct binder 

proportioning. Generally, the gel-time test is not 

sensitive enough to misproportioning to

substitute for proper maintenance and 

calibration of the equipment. Still, this simple 

test does have a place to ensure against major 

mixing problems. A 2-oz sample in a small paper 

cup will typically gel within 10 to 25 minutes 

(temperature dependent).

• Resin binder application rate – Equipment 

settings to achieve correct resin binder 

thickness. In production, the application rate will 

be measured by material weights and flow rates 

in the equipment. A wet film thickness gauge 

(FIGURE 7) may be helpful to verify the flow rate 

before spreading aggregate; however, the 

proper use of the gauge is very subjective on 

uneven pavement surfaces.

Photo courtesy of TTI

FIGURE 7 – Wet Film Thickness Gauge.

• Cure time – The initial cure time when traffic is 

permitted. Time will vary by product, ambient 

temperature, and surface temperature. 

Surface Preparation

Without adequate surface preparation, the HFST 

is liable to de-bonded and delaminate, especially on 

concrete. This issue is often caused by changes in 

temperature. HFST wants to expand and contract 

much more than asphalt or concrete and will pop-off 

under thermal stress if the bond is insufficient.

On asphalt pavements, first clean with a 

mechanical sweeper or vacuum sweeper, then 

follow-up with a high-pressure air wash to dry. 

Experience has shown that sweepers alone can leave 

a lot of dust on the road. Vacuum sweepers, when 

not properly maintained, can even make the dust 

situation worse. Follow these procedures for air 

washing:

• Use dry compressed air

• Use a minimum of 180 cfm

• Compressor oil traps must be functioning (or 

compressor may start misting oil!)

• Maintain air lance perpendicular and within 12 

inches of the surface.

On concrete pavement, the surface first needs to 

be shot blasted to remove curing compounds, 

loosely bonded mortar, surface carbonation, etc. 

The success of HFST is dependent on 

proper surface preparation and 

mixing/application techniques.
9

Sand blasting will be inadequate. The shot blasted 

surface should again be cleaned with a sweeper and 

a high-pressure air wash.

Don’t rush shot blasting. The rate that the shotblasting equipment moves will affect the final 

surface profile of the pavement. A fast brush-off 

blasting will not be adequate. The final surface must 

have a minimum texture of Concrete Surface Profile 

(CSP) 5 as specified by the International Concrete 

Repair Institute (ICRI). (See FIGURE 8.) The texture 

should not go beyond CSP 7. Reference CSP chips can 

be purchased online directly from the ICRI website. 

Photo courtesy of KTA-Tator, Inc (9)

FIGURE 8 – Concrete Surface Profiles.

Cover utilities, drains, and curbs to protect them 

from the HFST treatment. Tape and plastic sheeting 

work well. Pavement markings should be covered or 

removed if within the intended treatment area. Fix

any outstanding pavement distresses. Pre-treat any

joints and cracks greater than 1/4-inch wide with 

resin binder.

Applications over new asphalt pavement should 

be installed a minimum of 30 days after asphalt 

placement. In that time, any asphalt binder still 

coating the surface will likely wear away under traffic

and UV exposure. In addition, the surface texture will 

be more compact, reducing the amount of resin 

binder required for the HFST. Applications on new 

concrete pavement should also be delayed 30 days 

so the concrete can fully cure.

Equipment

Some states mandate the use of continuous 

automated or semi-automated applicator vehicles

for all projects (FIGURE 9). This automated method 

minimizes or eliminates problems often associated

with manual application methods: inadequate 

binder mixing, improper and uneven binder 

thickness, delayed aggregate placement, and 

inadequate aggregate coverage. In addition, the 

automated process is considerably faster (2,000+ 

sy/hr), permitting a quicker return to traffic.

Purely manual application methods can also 

produce treatments with adequate performance and 

durability; however, it is critical that all members of 

the crew have adequate experience with the 

process. Even when automated applications are 

mandated, manual application may still be required 

for small spot applications up to 200 sy and where 

automated equipment cannot reach.

Photo courtesy of DBi Services (10)

Photo courtesy of WSDOT (11)

FIGURE 9 – Continuous Automated and SemiAutomated HFST Applicator Vehicles.

Don’t rush shot blasting.
10 RECOMMENDATIONS REPORT FOR HIGH FRICTION SURFACE TREATMENTS

In a fully-automated method, the applicator must 

mechanically meter, mix, monitor and apply the 

resin binder and apply the aggregate in one uniform 

and continuous pass. Automated monitoring gauge 

and print-outs are typically available. This should 

help to minimize the potential for human errors. 

With some automated application systems, the resin 

binder can be heated. The heating process can help 

control the viscosity of the resin in cooler 

temperatures. In comparison, a semi-automated 

applicator will carefully mix the resin system, but 

aggregate distribution and/or binder spreading is still 

done manually.

At present, there are several HFST application 

companies that own automated and semiautomated equipment. These companies develop 

and operate their equipment in-house. New 

equipment suppliers and contractors are expected to 

enter the market as the popularity of HFST continues 

to grow. Equipment for the manual method includes:

• Containers for mixing.

• Electric mixer.

• A “Jiffy Mixer” type mixer attachment can help 

minimize air entrainment. It is best practice to 

mix each component separately prior to mixing 

them together.

• V-notched neoprene squeegees (FIGURE 10). 

Select design thatspreads resin at specified rate.

• Spiked shoes. 

• Broadcast system or blower for spreading 

aggregate (optional).

Photo by UDOT, Creative Commons BY-NC-ND licesne (12)

FIGURE 10 – V-Notched Squeegee.

Mixing

The resin binder must be proportioned correctly 

and mixed thoroughly. This is a particular problem 

when applying HFST manually. Mix for as long as the 

manufacturer recommends. Resin stored at cooler 

temperatures may require mixing for longer than 

recommended. Thoroughly work the sides and 

bottom of the container. Inadequate mixing can also 

occur with automated systems if not properly 

maintained and monitored.

Poor mixing will be very apparent as soft spots of 

uncured binder in the final HFST. These spots can be 

small (<1 sf) or substantial (several sy). Uncured HFST 

will need to be removed and replaced at the 

contractor’s expense.

Application

Applications on dense-graded HMA and rigid 

pavement require one layer of HFST. A double-layer 

HFST application may be required when placed over 

open-graded pavement. 

The resin binder should be applied to achieve a 

film thickness of 50-65 mils. The goal is to achieve 

50% embedment depth of the aggregate

(FIGURE 11). With too little binder, the risk for 

aggregate loss becomes much greater. Too much

binder, and the surface macrotexture is decreased.

Besides wasting material, too much binder can 

contribute to premature failure of the HFST triggered 

by thermal stresses at the bond interface.

The typical yield rate of the resin binder is 

between 25-32 sf/gal. Yield rates are dependent 

upon the surface texture of the pavement. Beforehand, walk the project and identify if there are any 

changes in the surface texture. Adjust the resinbinder rate whenever the surface texture changes 

significantly.

Aggregate is spread immediately following the 

resin binder. For automated systems, this should be 

in less than 10 seconds, and for manual methods 

should be done within 5 minutes. It is important that 

full embedment of the aggregate is achieved prior to 

the initial setting, or thickening, of the resin binder.

The aggregate should completely cover the binder, 

leaving no “wet” spots. The typical rate is between 

12 to 15 lbs/sq-yd. 
11

Graphic courtesy of FDOT (1)

FIGURE 11 – Aggregate Embedment.

Some agencies allow the reuse of recovered 

aggregate. When allowed, the aggregate must be 

dust-free, reused only once, and be blended with 

new aggregate. The ratio of new aggregate to 

recovered aggregate should be about 2 to 1. This will 

ensure the HFST color and texture remain uniform 

and that contaminated aggregate is not applied. The 

contractor should clearly label storage containers of 

recovered aggregate and include the project and 

date when it was fist applied.

Curing, Sweeping, and Restriping

The HFST must be allowed to cure according to 

manufacturer recommendations. The time will vary 

depending on the type of resin binder and the 

temperature. Protect the treatment from all traffic 

until cured.

After curing, excess aggregate must be removed 

by sweeping. If the contractor wants to reuse the 

aggregate, they must use a vacuum sweeper. Ensure 

that the system is clean and dry and will not 

contaminate the aggregate.

As required by the Engineer, restriping should be 

done after aggregate removal. This striping may be 

temporary or permanent, according to the contract.

HFST will continue to shed loose aggregate for 

several days and weeks. This is normal. The 

contractor must do additional follow-up sweeping 

within a specified period like 2 weeks. 

Acceptance Testing and Warranty

Agencies often have an acceptance criterion for 

friction within 30 to 90 days after installation. HFST 

requires a wear-in period under traffic before friction 

values stabilize and any premature testing will result 

in artificial results. The standards for friction testing 

are the locked-wheel skid trailer (ASTM E274) or the 

Dynamic Friction Tester (ASTM E1911) (FIGURE 12). 

Some agencies also require testing for macrotexture 

depth as this is critical for reducing wet-weather 

crashes.

Photos courtesy of TTI

FIGURE 12 – Locked-Wheel Skid Trailer (top) and 

Dynamic Friction Tester (bottom).

Some agencies have adopted 1-year and multiyear warranties as part of the bid document to 

ensure any pre-mature failures can be replaced. This 

will affect the overall bid price of the HFST 

installation. Surface defects may include:

The goal is to achieve 50% embedment 

depth of the aggregate.

50% Embedment - Good 

Too Low - Poor 

Prone to ravel 

Too High - Poor 

Low texture depth, Material waste 
12 RECOMMENDATIONS REPORT FOR HIGH FRICTION SURFACE TREATMENTS

• Delamination.

• Raveling.

• Soft spots of uncured binder.

• Excessive cracking.

The agency would define the extent of each distress 

that is unacceptable. Corrective action usually 

involves removal of the existing HFST with grinding, 

removing an area a bit larger than the distress, and 

then reapplication of the HFST.

CONCLUSION

This document synthesized the noteworthy

practices for HFST based on federal agency, state 

agency, and industry experience. By properly 

identifying candidate sites, selecting the best 

materials, and implementing high-quality 

construction practices, agencies will have the best 

return-on-investment for their HFST installations. 

Agencies can see more widespread HFST 

deployment and a longer lasting safety 

countermeasure, resulting in greater crash 

reductions.

The authors acknowledge that much of this 

information was previously reported by Atkinson et. 

al. (3) and by Wilson and Holzschuher (2). Relevant 

recommendations from the recently completed 

Long-Term Performance Monitoring Study were also 

incorporated into this document.

REFERENCES

1. Wilson, B. T., and A. K. Mukhopadhyay. Alternative 

Aggregates and Materials for High Friction Surface 

Treatments. Publication FHWA/FL-16/BDR74-977-05. 

Texas A&M Transportation Institute, College Station, 

TX, 2016, p. 159.

2. Wilson, B. T., and C. Holzschuher. High-Friction 

Surface Treatment Guidelines: Project Selection, 

Materials, and Construction. Publication FHWA/FL16/BDR74-977-05. Texas A&M Transportation 

Institute, College Station, TX, 2016.

3. Atkinson, J., J. Clark, and S. Ercisli. High Friction 

Surface Treatment Curve Selection and Installation 

Guide. Publication FHWA-SA-16-034. Leidos, Reston, 

VA, 2016.

4. Von Quintus, H., and A. Mergenmeier. Case Study: 

Kentucky Transportation Cabinet’s High Friction 

Surface Treatment and Field Installation Program. 

Publication FHWA-SA-15-038. Applied Research 

Associates, Inc, Champaign, IL, 2015, p. 32.

5. Pratt, M. P., S. T. Geedipally, B. T. Wilson, S. Das, M. 

Brewer, and D. Lord. Pavement Safety-Based 

Guidelines for Horizontal Curve Safety. Publication 

Report FHWA/TX-18-0-6932-R1. Texas A&M 

Transportation Institute, College Station, TX, 2018, p. 

174.

6. Herrstedt, L., and P. Greibe. Safer Signing and 

Marking of Horizontal Curves On Rural Roads. Traffic 

Engineering & Control, Vol. 42, No. 3, 2001.

7. Julian, F. Telephone Interview. Nov 22, 2014.

8. Brimley, B., and P. Carlson. Using High Friction 

Surface Treatments to Improve Safety at Horizontal 

Curves. Texas Transportation Institute, 2012.

9. Corbett, B. Measuring the Surface Profile of Prepared 

Concrete. KTA-TATOR, Inc. https://kta.com/ktauniversity/measuring-the-surface-profile-preparedconcrete/https://www.icri.org/. Accessed Apr. 23, 

2020.

10. Automated High Friction Surfacing Treatments | DBi 

Services. https://www.dbiservices.com/automatedhigh-friction-surfacing-treatments. Accessed Apr. 23, 

2020.

11. Anderson, K. W., M. Russell, J. S. Uhlmeyer, and J. 

Weston. Kwik Bond Polymers High Friction Surface 

Treatment. Publication WA-RD 851.1. Washington 

State Department of Transportation, Olympia, WA, 

2015, p. 46.

12. Utah Department of Transportation. High Friction 

Surface Treatment in Payson UT (30). 2012.

https://www.flickr.com/photos/utahdot/804789890

0/. Accessed Apr. 23, 2020.
13

FHWA, Office of Safety

Joseph Cheung

Joseph.Cheung@dot.gov

203-366-6994