http://safety.fhwa.dot.gov

July 2022 

FHWA High Friction 

Surface Treatments 

Frequently Asked Questions – 2022 Update

Non-Binding Contents: 

Except for the statutes and regulations cited within, the contents of this document do not have the force 

and effect of law and are not meant to bind the public in any way. This document is intended only to 

provide clarity to the public regarding existing requirements under the law or agency policies. 

Update Notice:

This High Friction Surface Treatment (HFST) Frequently Asked Questions (FAQ) 2022 replaces Frequently 

Asked Questions – High Friction Surface Treatments (HFST) – 2017 (FHWA-SA-18-004). It covers 

questions related to HFST safety, maintenance and operations, cost, environmental impacts, material 

specifications, durability, lessons learned, and installation.
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Table of Contents

GENERAL.............................................................................................................................................. 4

1. What is a High Friction Surface Treatment (HFST)?.............................................................................. 4 

2. What is the purpose of HFST?............................................................................................................... 4 

3. How are potential HFST sites identified?.............................................................................................. 5 

4. What are recommended limits for HSFT installations? ........................................................................ 5 

SAFETY................................................................................................................................................. 6

1. Are there any crash modification factors (CMFs) available for HFST? ................................................. 6 

2. What are the advantages of using HFST compared to using traditional safety treatments at 

horizontal curves?..................................................................................................................................... 7 

3. What is the safety effect of these surfaces for motorcycles and bicycles?.......................................... 8 

4. Has there been an increase in truck rollovers after installation?......................................................... 8 

5. What effect does HFST have on braking distance and stopping behavior at intersections? ............... 8 

MAINTENANCE AND OPERATIONS ....................................................................................................... 9

1. Does HFST promote higher operating speed? ...................................................................................... 9 

2. What is the effect of snowplows on this pavement treatment?.......................................................... 9 

3. Can HFST be applied in conjunction with rumble strips? ................................................................... 10

4. Does HFST accelerate tire wear? ........................................................................................................ 10

5. What maintenance is required for HFST?........................................................................................... 10

6. How is HFST removed and can it be recycled? ................................................................................... 11

COST.................................................................................................................................................. 11

1. What is the average unit cost for HFST?............................................................................................. 11

2. What is the benefit-cost ratio for HFST?............................................................................................. 11

3. How should the cost of HFST be evaluated? ...................................................................................... 12

ENVIRONMENTAL .............................................................................................................................. 12

1. What effect does HFST have on road noise? ...................................................................................... 12

2. What are some of the potential environmental benefits for HFST? .................................................. 13

MATERIAL SPECIFICATIONS / DURABILITY.......................................................................................... 14

1. What is the life expectancy of HFST?.................................................................................................. 14

2. Are these materials resistant to fuels and common de-icing agents?................................................15
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3. What is the difference between HFST and other pavement preservation treatments such as 

microsurfacing and chip seal?................................................................................................................. 15

4. Is it worth the investment to use HFST compared to other friction treatments?..............................15

5. Do these materials crack? If so, how do they resist crack erosion? ................................................... 16

6. Are there any issues with thermoplastic on HFST? ............................................................................ 16

7. What aggregates are appropriate for HFST and what sources are available? ...................................16

8. Can reclaimed aggregate be reused and are there any special requirements for disposal? .............17

9. What are some typical polished stone values (PSV) for HFST aggregates using ASTM E 303/AASHTO 

T 278 British Portable Pendulum Tester and ASTM D 3319/AASHTO T 279 British Wheel Accelerated 

Polishing Machine? ................................................................................................................................. 18

10. Several HFST aggregate durability studies were published in cooperation with FHWA and the 

National Center for Asphalt Technology (NCAT): ................................................................................... 18

11. Can HFST be placed on a bridge deck? ............................................................................................. 18

12. Are HFST systems proprietary?......................................................................................................... 19

13. Is there a certification process for contractors who want to perform this type of work or training 

resources for agency inspectors? ........................................................................................................... 19

14. Are there specifications for HFST?.................................................................................................... 19

LESSONS LEARNED............................................................................................................................. 20

1. What are the lessons learned with HFST installation? ....................................................................... 20

2. What pavement conditions caused failures that have been reported? .............................................21

3. Can patches that de-bond be fixed? ................................................................................................... 22

4. Will the polymer have a reaction with magnesium on a bridge deck? ..............................................22

INSTALLATION ................................................................................................................................... 22

1. What surface preparation and installation conditions are important for successful installation? ....22

2. Can you apply HFST over existing striping? ........................................................................................ 25

3. Is installation over an open-graded friction courses (OGFC) an issue? ..............................................25

4. What are some of the key factors that can affect the placement of HFST?.......................................27

5. What is the difference between manual and fully automated HFST installation?.............................27

6. Can agency personnel install HFST?.................................................................................................... 28

7. What are items to look for in terms of early-age performance that may indicate materials and 

workmanship issues? .............................................................................................................................. 29
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GENERAL

1. What is a High Friction Surface Treatment (HFST)? 

Definition

• HFST is a cost-effective safety and pavement surface treatment consisting of a polymeric resin 

binder and surface-applied manufactured aggregate used to increase the long-term friction 

characteristics of a pavement surface. 

Description

• HFST is a unique low-cost safety countermeasure because it is specifically intended to 

dramatically increase pavement friction for the purpose of reducing crashes associated with 

friction demand issues. There are no other known pavement surface treatments that enhance 

pavement friction to the same level while sustaining this friction enhancement over time.

• HFST is installed by spreading a thin layer (< 2 mm) of polymeric resin binder (typically epoxy or 

polyester) over the pavement surface, then broadcasting or dropping a 1- to 3-mm abrasion and 

polish-resistant manufactured aggregate (calcined bauxite) onto the resin layer. The resin binder 

bonds the aggregate to the pavement surface, leaving a thin pavement surface treatment that 

can be applied during a short closure (e.g., 6-8 hours) of the roadway. 

• HFST is not a structural overlay or a pavement preservation treatment and is not known to 

provide any extension of pavement life which can be found with microsurfacing, slurry seals, 

and chip seals. It simply enhances the friction of an existing pavement surface using materials 

and installation methods unique to the treatment.

2. What is the purpose of HFST?

• HFST enhances the ability of a pavement surface to provide adequate friction (i.e., friction 

supply) at locations with high friction demand, thereby increasing the margin of safety. If friction 

demand exceeds friction supply, vehicle skidding is likely to occur. A combination of pavement 

macrotexture (which allows water to evacuate from beneath vehicle tires, particularly at higher 

speeds) and microtexture (which provides the actual tire-pavement contact) contributes to good 

pavement friction. HFST provides exceptional friction supply through this combination of 

macrotexture and microtexture. Please refer to FHWA’s HFST Site Selection and Installation 

Guide for additional information on friction demand, friction supply, and margin of safety 

concepts.

https://safety.fhwa.dot.gov/roadway_dept/pavement_friction/high_friction/docs/HFST_Guide_

HPA.pdf

• Locations with high friction demand include horizontal curves, ramps, steep grades, and 

intersections where greater friction is needed to help keep vehicles on the road and reduces 

stopping distance, particularly in wet weather. In locations such as sharp horizontal curves, 

where vehicles apply higher side-shear force to the pavement, the pavement surface tends to 
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polish faster, reducing pavement friction supply and the margin of safety. Reduced friction can 

contribute to vehicles losing control or skidding when they are traveling at excessive speed, 

making abrupt turns, or braking excessively. Higher friction, maintained with polish-resistant 

aggregates such as calcined bauxite, helps to prevent skidding and reduce stopping distance

under both wet and dry roadway conditions. 

• HFST can help compensate for deficient geometric designs, such as sharp curves and/or 

inadequate or variable superelevation, by providing the necessary friction to maintain traction 

on the intended path. 

• HFST has been used successfully in lieu of costly roadway realignments, which can take years to 

complete due to delays associated with lengthy planning phases and budget constraints, and 

may also necessitate lengthy traffic detours during construction. With the short construction 

duration, HFST can begin reducing crashes and saving lives immediately as opposed to several 

years later for a realignment project. 

3. How are potential HFST sites identified?

• The two primary approaches for HFST candidate site identification currently used in the United 

States are the site-specific safety approach and systemic approach. 

• The site-specific safety approach, also known as a hot-spot approach, is a reactive approach 

which uses site-specific crash data to identify locations where a countermeasure is needed. 

Reacting to crashes is a simplified version of this approach, but more advanced approaches use 

historic crash data and predictive methodologies such as safety performance functions (SPFs) 

and Empirical Bayes (EB) to identify locations where HFST may provide benefit. These advanced 

approaches help identify sites over-represented with target crashes, typically run-off-road and 

wet weather crashes, for individual installations. 

• The systemic approach is a more proactive approach to treat locations deemed “high risk” for 

friction-related crashes. Predictive methods, such as SPFs, help practitioners to identify high-risk 

features. Locations are identified based on the presence of several different risk factors such as 

roadway characteristics, traffic exposure, and pavement friction. This approach treats a broader 

series of sites based on the risk of target crashes at locations that may not have historically 

observed crashes but are at higher risk for future crashes.

• Pavement friction management programs (PFMPs) utilizing appropriate testing methodologies 

and devices, such as continuous pavement friction measurement (CPFM), are another proactive 

approach to identify potential friction issues before they manifest in the form of increased crash 

rates. 

4. What are recommended limits for HSFT installations?

• While there are general recommendations for treatment limits (e.g., from point of curvature to 

point of tangency for curve locations), the final decision for a particular site should be as data-
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driven as possible. Verification of candidate sites through friction testing and field reviews will 

help with the establishment of treatment limits. 

• Friction testing of the candidate location, including pavement upstream and downstream from 

the proposed location (when possible), will help identify changes in friction leading up to, 

through, and away from the targeted treatment area such that treatment limits can be adjusted 

based on pavement friction. CPFM technologies provide a comprehensive “map” of pavement 

friction for identifying changes in friction at candidate locations. A margin of safety assessment 

can be further used to establish appropriate treatment limits based on site conditions. 

• The Texas A&M Transportation Institute published the "Pavement Safety-Based Guidelines for 

Horizontal Curve Safety” for a margin of safety analysis of horizontal curves. This report can be 

found at: https://static.tti.tamu.edu/tti.tamu.edu/documents/0-6932-R1.pdf

• Field reviews will provide a better understanding of driver behavior at a candidate location for 

the purpose of establishing treatment limits. Field reviews should include physically locating 

reported crashes and observing driver behavior (ideally under the same conditions when most 

crashes have occurred), to determine where vehicles begin to brake in advance of the curve, 

ramp, or intersection.

• Additional considerations for treatment limits include a determination of whether only one lane 

or direction need to be treated, whether adjacent paved shoulders need to be treated, and 

whether a treatment should be continued through multiple-curve locations rather than leaving 

short areas untreated between curves. 

• HFST may be placed within the width of the traveled lane only or from edge of pavement to 

edge of pavement. The treatment may also be applied to an area that is narrower than a lane to 

avoid removal of striping or pavement markings. This decision should be evaluated in the design 

phase of the project with respect the project budget, the behavior of vehicles, and the relevant 

crash data. Placement within the traveled lane only may result in lower required quantity of 

HFST, but may not provide enhanced friction on shoulders if traffic patterns or crash data 

indicate that vehicles travel partially within the shoulder area–behavior which is common on 

tight curves and ramps. It is generally not necessary to place HFST within 1 foot of obstructions 

to traffic like barriers, guardrail, or attenuators. When placing HFST on paved shoulders, it is also 

not usually necessary to follow a variable or degraded roadway edge exactly, but rather to 

establish a path that provides for a consistent width for friction enhancement.

SAFETY

1. Are there any crash modification factors (CMFs) available for HFST?

• CMFs are available for HFST curve and ramp applications from an FHWA study conducted as part 

of the Evaluation of Low-Cost Safety Improvements Pooled Fund Study. This study generated 

high-quality and robust CMFs and benefit-cost ratios for HFSTs with calcined bauxite aggregate 
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based on data-driven before- and after-crash data analysis to quantify crash reduction benefits. 

CMFs are provided for total, injury, run-off-road, wet road, and head-on side-swipe opposite 

direction crashes for curves and total, injury, run-off-road, and wet road crashes for ramps. 

Through a disaggregate analysis of the before-after evaluation data for curves this study also 

reports CMFs for HFST based on friction increase, traffic, and annual crash rates. This report can 

be found at: https://www.fhwa.dot.gov/publications/research/safety/20061/index.cfm

• Table 1 summarizes the CMFs for ramp locations from this FHWA study. While these are the 

only 4- and 5-star CMFs in the Crash Modification Factors Clearinghouse, others are also 

available: https://www.cmfclearinghouse.org/index.cfm

Table 1. CMFs for HFST on Curves.

Crashes after treatment application

Crash Type Observed EB Expected CMF (s.e.)

Total 329 767.84 0.430 (0.028)

Injury 106 205.02 0.515 (0.037)

Run-off-road 92 333.49 0.279 (0.032)

Wet road 82 495.54 0.168 (0.020)

HOSSOD 59 81.29 0.691 (0.105)

Note: CMF = crash modification factor; EB = empirical Bayes; HOSSOD = head-on side-swipe opposite direction; s.e. = 

standard error. CMFs that are statistically significant at the 5-percent level are indicated in boldface. EB expected is an 

estimate of the number of crashes the sites would have experienced had HFST not been installed.

2. What are the advantages of using HFST compared to using traditional safety treatments 

at horizontal curves?

• HFST should be considered when delineation treatments such as pavement markings, signage, 

etc. are not reducing crashes, and pavement friction is suspected to be inadequate for 

prevailing conditions. Generally, signs and markings are effective for prudent drivers who are 

trying to drive carefully, but when vehicles enter a curve too fast it is generally too late for 

those devices to help the driver. Whether some drivers are willfully speeding or distracted 

and the curve surprises them, speed is a major contributing factor for crashes in curves. Many 

studies have shown that a pavement with high skid resistance can give drivers a "hidden 

advantage" and help them still navigate the curve. 

• If the pavement is polished or has lower skid resistance to begin with, safely navigating the 

roadway can become a problem even for prudent drivers, particularly when the pavement is 

wet. HFST provides a pavement that is polish-resistant and has excellent friction. Other safety 

enhancements may require geometric improvements, which can take a long time, be 

expensive, increase delay and safety risks associated with lengthy active work zone periods, 

and have environmental consequences. By comparison, HFST costs less and has fewer of 

these impacts.
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3. What is the safety effect of these surfaces for motorcycles and bicycles?

• There are no known negative safety effects for motorcycles and bicycles. In fact, braking and 

cornering on a motorcycle demand more friction than similar maneuvers do for passenger 

vehicles, so HFST can be even more impactful in improving motorcycle safety on curves and 

intersection approaches.1 

• In the State of Rhode Island, HFST was installed on a curve that had eight motorcycle crashes 

in five years. Since HFST installation in 2014 there have been no reported motorcycle 

crashes.1

• One recommended precaution related to motorcycles and bicycles is to ensure that all loose 

aggregate is thoroughly removed from the HFST and surrounding surfaces before opening to 

traffic as loose aggregate can have a more detrimental impact on motorcycles and bicycles. 

This includes subsequent re-sweeping as needed in the first few weeks after installation as 

the HFST naturally sheds aggregate under traffic. Agencies may consider leaving “loose 

gravel” warning signs in place for the first 30-60 days after installation as a precaution. 

• To date, no problems with abrasiveness have been identified regarding bicycle use on HFST. 

This product has been used widely for many years in Europe and in many other countries that 

have large bicycle populations and this has not been an issue. In fact, the HFST process is used 

to install colored aggregate (not calcined bauxite) that serves as demarcation. This product 

has been requested by bicycle groups for bike lane surfaces because the texture helps reduce 

the problem of tires sliding when wet, which is common on some demarcation treatments.

4. Has there been an increase in truck rollovers after installation?

• No increase in truck rollovers has been reported from any HFST installations, and studies by 

FHWA in the past have shown that increases in friction help reduce truck rollover, in part by 

keeping trucks from running off the road where rollovers typically occur. Illinois DOT observed 

a reduction in truck rollovers on tight-radius ramps where HFST was installed. 

• Illinois DOT also observed a substantial reduction in semi-truck roadway departure crashes on 

a tangent section of interstate highway with strong cross winds after HFST was applied. HFST 

appears to provide semi-trucks better ability to regain control.

5. What effect does HFST have on braking distance and stopping behavior at intersections?

• Depending on the level of friction of the existing pavement surface, HFST can increase the 

coefficient of friction by 200 percent or more. In theory, using the basic equation for braking 

distance (not accounting for site distance, grade, etc.), increasing friction by 50 percent will 

decrease stopping distance by one third, doubling friction will decrease stopping distance by 

one half, and tripling friction (e.g., 200 percent increase) will decrease stopping distance by 

two thirds, regardless of speed. These stopping distances will vary widely based on real-world 
9 

conditions (pavement surface condition, pavement texture, tire tread condition, driver 

behavior, etc.), but this is a general indication of the potential reduction in stopping distance. 

• The University of South Florida’s Center for Urban Transportation Research evaluated changes 

in driver behavior at intersections before and after HFST was applied. Using video footage 

from the intersections, the number of crosswalk incursions at a red light were documented as 

improper stopping behavior. Evaluations were performed at multiple times of the day before 

and after HFST was applied. For one intersection the analysis revealed a 26 percent reduction 

in improper stopping behavior one month after HFST application and 31 percent after nine 

months, indicating that the effects are sustained over time.2

MAINTENANCE AND OPERATIONS

1. Does HFST promote higher operating speed?

• HNTB Corporation monitored speeds after an HFST installation for the Florida DOT and found 

that speeds post-installation were lower under both wet and dry conditions. The report can be 

found at: https://fdotwww.blob.core.windows.net/sitefinity/docs/defaultsource/research/reports/bd500-v3-rpt.pdf?sfvrsn=d0ae33a5_2

• While increasing superelevation does increase driver comfort, and improving driver comfort 

usually does increase speeds, there is no evidence that installing HFST leads to increased speed. 

HFST only satisfies friction needed to help the vehicle stay on the road without changing existing 

superelevation. 

• Regardless of speed considerations, there have not been any notable increases in crashes on 

treated segments. All of the crash evaluations to date have shown remarkable crash reductions, 

which is the goal. 

2. What is the effect of snowplows on this pavement treatment? 

• Because HFST is such a thin overlay, generally less than 1/4-inch in thickness, the effect from 

snowplows has been minimal, even where "bare pavement" policies are followed in states such 

as Illinois, Vermont, and Michigan.

• Calcined bauxite aggregate wears very well under heavy snow plowing, and no deterioration 

from steel-tipped plows has been observed. HFST has been placed in many areas that see heavy 

snowplowing and winter weather, including Alaska, Pennsylvania, and South Dakota.

• South Dakota implemented HFST specifically to help reduce roadway departure crashes 

involving winter road conditions. Three years after installation of four initial demonstration 

1 Geary, G., K. Dixon, K. Aspelin, and M. Manser. Addressing the Motorcyclist Advisory Council Recommendations: 

Synthesis on Roadway Geometry, Pavement Design, and Pavement Construction and Maintenance Practices. 

Report No. FHWA-SA-21-090. US Department of Transportation, Washington, DC., Nov. 2021. 2 Merritt, D and S. Himes. Improving Pavement Friction for Safety at a Florida Signalized Intersection. Report No. 

FHWA-SA-22-10. Federal Highway Administration, Washington, DC., Nov. 2021.
10

project, South Dakota DOT reported an 80 percent crash reduction. And two years after

installation at 15 additional locations, they reported a 78 percent reduction in crashes. 

https://safety.fhwa.dot.gov/roadway_dept/pavement_friction/case_studies_noteworthy_prac/

docs/SD%20HFST%20Noteworthy%20Practice.pdf

3. Can HFST be applied in conjunction with rumble strips?

• There are no known issues with applying HFST in conjunction with rumble strips. In fact, because 

they serve different purposes (rumble strips alert the driver to lane departure and HFST 

provides additional traction for potential evasive recover maneuvers) they will complement one 

another as a redundancy practice under the Safe System Approach. 

• If rumble strips already exist on the roadway where HFST is to be applied, avoid placing HFST 

over the rumble strips (i.e., mask off the rumble strips) since the resin binder will flow down into 

the rumble strips, potentially filling the rumble strips and reducing resin binder thickness on the 

surface. If rumble strips are to be installed after HFST, the HFST should be applied as usual and 

the rumble strips milled into the pavement through the HFST after the resin binder has fully 

cured (e.g., minimum 24 hours after placement). Similarly, recessed striping and recessed 

markers may be installed by grinding through the HFST with milling equipment.

4. Does HFST accelerate tire wear?

• Excessive tire wear should not be an issue since HFST is applied only at spot locations for smaller 

areas. The safety benefits of HFST likely far outweigh tire wear as a concern.

• Illinois DOT reported receiving a few complaints from the public regarding perceived tire 

damage, but no further action was taken. 

5. What maintenance is required for HFST?

• A properly installed HFST should not require any routine maintenance typical of conventional 

pavement surfaces. However, if there is evidence of issues with the underlying pavement, such 

as subgrade pumping, potholes, alligator cracking, etc. conventional maintenance treatments 

such as crack sealing, pothole patching, and isolated repairs may be necessary to mitigate failure 

of the underlying pavement. 

• HFST surfaces should be routinely monitored similar to conventional pavement surfaces if there 

is concern with dirt/debris buildup, leaf buildup, etc. The surface should be cleaned to maintain 

pavement macrotexture using the same methods as that for conventional pavement surfaces. 

• Note that the effectiveness of HFST should not be judged based on surface appearance. An HFST 

surface that is showing signs of wear may still have excellent friction characteristics and would 

not necessitate replacement.
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6. How is HFST removed and can it be recycled?

• HFST is typically removed with conventional milling processes. If only the HFST is to be removed 

and not the underlying pavement, micromilling or diamond grinding processes are 

recommended. 

• If HFST is to be removed with the underlying pavement, it can be milled up and recycled with 

the underlying pavement. Because it is such a thin surface treatment, the amount of HFST 

should not affect the properties of the recycled material.

COST

1. What is the average unit cost for HFST?

• Installed costs vary widely based on a number of factors related to agency contracting 

mechanisms, materials, and installation methods. Most projects are solicited as turnkey, and 

include mobilization, materials, labor, equipment, and traffic control. Please refer to the FHWA 

HFST Site Selection and Installation Guide for additional information on HFST cost and contact 

owner agencies for current bid prices. 

• The cost per square yard has steadily decreased for larger projects and smaller projects which 

have been bundled together or with other safety-related items. Only including work pertinent to 

the HFST project, therefore increasing the chance of contracting directly with an established 

installer, can help reduce costs. In general, unless unavoidable, HFST projects should be standalone and not added onto paving or other related work through prime contracts, as the unit 

price for HFST can increase because of the additional percentages added by the general 

contractor. 

• Many design and specification-related factors can contribute to the cost of the project. The 

larger the scope of the project, the lower the unit cost is likely to be. The proximity of locations 

to one another, time constraints on installation, and the cost of excessive material and 

acceptance testing will also impact project cost. 

2. What is the benefit-cost ratio for HFST?

Published benefit-cost ratios (B/C) vary widely, based primarily on the processes used for site selection 

and the types of crashes (e.g., fatal and injury vs. property damage only) HFST is used to mitigate. 

PennDOT, the Kentucky Transportation Cabinet (KYTC), and Florida DOT all track project costs closely 

and regularly compute benefit-cost ratios. Based on a 2018 evaluation of 47 locations which had been in 

place for 3-5 years, PennDOT reported a B/C of 5.5 for all crashes and 2.4 for wet road crashes based on 

the KABCO scale and FHWA crash costs. KYTC has realized B/C greater than 30 for the past two years (as 

of 2021), and Florida DOT has reported an average 5-year B/C of 24.5 on tight curves using the KABCO 

method. 

https://safety.fhwa.dot.gov/roadway_dept/pavement_friction/case_studies_noteworthy_prac/docs/PA

%20HFST%20Noteworthy%20Practice.pdf
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3. How should the cost of HFST be evaluated?

Although it is a pavement surface treatment, any life-cycle cost evaluation of HFST should consider the 

benefit-cost from crash reduction as a safety countermeasure. While HFST is a low-cost safety 

countermeasure when compared to treatments such as roadway geometric improvements, it is 

generally not competitive based on first cost or even life-cycle cost with other low-cost safety 

countermeasures and pavement treatments when solely considering the cost of the treatment. 

However, when the safety benefit is considered (see benefit-cost ratios, above) in a life-cycle cost 

analysis, HFST is highly competitive.

ENVIRONMENTAL 

1. What effect does HFST have on road noise?

• In general, HFST will be less noisy than transversely tined concrete pavement, chip seals, and 

certain dense-graded asphalt pavements. While HFST does increase macrotexture depth, the 

relationship (for all types of pavement surfaces) between macrotexture depth and noise level is 

extremely weak. Therefore, it is not a valid conclusion that higher texture depth will lead to 

more noise.

• Some noise reductions and pavement color changes may be perceived by drivers, especially on 

curves, which may tend to cause a reduction in average speeds. However, additional research in 

this area would be needed to substantiate or refute this question.

• Overall, since most HFST installations only span from the point of curvature (beginning of the 

curve) to the point of tangency (end of the curve), the difference in the sound level produced by 

driving over the HFST will only last for a few seconds, and then the vehicle will be back on the 

regular pavement surface.

• Limited testing of tire-pavement noise by The Transtec Group on two HFST sections (one in 

Kansas and one in Montana) approximately one year after they were installed indicated that 

HFST applied over chip seal was slightly quieter (expressed as overall onboard sound intensity 

(OBSI) in A-weighted decibels (dBA)):

3

 

o Chip seal:  ̃104.4

o HFST:  ̃101.95

For the HMA, HFST was slightly louder:

o HMA:  ̃98.75

o HFST:  ̃100.05

3 Merritt, D. and M. Moravec. Performance of High Friction Surfacing Demonstrations in the U.S. Proceedings of 

the 7th Symposium on Pavement Surface Characteristics: SURF 2012. Norfolk, VA. Sept. 2012.
13

Note: 3 dBA is essentially the minimum threshold for human-perceived change in noise level.

• The Kansas Department of Transportation further studied possibility of using HFST to reduce 

roadway noise through the construction and testing of an HFST test section.4 This study 

revealed that HFST produced only a small decrease in exterior road noise ranging from 2.6 to 3.1 

dBA. However, this study noted that HFST changed the tonal frequency of tire-pavement noise, 

such that noise was less offensive to the human ear. 

2. What are some of the potential environmental benefits for HFST?

• No physical reconstruction of road surface so no inadvertent changes in drainage patterns.

• No increase in impervious area footprint.

• Short construction timeframe results in less chance of environmental-related mishaps during 

construction.

• Minimal footprint for staging and construction. 

• Installation eliminates complete road closure and lengthy detours due to HFST’s capability of 

being applied one lane at a time, resulting in less pollution due to congestion and less traffic 

delay. 

• Please refer to a case study highlighting a successful installation of HFST by Caltrans in an

environmentally sensitive area: https://safety.fhwa.dot.gov/roadway_dept/pavement_friction/ 

case_studies_noteworthy_prac/nocal/

4 Linden, E., M. Stewart, S. Embers, S. Cho, and K. Wanklyn. Use of High Friction Surface for Highway Noise 

Reduction. KDOT Report No. KS-18-01. Kansas Department of Transportation. Topeka, KS. May 2018.
14

MATERIAL SPECIFICATIONS / DURABILITY

1. What is the life expectancy of HFST?

• The condition of the pavement over which the HFST is installed and the quality of the HFST 

installation will likely have the biggest impact on life expectancy. For a properly-installed HFST 

over structurally-sound pavement, life expectancy will vary with climate and roadway 

characteristics, such as geometry, volume and mix of traffic, and the nature of traffic 

movements. Accordingly, it is difficult to generalize. 

o Due to its relatively recent adoption in the United States, a limited number of HFST 

installations are older than 10 years, but there are a number of installations throughout 

the country that are still intact and performing well in reducing crashes after 8-10 years 

of usage without failure. 

o HFST testing on test tracks with accelerated aging/loading has shown some HFST 

sections continuing to last and provide friction enhancement capability with over 30 

million equivalent single-axle loads (ESALs) of wear. 

https://eng.auburn.edu/research/centers/ncat/files/technical-reports/rep18-04.pdf

https://eng.auburn.edu/research/centers/ncat/files/technical-reports/rep15-04.pdf

o International experience indicates at least 7-12 years of service can be expected with 

correctly applied installations. The Road Surface Treatment Association from the United 

Kingdom reports an average service life of 12 years for cold applied HFST, such as those 

used in the United States.5

 

• Just like pavement performance, HFST longevity is dependent on many factors, such as initial 

construction quality, friction demand, and traffic volume as well as the severity of the climate 

and the weight and number of heavy truck axles using the facility.

• Proper installation is critical to longevity and includes ensuring uniform application of adequate 

resin binder mil thickness and timely application of the aggregate to achieve adequate 

embedment.

• Vehicular traffic with heavy chains or studded tires will increase wear within the wheel path of 

the HFST.

• As a treatment used specifically to improve pavement friction, remaining life should be 

evaluated based on friction and not just treatment condition. Although an HFST may appear 

visibly worn and distressed, it may still have excellent friction characteristics and therefore still 

5 RSTA ADEPT. Code of Practice for High Friction Surfacing, 2nd Edition. Road Surface Treatment Association. United 

Kingdom. 2017.
15

be effective as a safety countermeasure. Even when HFST is worn in the wheelpaths, but still 

intact outside of the wheelpaths, it will still provide benefit for reducing lane departures.

2. Are these materials resistant to fuels and common de-icing agents?

HFST installations are resistant to both fuel spills and deicing chemicals in roadway environments. Once 

cured, the polymer resin will remain stable even when exposed to incidental levels of solvents or diesel 

fuel, for example.

3. What is the difference between HFST and other pavement preservation treatments such as 

microsurfacing and chip seal?

• HFST is a safety treatment used specifically to enhance pavement friction, primarily for spot 

locations with high friction demand such as severe curves and braking areas. By using calcined 

bauxite, which is a manufactured aggregate with exceptional abrasion and polish-resistance, 

high friction test results are maintained over time. Installed HFST friction test results (from 

locked-wheel skid testing and continuous friction measurement) are over 70 and many times in 

the high 80s or low 90s. The HFST resin binder material is a thermosetting, polymer-based 

material, providing an 8-12 year friction-enhancing treatment.

• Other treatments such as microsurfacing and chip seal/seal coat are pavement preservation 

treatments that may also improve skid resistance, but are generally used primarily to extend the 

life of the pavement. These treatments produce initial friction readings generally lower than 

HFST, and that friction generally declines with time due to raveling, flushing, or polishing of the 

aggregate. Please refer to FHWA Turner-Fairbank Highway Research Center (TFHRC) publication 

titled "Evaluation of Pavement Safety Performance," which included a description of various 

pavement treatment types. The publication is available at: 

https://www.fhwa.dot.gov/publications/research/safety/14065/14065.pdf.

4. Is it worth the investment to use HFST compared to other friction treatments?

• The answer to this question depends on the condition of the existing pavement and the severity 

and type of crashes at the candidate location. For a deteriorating pavement with substandard 

friction characteristics and minimal pavement life remaining, more conventional pavement 

treatments will help extend pavement life and restore standard friction characteristics for the 

short term. However, if crash data indicates that a higher level of friction is needed immediately, 

HFST may be more appropriate, even if it will only provide a short-term solution due to the 

condition of the existing pavement. 

• HFST can also provide an immediate low-cost remedial solution for locations where geometric 

issues exist (e.g., inadequate superelevation, curve radius, site distance, etc.), until the more 

costly geometric improvements can be made. 
16

• In general, while many pavement preservation treatments (microsurfacing, chip seal, etc.) can 

improve pavement friction, they will not provide the same level of friction, sustained over time, 

as HFST.

5. Do these materials crack? If so, how do they resist crack erosion?

• The materials typically do not crack on their own, but any cracks (and joints) in the underlying 

pavement will generally reflect through. 

• If there is concern with erosion (pumping of subbase fines) at reflected cracks, these cracks can 

be sealed using conventional crack-sealing methods, ensuring that the sealant is recessed 

slightly below the top surface of the HFST and not overbanded onto the HFST.

6. Are there any issues with thermoplastic on HFST?

• No. Thermoplastic bonds extremely well and will in fact last longer when applied to the textured 

surface of HFST. Other marking materials also bond well, but pavement marking tape should be 

avoided since it does not adhere well due the textured surface of the HFST.

• Masking of existing thermoplastic striping and markings prior to HFST application will save the 

cost of removal and replacement of the thermoplastic, especially if the existing markings are in 

good condition. Any masking should be removed immediately after HFST application before the 

resin binder begins to harden.

7. What aggregates are appropriate for HFST and what sources are available?

• Refractory-grade calcined bauxite is the only HFST aggregate permitted by most agency 

specifications and the current AASHTO HFST specification (note that following this specification 

is not required by Federal law or regulation). Calcined bauxite has a decades-long proven track 

record of providing exceptional polish and abrasion resistance properties necessary for HFST. 

While there may be other natural aggregates that can provide satisfactory friction initially, the 

mineralogical and physical properties of engineered calcined bauxite aggregate makes this the 

only material proven to maintain high levels of friction over time. While calcined bauxite 

aggregate is traditionally imported from overseas, there are also domestic sources available. 

• Alternative aggregates can be applied in a similar manner and may perform adequately in a less 

demanding environment, but in critical locations they have not provided the friction durability 

to be classified as HFST. Other aggregates, such as flint, basalt, taconite and granite have and 

continue to be evaluated for performance, but at this time only calcined bauxite is 

recommended by FHWA for providing the expected safety performance and durability required 

in an HFST application. 

• Please refer to Question 11 below for several HFST aggregate durability studies related to 

aggregate testing from the National Center for Asphalt Technology (NCAT).
17

8. Can reclaimed aggregate be reused and are there any special requirements for disposal?

• During the HFST installation process, the calcined bauxite aggregate is applied “to refusal” over 

the wet resin binder. This results in excess aggregate material that does not adhere to the resin 

and is swept up and reclaimed prior to opening the treated area to traffic. 

• Use of reclaimed aggregate material should be considered very carefully. HFST aggregate is 

supplied to a specific gradation and, if not managed carefully, the process of reclamation may 

result in a material that does not meet the grading specification. Generally, reclaimed aggregate 

will have a finer gradation (i.e., higher proportion of smaller particles and dust) than virgin 

material. Smaller aggregate particles will not provide the same frictional properties, and 

excessive dust will inhibit embedment of actual aggregate particles into the resin binder during 

application. 

• If reclaimed aggregate is acceptable within an agency’s specification, then the following should 

be considered: 

o Place only enough aggregate material to completely cover all wet resin binder without 

undue excess material. Note that fully-automated application processes tend to control 

application rate better than manual application. 

o Clean treated and adjacent surfaces (e.g., adjacent lanes and paved shoulders)

thoroughly prior to HFST application and do not attempt to reclaim HFST aggregate from 

unpaved shoulder/gravel edges to prevent the introduction of foreign material into the 

reclaimed material. 

o All recovery sweeping equipment should be thoroughly cleaned and inspected prior to 

the sweeping operation to prevent the introduction of foreign matter into the reclaimed 

aggregate. 

o Upon completion of the sweeping operation, estimate the accumulation weight and 

obtain a representative test sample to identify the gradation of the reclaimed material.

o Complete and record gradation tests of the reclaimed aggregate. If necessary, require 

that the reclaimed aggregate be washed or sieved to reduce dust and smaller aggregate 

content. Reclaimed aggregate should not be introduced in lower dilution ratios than one

part of reclaimed aggregate to two parts of prime (virgin) aggregate. Reintroduction 

should only be performed using methods that will ensure complete blending of

reclaimed aggregate with virgin aggregate. 

• Calcined bauxite is an inert and non-toxic material. Therefore, disposal of recovered or excess 

aggregate material should follow standard practices for conventional aggregate materials.
18

9. What are some typical polished stone values (PSV) for HFST aggregates using ASTM E 

303/AASHTO T 278 British Portable Pendulum Tester and ASTM D 3319/AASHTO T 279 British 

Wheel Accelerated Polishing Machine?

• Testing HFST aggregate for PSV is fairly common practice. However, keep in mind that PSV 

testing used in Europe based on the British method (EN 1097-8) is different than the ASTM 

method (ASTM D 3319/AASHTO T 279) even though the testing apparatus is the same. Also, the 

gradation of aggregate specified for PSV testing per ASTM is different than that commonly 

specified for HFST. This requires a modification of the test method that has not yet been defined 

within the ASTM. In order to use the PSV requirement for high-friction aggregates within a 

specification, a value greater than 40 will be required. This value is determined by using the 

primary "main scale" of the British Pendulum rather than "F-scale" which is used when 

measuring PSV in accordance with the British (EN 1097-8) test method. Use of these testing 

procedures is not required under Federal law or regulation.

• The Micro-Deval Apparatus (MDA) is another test method used to evaluate abrasion and polish 

resistance of HFST aggregates in accordance with ASTM D 7428. The AASHTO specification 

recommends a maximum of 5 percent mass loss using this test method (note that the use of

these testing procedures is not required under Federal law or regulation).

10. Several HFST aggregate durability studies were published in cooperation with FHWA and 

the National Center for Asphalt Technology (NCAT):

• High Friction Surface Treatment Alterative Aggregates Study 

https://eng.auburn.edu/research/centers/ncat/files/technical-reports/rep15-04.pdf

• Evaluation of Laboratory Friction Performance of Aggregates for High Friction Surface 

Treatments https://www.eng.auburn.edu/research/centers/ncat/files/technical-reports/rep17-

01.pdf

• Evaluation of the AIMS2 and Micro-Deval to Characterize Aggregate Friction Properties 

https://www.eng.auburn.edu/research/centers/ncat/files/technical-reports/rep17-02.pdf

11. Can HFST be placed on a bridge deck? 

• HFST can be applied to bridge decks. In fact, the concept for HFST originated in the U.S. as a 

polymer overlay bridge preservation treatment. However, while the polymeric resin binder and 

installation methods used for polymer bridge deck overlays are similar to that used for HFST, 

polymer bridge deck overlays are used primarily to help seal and protect the bridge deck, with 

friction as a secondary benefit. The common practice for bridge deck overlays is to apply a 

double layer of resin binder and aggregate for insurance against water penetration of the deck, 

and to provide added durability to the surface. 

• If a bridge is in a curve and identified as having a crash problem, a double layer of HFST could be 

substituted for a conventional bridge deck polymer overlay and accomplish both purposes—
19

protection and crash reduction. This has been done in many locations across the country, 

especially on roadways or ramps where an adjacent roadway segment is considered for HFST. 

Many interchanges and ramps, for example, may have non-standard geometry resulting in crash 

problems on both bridge and roadway segments. An HFST treatment applied to both would 

allow for friction enhancement and crash reduction regardless of the underlying roadway type.

12. Are HFST systems proprietary? 

In general, all HFST equipment and materials are commercially available, although the resin binder 

formulations are proprietary. There may also be proprietary components to certain application 

equipment. Some agencies will install HFST with their own maintenance crews, which will likely 

necessitate manual placement methods, and should therefore be limited to smaller applications.

13. Is there a certification process for contractors who want to perform this type of work or 

training resources for agency inspectors?

• Currently there are no certification processes for HFST installation. A robust project specification 

makes worker knowledge and experience less of a factor in the quality of the end product.

• The best way to address the issue of contractor performance is to develop a robust project 

specification that requires previous HFST installation experience, completion of a test strip to 

demonstrate installation, and several quality checks. These project requirements hold the 

bidders accountable for meeting the specifications for a proper installation. 

• Inspector training is another way to help ensure that inspectors better understand what to 

watch for during installation. Including a requirement for training of project inspection 

personnel in the project specification through a “just-in-time-training” approach is 

recommended to help ensure project inspectors receive the necessary training. With this 

approach, project specifications/special provisions include a requirement for training of project 

inspectors. As such, the cost of training is included in the project itself and the designated 

project inspectors can be trained just prior to HFST installation. At least one vendor offers an 

HFST installation and inspection training course that can be used for this purpose. FHWA also 

provides training materials and is working diligently to try to help State agencies write a better 

specification to cover some of these concerns. 

• FHWA has produced a pocket installation guide with inspection checklist that can be 

downloaded from the website below and viewed on a mobile device in the field if needed. 

https://safety.fhwa.dot.gov/roadway_dept/pavement_friction/high_friction/

14. Are there specifications for HFST? 

• The AASHTO Standard Specification, High Friction Surface Treatment for Asphalt and Concrete 

Pavements Using Calcined Bauxite (MP 41-19) is available for agencies to adopt in whole or in 

parts to their construction specifications. Use of this specification is not required by Federal law 

or regulation.
20

• Many State and local agencies now have mature specifications or special provisions for HFST 

that have been revised over time based on their experience. Standard specifications and special 

provisions used in states such as California, Delaware, Florida, Georgia, Illinois, Kentucky, 

Louisiana, Maryland, Pennsylvania, South Carolina, Tennessee, and Texas are often used as 

reference points for agencies that are developing their own standards for HFST.

LESSONS LEARNED

1. What are the lessons learned with HFST installation?

• Common issues contributing to installation problems are due to one or a combination of the 

following practices: 

o Improper mixing of the resin binder system, either manually or by automated 

equipment that did not have fail safes or monitoring devices. This can result in resin 

binder that does not properly cure, leading to early loss of aggregates and premature 

wear in the wheelpath. Installations for which resin binder manufacturer instructions 

have not been followed can encounter problems.

o Improper placement of the resin binder by applying it either too thin or too thick or by 

disturbing the resin after it has begun its gel phase. 

 If the resin material is placed too thin, it may not have sufficient depth to 

embed and retain the aggregate for long-term durability. Proper resin binder 

thickness should be indicated based on pavement macrotexture depth. 

 If the resin material is placed too thick, it may fully encapsulate the aggregate 

material, leading to a lower friction (glassy) resin surface and lower 

macrotexture to channel water away. A thick resin binder layer can also lead to 

higher shear stresses at the HFST-pavement interface, which can lead to 

delamination or substrate failure. When the material is placed on steep grades 

or banked roadways, it may also exhibit creep or drift towards the lower side of 

the roadway during curing, leading to an unevenly thick resin binder layer. 

 If the resin is disturbed after placement as it begins to build its strength in the 

gel phase, it may lead to a reduction in the strength properties of the final cured 

resin material. Sweeping excess aggregate too soon, before it has properly 

cured, can lead to aggregate loss and exposed pavement.

o Application of aggregate after resin binder has begun to gel. Aggregate should be 

broadcast onto the resin binder immediately to ensure proper embedment. Resin 

binder tends to gel very fast at high temperatures, and gelled resin binder will resist 

aggregate penetration. This is a primary advantage of automated continuous application 

systems which broadcast the aggregate within seconds after placement of the binder 

resin. 
21

o Improper embedment depth. Embedment depth should typically be 50 percent of the 

nominal aggregate size to ensure that the aggregate is held firmly in place by the resin 

binder while still providing adequate texture for frictional resistance and bulk water 

drainage. Embedment is affected by resin binder application rate which is dictated by 

pavement macrotexture depth. 

o Application of HFST to newly-constructed pavements. HFST should not be applied to 

asphalt or concrete pavements that are less than 30 days old. This allows for release of 

oils, volatile organic compounds, etc. For concrete pavement, all curing compounds 

should be removed and the surface properly shot-blasted. Shotblasting removes 

concrete surface contaminants and increases macrotexture to facilitate bonding of the 

resin binder.

o Application of HFST to pavements in poor condition. Highly distressed pavements 

exhibiting extensive cracking, raveling, flushing, and subbase pumping will likely fail 

beneath the HFST under traffic and over time. Failure of the underlying pavement will 

result in failure of the HFST even when the resin binder and aggregate remain bonded to 

the failing pavement. 

o Environmental requirements were ignored. The pavement surface should be dry at time 

of installation, and the ambient and surface temperature should be above the 

manufacturer’s minimum recommendation. For most polymer resin binders, a minimum 

temperature of 50°F and rising is typical, while some recommend even higher minimum 

temperatures. Other polymer binders are available that can be installed at lower 

temperatures per the manufacturer’s direction. Please see general temperature 

conditions under INSTALLATION.

2. What pavement conditions caused failures that have been reported?

• Highly distressed pavements. Pavements exhibiting extensive durability-related cracking such as 

alligator, block, and map cracking. Any pattern cracking that is visible on the pavement likely 

makes the pavement a poor candidate for an HFST installation.

• Pavements exhibiting rutting, shoving or signs of subgrade failure are likely poor candidates for 

HFST. 

• Poorly draining pavements. Pavements in sag curves with poor drainage and curb and gutter 

locations where water tends to collect. Pavements exhibiting subsurface moisture issues and the 

migration of subgrade fines have also led to premature failure of the underlying pavement and 

HFST and therefore are poor candidates for HFST. Subsurface moisture issues may not be 

present and obvious at all times and therefore should be checked after rain events.

• Chip seal (seal coat) in poor condition. Chip seal or seal coats exhibiting raveling or flushing in 

the wheel paths has led to failures. While HFST will adhere to flushed surfaces, the bond will not 
22

be very strong due to a lack of macrotexture. In some cases, shot blasting can be used to 

enhance macrotexture prior to HFST installation.

• Open graded asphalt surfaces. When applied to an open graded asphalt surface, a very thick and 

rigid layer of resin binder is created as the resin binder fills the voids in the pavement surface. 

This thick layer will have different thermal properties from the underlying asphalt layers and can 

lead to delamination of the open graded surface from underlying layers or substrate failure of 

the underlying layer. A best practice is to remove existing open graded asphalt surfaces and 

replace them with a conventional asphalt surface before applying HFST. 

• Replace pavement in poor condition prior to installing HFST to increase service life expectancy. 

Following recommendations, such as a 30-day cure period for new asphalt and concrete 

pavements prior to installing HFST, will increase the likelihood of a successful installation. 

3. Can patches that de-bond be fixed?

• This is not common but can be caused by an isolated spot on the pavement that was not 

cleaned well or had undetected solvent on the pavement. However, if small localized sections of 

HFST de-bond from the pavement, this can easily be repaired by milling back to a well-bonded 

area, cleaning the area well, and applying polymer resin and aggregate by hand to blend the 

patch in with the existing material. 

• More common is when a small section of pavement "pops out," but the HFST is still bonded to 

the fragment of pavement. If this is a limited occurrence, it does not indicate a catastrophic 

failure of the HFST and generally means the underlying pavement had a weak area and 

debonded from a lower layer of pavement. The pavement should be repaired and HFST 

reapplied if the area is large enough to cause roadway issues. If asphalt is used to patch the 

pavement, HFST should not be placed for at least 30 days. And if concrete is used, any curing 

compound should be removed and the surface cleaned before applying the HFST, since curing 

compounds act as bond breakers.

4. Will the polymer have a reaction with magnesium on a bridge deck?

No reactions have been found with magnesium chloride deicers. Some concrete repair materials may 

contain magnesium phosphate so it is important to consult the HFST resin binder manufacturer prior to 

the installation of any repair or patching material to confirm compatibility and installation requirements.

INSTALLATION

1. What surface preparation and installation conditions are important for successful 

installation?

General 

• All manufacturer installation instructions and specifications should be followed.
23

• Surface preparation is key for a successful HFST installation. Shotblasting for concrete and highpressure air wash for asphalt pavements should be done in advance of HFST application.

• Because HFST resin binders are thermosetting materials, temperature is a very important 

condition to consider for HFST installation. Temperature limitations for installation depend on

the type of polymer resin binder being used as well as the method for applying the aggregate. 

o A general rule of thumb is to not install HFST when the pavement surface temperature is 

below 50°F (or expected to fall below 50°F during installation) unless the resin binder 

system is formulated specifically for cooler temperatures. It is important to follow resin 

binder manufacturer recommendations for temperature restrictions. Also keep in mind 

that most resin binders cure slower in cooler temperatures, which will impact 

installation time. 

o As temperatures rise, the resin binder system will reach initial gel faster. Automated 

methods for aggregate application are often capable of fully covering the resin binder 

before it begins to gel at these higher temperatures. As ambient temperatures reach 

95°F and above, most resin binder systems will begin to thicken and gel within minutes. 

It is important to verify that the aggregate can be fully applied at the specified coverage 

rate before the resin binder begins to thicken. If the aggregate is not broadcast to the 

specified coverage rate while the resin binder is still in its liquid state, the application is 

at risk of only partial embedment of the aggregate. This can lead to early loss of 

aggregate in the wheel path and failure of the HFST system to provide the required 

friction values. Many agencies require a test section to determine that the method of 

aggregate application will be sufficient to install HFST at the required temperatures. It is 

important to follow agency specifications and the resin binder manufacturer’s 

instructions for the HFST application.

o Both surface and ambient temperatures are critical to a successful installation. If the 

aggregate can be applied to the resin binder immediately, HFST can be installed at 

temperatures exceeding 100°F (depending on manufacturer recommendations) as long 

as the resin binder has enough time to penetrate the pavement surface prior to 

reaching initial gel. Hence, continuous automated installation is the preferred method. 

• It is generally not practical or necessary to remove small oil spots, but very large or heavily 

saturated oil spots may need to be removed by aggressive washing with approved detergents 

and rinsing with clean water. These deposits are more common at intersection locations where 

vehicles tend to sit on the pavement at the intersection approach. When washing techniques 

are used, proper drying time and/or drying techniques should be considered. In some instances, 

heavily contaminated pavement should be removed and replaced.

• There should be no visible moisture present on the pavement surface at the time of the resin 

binder application. Compressed air may be used to help dry and remove moisture from pores in 

the pavement surface. A surface moisture test consisting of a plastic sheet taped in place on the 
24

pavement surface for a minimum of 2 hours, in accordance with ASTM D 4263, may be used to 

verify if the surface is dry enough for HFST application if there is any question. Use of this testing 

specification is not required by Federal law or regulation.

• Utilities, drainage structures, curbs, active joints, and any other structure within or adjacent to 

the treatment location should be protected against the application of the surface treatment 

materials. Existing pavement markings to be preserved adjacent to the application surface 

should be masked or care taken that the binder does not cover the markings. High-tack adhesive 

tape can be used to outline the perimeter of the application area, cover pavement markings, or 

to protect joints, etc. 

• Pavement markings that are not covered or consist of material other than paint should be 

removed. HFST will not fully adhere to thermoplastic road markings. The removal method may 

be grinding, light milling, shotblasting, or water blasting after which the surface should be dried 

and swept clean prior to HFST application. Pavement marking lines should be considered clean 

when the pavement has exposed aggregate showing through the existing marking. Care should

be taken to not damage or gouge the pavement surface when removing pavement markings. 

Uneven surfaces should not be repaired with the HFST system. 

• Pavement cracks greater than 1/4 inch in width and depth should be sealed 30 days prior to 

HFST installation if rubberized asphalt or similar products are used. Several manufacturers offer 

crack sealing materials that are compatible with HFST resin binder and may eliminate the 30-day 

cure period. When sealing cracks, it is important to ensure the sealant is recessed slightly below 

the pavement surface and not overbanded onto the pavement. Most agencies specify that joints 

and cracks less than 1/4 inch be pre-treated with the mixed polymer resin just prior to HFST 

placement. Once the polymer in the pre-treated areas has gelled, the HFST binder and 

aggregate topping installation may proceed.

o Repair all pavement defects such as spalls, potholes, raveling, and rutting prior to 

placing HFST. Consult the binder resin manufacturer to ensure compatibility of repair 

materials with the HFST system. Clean and fill all inadequately sealed joints, including 

shoulder areas within the treatment area. HFST may be applied over pavements 

exhibiting minor rutting or heaving; however, it should not be used as a repair for these 

conditions (e.g., to fill ruts). Proper evaluation of pavement condition during the project 

selection and design stage is important before considering HFST.

Concrete Surfaces

• HFST should not be applied to portland cement concrete that has been in place less than 30 

days. Concrete surfaces should be abrasively cleaned by shot blasting to remove oils, dirt, 

rubber deposits, curing compounds, paint carbonation, laitance, weak surface mortar, and other 

potentially detrimental contaminants that may interfere with the bonding or curing of the HFST. 

Shotblasting should achieve an International Concrete Repair Institute concrete surface profile 
25

(CSP) of 5. Shotblasting should always be followed with a high-pressure compressed air wash to 

remove any latent dust from the shotblasting process. 

• When using rapid strength concrete to shorten the 30-day waiting period prior to HFST 

installation, it is critical to qualify compatibility of the patching materials/rapid strength mortars 

with the HFST polymer resin binder as some patching materials may not provide a good bonding 

surface. No matter what material goes on top, installers should always refer to the 

manufacturer’s installation instructions to determine if it qualifies as compatible with the repair 

material. 

Asphalt Surfaces

• Before placement of HFST on an asphalt surface, the entire surface should be cleaned using a 

high-pressure air washing or other approved washing methods to remove oils, dirt, rubber 

deposits, paint, laitance, and other potentially detrimental contaminants that may interfere with 

the bonding or curing of the HFST. Acceptable cleaning should result in a surface with no oil 

spots, dirt, or other debris. Asphalt deposits larger than one inch in diameter and smaller areas 

spaced less than six inches apart should be removed.

• For applications on new asphalt pavements, it is recommended to wait a minimum of 30 days 

after paving before installing HFST. Asphalt pavements that still appear to be "tacky" or look wet 

on the surface should be evaluated for possible extension to the waiting period prior to 

installing the HFST. On open-graded friction course asphalt surfaces, stone mastic asphalt, or

pavement that has been treated with prior surface treatments (e.g., microsurfacing, slurry seal, 

etc.), contact the resin binder manufacturer for more information. 

• Several agencies have experimented with pressure washing or lightly shotblasting new asphalt 

surfaces to shorten the 30-day waiting period. This practice is not recommended since the 

potential for trapping moisture or volatile oils can still be a risk and can contribute to the failure 

of the HFST installation.

2. Can you apply HFST over existing striping?

• In general, HFST can be applied over painted lines, but thermoplastic lines should be removed 

prior to HFST installation. If the existing pavement markings are in good condition, it is 

recommended that the markings be retained by masking them off prior to HFST placement. 

Refer to resin binder manufacturer recommendations before applying over any surface 

treatment like paint lines.

3. Is installation over an open-graded friction courses (OGFC) an issue?

• While there have been many successful applications of HFST on OGFC, it is not recommended 

practice. OGFCs are relatively thin and the bond with underlying asphalt layers can be a highly 

variable. This has led to a few problematic installations since it is often difficult to detect 
26

underlying pavement issues. Recommended practice is to remove OGFC within the limits to be 

treated with HFST and place conventional asphalt pavement prior to HFST. 

• Successful installations over OGFC have used a double layer treatment to seal the voids with the 

first layer and use the top course to maintain the proper binder depth, which is necessary for 

the aggregate embedment into the HFST riding surface. However, the following precautions 

should be considered for placing a double layer HFST:

• Since a double layer is less flexible than a single layer, a sound pavement is most 

important. A double layer creates a thick layer of resin binder which is much less flexible 

than a single layer system and the underlying pavement (asphalt in particular). This 

thicker layer can increase shear forces at the bond interface due to differing thermal 

properties, leading to delamination (of the HFST or OGFC) or substrate failure. 

• Resin binder demand, or the application rate required to achieve proper aggregate 

embedment will likely be different for the second layer than the first, depending on the 

texture of the existing pavement surface. 

• A double-layer HFST is also less permeable than a single layer system, which increases 

vapor pressure between the HFST and underlying pavement, increasing the potential for 

stripping of underlying bituminous pavement surfaces.

• Additionally, if placing HFST over OGFC, the shoulder on the high side of the superelevation may 

need to be sealed to keep water from running through the OGFC and under the HFST, which can 

cause failure. It may also be necessary to extend the HFST further when the curve is on a grade 

in order to seal the OGFC to prevent water from running down the grade and under the HFST as 

well. Be aware that this adds to the quantity of HFST required.
27

4. What are some of the key factors that can affect the placement of HFST?

• Current methods of installing HFST vary based on recent advancements and the automation of 

mixing and placement equipment. Although some agencies still allow hand mixing and 

placement for HFST, the opportunities for human error with these methods are significant and 

warrant stringent quality control procedures within a specification to ensure consistent and 

proper application. The selection of different methodologies depends on the size of the 

installation, site-specific conditions like storage and ready access, and the availability of 

acceptable detour routes or traffic restrictions. 

• Because the HFST system will have a greater coefficient of thermal expansion than the 

pavement substrate, applying an even and consistent wet mil thickness for the resin binder is 

critical to the longevity of the system. Variable thickness within the HFST installation can 

increase the potential for cracking and spalling, especially when installed on pavements that 

show signs of degradation.

• Consistent mil thickness of the HFST is also important for maintaining even contact with vehicle 

tires. Any high spots that are created because of un-even installation practices can create "point 

loading" under traffic over the HFST system. These high spots can potentially transfer very high 

dynamic impact to the underlying pavement potentially leading to early age spalling and 

delamination of the HFST.

• Prompt application of aggregate onto the resin binder is important to ensure proper 

embedment of the aggregate within the resin binder. At higher temperatures, resin binder 

systems tend to reach initial gel within minutes. When the binder gels, the viscosity increases 

which can inhibit aggregate penetration and proper embedment. This can result in premature 

loss of surface aggregates.

5. What is the difference between manual and fully automated HFST installation?

• There are two main methods for installing HFST: manual and fully automated. The preferred 

application method depends on the size of the project, the number of installations within the 

contract, and specific project needs. For example, manual installation may be used for small 

spot-treatments or irregular areas where a fully automated process is not practical, while a fully 

automated process might be used for larger contracts consisting of numerous sites. Most 

agencies contract out their HFST installations to avoid purchasing HFST-specific equipment. 

Regardless of the method used for installation, robust specifications and good inspection 

practices are essential for a proper installation, but particularly for manual installation where 

there are more opportunities for human error. 

o Manual – Manual HFST application is ideal for small spot locations of 200 SY or less 

where it may be difficult or not economical to bring in automated installation 

equipment. For a completely manual application, the resin binder components and any 

additives are manually proportioned and mixed on site in a large mixing vessel. The 
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mixed resin binder is poured onto the prepared surface and spread to the proper mil 

thickness using notched squeegees. Next, the aggregate is broadcast on top of the resin 

binder. There is no preferred method to broadcast the aggregate, but the binder should

be completely covered (i.e., until refusal). While the manual application method is ideal 

for keeping costs low on small projects, this method has a few drawbacks. Given the 

opportunity for human error and inconsistency in all aspects of application 

(proportioning, mixing, and placing resin binder and application of aggregate), quality 

and uniformity of manually applied treatments are a concern. Manual application is a 

much slower process and working under live traffic conditions increases safety risks by 

prolonging workers’ exposure to traffic. In addition, the prolonged presence of a work 

zone can potentially cause secondary crashes. While there are several mechanicallyassisted methods for resin binder proportioning and mixing and aggregate application 

which may help reduce human error, these devices generally do not improve resin 

binder application and may only marginally decrease application time.

o Fully Automated – A fully automated HFST application typically involves a truck that is 

customized to condition, meter, and mechanically blend the resin binder components in 

accordance with manufacturer guidelines based on the current ambient or surface 

temperature. These machines are capable of applying a consistent and uniform wet mil 

thickness of the resin binder to the proper application rate, followed immediately by a 

uniform layer of aggregate, without any manual squeegeeing or spreading. The truck 

contains the binder and aggregate in large bulk containers on its chassis. The application 

can be customized to the intended lane width of the treatment. The fully automated 

method minimizes lane closures due to quick installation time and reduces the number 

of workers on the roadway. The installation speed and the uniformity of application of 

binder and aggregate reduces the risk of premature failure and improves the likelihood 

of a higher quality application. This method may reduce overall cost on large projects or 

projects bundled from numerous small installations.

6. Can agency personnel install HFST?

Yes, but agency personnel should receive proper training before attempting an installation, and a trial 

project or test strip is highly recommended if the installation crew does not have prior experience. Due 

to the cost of investment in automated application equipment, agency personnel will typically use 

manual installation methods. As such, this should be limited to small or isolated applications only.
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FHWA-SA-22-016

7. What are items to look for in terms of early-age performance that may indicate materials 

and workmanship issues?

• Uncured resin binder. This will normally appear as a discolored area where the HFST is soft and 

is typically caused by improper or incomplete blending of the resin binder components. These 

areas will not retain aggregate under traffic wear and should be removed and patched.

• Aggregate loss. HFST will normally shed aggregate over the first 24-72 hours after opening to 

traffic. This aggregate will accumulate along the edge of the lane or out in the shoulder or 

adjacent lane and should be removed through re-sweeping. If significant aggregate loss 

continues, the cause should be further investigated. 

• Delamination. This generally manifests as “sheets” of HFST peeling away from the underlying 

pavement and may be caused by improper surface preparation. Sounding techniques can be 

used to identify the extent of delamination. These areas should be patched. 

• Aggregate polishing. Polishing will cause the surface to have a smooth or glassy appearance 

under traffic wear. Calcined bauxite aggregate should not polish and therefore any polishing 

should be investigated further. 

• Discoloration. This will appear as a visible difference in color of localized areas, and may be an 

indicator of moisture trapped beneath the HFST. It does not necessarily indicate a problem with 

the HFST but should be monitored over time.

• Surface wear loss of HFST. This is a condition when the HFST wears off, exposing the underlying 

pavement. It generally begins with loss of aggregate, which exposes the resin binder which is 

quickly worn off by traffic. It is an indicator that the HFST resin binder was placed too thin, 

aggregate was applied after gelling occurred, or the resin binder was not strong enough to 

retain the aggregate, and will call for the reapplication of HFST.

• Friction loss. Friction loss is identified through routine measurement of HFST friction. A 

sustained decrease in friction indicates a problem with the aggregates (e.g., polishing) or the 

HFST system. 

• Failure of underlying pavement. This generally manifests as potholes in the HFST surface where 

both the HFST and underlying pavement break away under traffic and is more common with 

asphalt pavement. It generally indicates a cohesive failure within a weak asphalt layer or 

stripping of the asphalt due to moisture. Isolated areas can be patched but if deterioration 

progresses, removal and replacement should be undertaken. 

For additional information, please contact:

Joe Cheung, P.E.

High Friction Surface Treatment Lead

FHWA Office of Safety

joseph.cheung@dot.gov

Tori Brinkly, P.E.

Senior Safety Engineer

FHWA Resource Center

tori.brinkly@dot.gov