HIGH FRICTION SURFACE TREATMENT 

SITE SELECTION AND

INSTALLATION GUIDE
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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NOTICE

This document is disseminated under the sponsorship of the U.S. Department of 

Transportation in the interest of information exchange. The U.S. Government assumes no 

liability for the use of the information contained in this document.

The U.S. Government does not endorse products or manufacturers. Trademarks or 

manufacturers’ names appear in this report only because they are considered essential to the 

objective of the document.

QUALITY ASSURANCE STATEMENT

The Federal Highway Administration (FHWA) provides high-quality information to serve 

Government, industry, and the public in a manner that promotes public understanding. 

Standards and policies are used to ensure and maximize the quality, objectivity, utility, and 

integrity of its information. FHWA periodically reviews quality issues and adjusts its programs 

and processes to ensure continuous quality improvement. 

NON-BINDING CONTENTS

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. While this is non-binding 

guidance, you must comply with the applicable statutes or regulations.
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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TECHNICAL DOCUMENTATION PAGE

1. Report No.

FHWA-SA-21-093

2. Government Accession 

No.

3. Recipient's Catalog No.

 

4. Title and Subtitle

High Friction Surface Treatment Site Selection and Installation Guide

5. Report Date

October 2021 

6. Performing Organization Code 

7.Author(s) 

David Merritt, Scott Himes, and R.J. Porter 

8. Performing Organization Report No.

9. Performing Organization Name and Address

Vanasse Hangen Brustlin, Inc (VHB)

8300 Boone Blvd., Suite 700

Vienna, VA 22182-2626 

10. Work Unit No.

11. Contract or Grant No.

DTFH61-05-D-00024 (VHB)

12. Sponsoring Agency Name and Address

Federal Highway Administration Office of Safety 

1200 New Jersey Ave., SE

Washington, DC 20590

13. Type of Report and Period

Draft Report, September 2020 – 

October 2021

14. Sponsoring Agency Code

FHWA

15. Supplementary Notes

The contract manager for this report was Joseph Cheung. 

16. Abstract

This Guide provides an update to the 2016 High Friction Surface Treatment (HFST) Curve Selection and Installation Guide 

based on current practices for HFST deployment. HFST, when installed properly, can reduce both wet and dry frictionrelated crashes. While the 2016 HFST Guide focused on application of HFST on curves, this Guide also discusses HFST 

for ramps, intersections, and other applications, and summarizes best practices agencies have used for installing HFST. 

Other key additions include updated recommendations on practices for HFST applications, site selection, installation, and 

performance monitoring. This Guide also targets agencies who are considering implementing HFST as a safety 

countermeasure for the first time and includes a stand-alone inspection guide that agencies can use to establish inspection 

protocols for HFST installation. 

17. Key Words: 

High friction surface treatments, curves, 

intersections, ramps, safety, pavement friction 

18. Distribution Statement

No restrictions.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this 

page) Unclassified

21. No. of Pages

 144 

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed pages authorized 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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TABLE OF CONTENTS

Executive Summary...................................................................................... 1

Chapter 1—Overview................................................................................... 3

1.1 What is High Friction Surface Treatment?......................................................................................4

1.2 HFST Benefits and Effectiveness........................................................................................................6

1.3 Steps for HFST Development......................................................................................................... 10

1.4 Purpose and Structure of the Guide ............................................................................................. 10

Chapter 2—Identification of HFST Candidate Locations ...................... 13

2.1 Site-specific Safety Approach .......................................................................................................... 15

2.2 Systemic Approach............................................................................................................................ 20

2.3 Pavement Friction.............................................................................................................................. 24

2.4 Speed Differentials For Curves....................................................................................................... 28

2.5 Roadway Geometry .......................................................................................................................... 29

Chapter 3—Field Verification and Design................................................ 31

3.1 Field Verification ................................................................................................................................ 31

3.2 Design ................................................................................................................................................... 34

Chapter 4—HFST Materials ...................................................................... 39

4.1 Aggregate............................................................................................................................................. 39

4.2 Resin Binder........................................................................................................................................ 43

Chapter 5—Specifications and Installation.............................................. 47

5.1 Key Components of HFST installation.......................................................................................... 47

5.2 HFST Specifications........................................................................................................................... 48

5.3 Application Methods......................................................................................................................... 58

5.4 Special Circumstances and Considerations................................................................................. 63

Chapter 6—HFST Inspection Guide......................................................... 65

6.1 Overview of HFST............................................................................................................................. 65

6.2 Pre-Construction............................................................................................................................... 66

6.3 HFST Materials Inspection............................................................................................................... 66

6.4 Surface Preparation Inspection....................................................................................................... 67

6.5 HFST Application Inspection........................................................................................................... 72

6.6 Inspection of Aggregate Removal................................................................................................... 78

6.7 Inspection of Finished Surface......................................................................................................... 81

6.8 Acceptance Testing ........................................................................................................................... 82

6.9 Early-Age Monitoring ........................................................................................................................ 83

6.10Inspection Checklist......................................................................................................................... 88
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Chapter 7—Performance Monitoring and Replacement ....................... 89

7.1 Causes of HFST Failure .................................................................................................................... 89

7.2 Performance monitoring .................................................................................................................. 93

7.3 Removal and Replacement............................................................................................................... 99

Chapter 8—Cost Estimation and Funding ............................................. 101

8.1 HFST Cost......................................................................................................................................... 101

8.2 B/C Ratios.......................................................................................................................................... 102

8.3 Funding ............................................................................................................................................... 103

Chapter 9—Conclusion ............................................................................ 105

Chapter 10—Additional Resources......................................................... 107

Appendix A: Other Potential HFST Applications................................. 110

HFST as an Alternative to Geometric Modifications..................................................................... 110

HFST as an Alternative to Increased Roadside Clear Zones....................................................... 111

HFST for Tangent Applications........................................................................................................... 111

HFST for Tunnels................................................................................................................................... 111

HFST for Steep Grades......................................................................................................................... 112

Colored Surfaces.................................................................................................................................... 113

Steel Plate Trench Covers.................................................................................................................... 118

Appendix B: Examples of Systemic Deployment of HFST .................. 119

Louisiana . ................................................................................................................................................. 119

Georgia ... ................................................................................................................................................. 119

Thurston County.................................................................................................................................... 120

Delaware ................................................................................................................................................. 120

Appendix C: HFST Inspection Checklist............................................... 121

References ................................................................................................. 125
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LIST OF TABLES

Table 1. Examples of crash reduction for HFST from States with mature programs.......................7

Table 2. Aggregate CMF results for HFST curve sites from three States: PA, KY, and WV 

(Merritt, 2020b, Lyon, 2020)..........................................................................................................................8

Table 3. CMF results for HFST ramp sites from KY and AR (Merritt et al. 2020, Lyon et al. 

2020)....................................................................................................................................................................8

Table 4. Modified design policy for use of HFST (“HFS”) in the United Kingdom based on 

roadway and traffic characteristics (Highways England 2020)............................................................. 14

Table 5. PennDOT guidelines for HFST usage on asphalt pavements............................................... 32

Table 6. PennDOT guidelines for HFST usage on concrete pavements. .......................................... 32

Table 7. Recommended distance upstream of curve PC to begin HFST application (Brimley and 

Carlson 2012). ................................................................................................................................................ 34

Table 8. Virginia DOT resin binder application rate adjustment based on pavement 

macrotexture.................................................................................................................................................. 37

Table 9. Resin binder product label showing minimum curing time based on temperature........ 45

Table 10. Physical property requirements for HFST resin binder materials.................................... 49

Table 11. Physical property requirements for HFST aggregate materials. ....................................... 50

Table 12. Key advantages and disadvantages of application methods................................................ 63

Table 13. Safety Performance Evaluation Methods................................................................................ 94

Table 14. Long-term friction performance of HFST.............................................................................. 97

 
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LIST OF FIGURES

Figure 1. Photograph. Example of HFST installation (Merritt et al. 2020a).........................................4

Figure 2. Photograph. HFST placed over a conventional asphalt pavement surface (Merritt et al. 

2020a). ................................................................................................................................................................. 4

Figure 3. Graphic. Relationship between speed, friction demand, and friction supply (AASHTO 

2008). ................................................................................................................................................................ 25

Figure 4. Graphic. Increase in speed differential (Pratt et al. 2014)................................................... 28

Figure 5. Graphic. Illustration of pavement microtexture and macrotexture. ................................ 40

Figure 6. Photograph. Calcined bauxite aggregate for HFST. .............................................................. 41

Figure 7. Graph. Micro-Deval loss from testing of calcined bauxite and other reference 

aggregates (Wilson and Mukhopadhyay 2016)........................................................................................ 42

Figure 8. Graph. Impact of pavement temperature and resin binder viscosity on resin binder film 

thickness due to drain down (Wilson and Mukhopadhyay 2016). ..................................................... 44

Figure 9. Graphic. Illustration of aggregate embedment in resin binder layer (FDOT 2021). ..... 53

Figure 10. Equation. Calculation of coverage rate in gallons per square yard based on mil 

thickness. ......................................................................................................................................................... 54

Figure 11. Equation. Calculation of coverage rate as SY per gallon based on mil thickness........ 54

Figure 12. Photograph. Example of a uniform application of aggregate with no resin binder 

visible. ............................................................................................................................................................... 54

Figure 13. Photograph. Example of mechanically-assisted manual resin binder application. ........ 59

Figure 14. Photograph. Example of manual application of aggregate, broadcast by hand. ............ 60

Figure 15. Photograph. Example of mechanically-assisted manual aggregate application using a 

venturi blower................................................................................................................................................ 60

Figure 16. Photograph. Example of a fully-automated installation vehicle. ....................................... 61

Figure 17. Photograph. Example of resin binder and aggregate placement on a fully-automated 

installation vehicle.......................................................................................................................................... 62

Figure 18. Photograph. HFST placed over a conventional asphalt pavement surface (Merritt et 

al. 2020a).......................................................................................................................................................... 65

Figure 19. Photo. Example of bituminous crack sealant in asphalt pavement recessed from the 

top surface of the pavement. ...................................................................................................................... 68

Figure 20. Photo. Example of compressed air wash surface preparation. ........................................ 69

Figure 21. Photo. Shotblast surface preparation showing overlap between successive passes. .. 69

Figure 22. Photo. Shotblast concrete surface with CSP = 5................................................................ 70
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Figure 23. Photo. Example of pavement striping removal using milling which has not damaged 

the underlying pavement.............................................................................................................................. 71

Figure 24. Photo. Example of masking of drainage structures near HFST application................... 71

Figure 25. Photo. Wet film thickness gage used to measure resin binder thickness during 

application........................................................................................................................................................ 73

Figure 26. Photo. Typical tools and equipment for resin binder proportioning and mixing for 

manual application. ........................................................................................................................................ 74

Figure 27. Photo. Example of spiked shoes worn by squeegee operator......................................... 75

Figure 28. Photo. Notched rubber squeegee for spreading resin binder during manual 

application........................................................................................................................................................ 75

Figure 29. Photo. Example of manual resin binder application............................................................ 76

Figure 30. Photo. Example of manual application of HFST aggregate................................................ 77

Figure 31. Photo. Example of fully automated resin binder application followed by automated 

aggregate application demonstrating uniformity of coverage. ............................................................. 78

Figure 32. Photo. Example of aggregate removal using a power broom........................................... 79

Figure 33. Photo. Example of aggregate removal using a vacuum truck. .......................................... 79

Figure 34. Photo. Example of exposure of underlying pavement after sweeping. .......................... 80

Figure 35. Photo. Example of loose aggregate migration onto adjacent lanes and shoulders...... 81

Figure 36. Photo. Example of discoloration indicating uncured resin binder................................... 82

Figure 37. Photo. Example of areas where HFST is missing and will require repair...................... 82

Figure 38. Photo. Example of aggregate shedding and accumulation along lane edge and on 

paved shoulder. .............................................................................................................................................. 84

Figure 39. Photo. Example of delamination of HFST from underlying pavement surface. ............ 85

Figure 40. Photo. Example of polished HFST surface in wheelpaths. ................................................ 86

Figure 41. Photo. Example of HFST discoloration likely caused by moisture.................................. 86

Figure 42. Photo. Example of HFST worn off in the wheelpaths........................................................ 87

Figure 43. Photo. Example of failure of underlying pavement leading to isolated failures 

(potholes) of HFST........................................................................................................................................ 88

Figure 44. Photograph. Example of localized failures due to poor binder mixing (FDOT 2021). 89

Figure 45. Photograph. Example of soft areas in resin binder shortly after construction (FDOT 

2021). ................................................................................................................................................................ 90

Figure 46. Photograph. Example exposure of underlying pavement due to inadequate resin 

binder thickness. ............................................................................................................................................ 90
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Figure 47. Photograph. HFST with inadequate aggregate coverage due to delayed aggregate 

application........................................................................................................................................................ 91

Figure 48. Photo. Example of an area of HFST delamination from the underlying pavement 

surface. ............................................................................................................................................................. 92

Figure 49. Photograph. Example failure of underlying pavement (delamination of surface layer) 

resulting in failure of HFST.......................................................................................................................... 92

Figure 50. Graphic. Cohesive failure of underlying pavement (Waters 2011)................................. 93

Figure 51. Photograph. Example of cracking in underlying pavement reflecting through HFST. . 98

Figure 52. Photograph. Example of aggregate loss under traffic wear............................................... 99

Figure 53. Graphic. Approximate breakdown of HFST cost (Atkinson et al. 2016).................... 101

Figure 54. Photograph. Example of HFST as an alternative to curve realignment (FHWA 2015).

......................................................................................................................................................................... 110

Figure 55. Photograph. Example of HFST used for tunnel application. ........................................... 112

Figure 56. Photograph. Example of light reflectance off of a light-colored HFST tunnel. ........... 112

Figure 57. Photograph. HFST application for steep grade at intersection approach (FHWA 

2016). .............................................................................................................................................................. 113

Figure 58. Photograph. Lane demarcation with two colors of polymer overlay........................... 114

Figure 59. Photograph. Example of HFST used for demarcation at an intersection approach. . 114

Figure 60. Photograph. Example of HFST used for bus lane demarcation. .................................... 115

Figure 61. Photograph. Example of HFST used for pedestrian crossing. ........................................ 115

Figure 62. Photograph. Example of HFST used for roundabout demarcation............................... 116

Figure 63. Photograph. Green bicycle lane application. ...................................................................... 116

Figure 64. Photograph. Railroad crossing application.......................................................................... 117

Figure 65. Photograph. Manual application of HFST to bridge deck................................................ 117

Figure 66. Photograph. HFST with calcined bauxite on steel trench plates (Heaton 

Manufacturing n.d.). ..................................................................................................................................... 118
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ACRONYMS

AADT annual average daily traffic

AASHTO American Association of State Highway and Transportation Officials 

AR Arkansas 

ATSSA American Traffic Safety Services Association

BBI ball-bank indicator 

B/C benefit-cost

CMF crash modification factor 

CPFM continuous pavement friction measurement

CTE coefficient of thermal expansion

DFT dynamic friction tester

DOT department of transportation

DOTD Department of Transportation and Development 

EB empirical Bayes 

EEC excess expected crashes 

FHWA Federal Highway Administration

FDOT Florida Department of Transportation 

FL Florida 

HFST high friction surface treatment 

HFT highway friction tester

HSIP Highway Safety Improvement Program 

HSM Highway Safety Manual

HOSSOD head-on sideswipe opposite direction

IL investigatory level

KABCO Injury Scale established by the National Safety Council

KY Kentucky 

KYTC Kentucky Transportation Cabinet 

LWST locked-wheel skid tester

MDA Micro-Deval Apparatus

MMA methyl methacrylate
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MPD mean profile depth

mph miles per hour 

MTD mean texture depth

NTPEP National Transportation Product Evaluation Program

NZTA New Zealand Transport Agency

OGFC open graded friction course

PA Pennsylvania 

PC point of curvature

PDO property damage only

PennDOT Pennsylvania Department of Transportation 

PFMP pavement friction management program

PSV polished stone value

PT point of tangency

QCP quality control plan

QPL qualified product list

RwDSIP Roadway Departure Safety Implementation Plan

ROR run-off-road

RSA road safety audit 

RTM regression-to-the-mean

RwD roadway departure 

SPF safety performance function 

SSA safe system approach 

TCMS Texas curve margin of safety

TTI Texas Transportation Institute 

usRAP U.S. Road Assessment Program 

ViDA Vehicle Information and Diagnostics for Aftersales 

WV West Virginia
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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EXECUTIVE SUMMARY

The purpose of this Guide is to update and expand on the information provided in FHWA’s 

2016 High Friction Surface Treatment Curve Selection and Installation Guide. Over the past 

five years since that Guide was published, the use of HFST has increased dramatically in the 

U.S., and practices for site selection, materials, installation, and performance monitoring have 

evolved. While the 2016 Guide focused on HFST for curve applications, this Guide provides 

information on other applications such as ramps and intersections where pedestrians are most 

likely to cross the roadway, even though curves remain the predominant application for HFST.

The content of this Guide is based on successful practices and lessons learned from a number 

of agencies with mature HFST programs that have deployed HFST on a large scale. While some 

agencies maintain internal guidance for HFST deployment, there are few resources summarizing 

noteworthy practices that agencies without this form of guidance can use. This document does 

not seek to prescribe certain practices, but rather highlights those that have been successful. 

This Guide is intended to assist agencies seeking to implement HFST as a safety 

countermeasure for the first time, to help agencies with limited deployment to expand and 

improve their program, and to help agencies with mature programs to further refine their 

program. Key topics for HFST deployment covered in this document include:

• Site Selection—Discussion of how to determine where to deploy HFST to address 

friction-related crashes. This includes guidance on site-specific (crash-history) site 

selection as well as systemic deployment. The Guide also highlights tools for data-driven 

approaches for site selection. 

• Field Verification and Design—Information on how to verify if locations identified 

from the site selection process are appropriate for HFST deployment and guidance on 

factors that may be considered in a project design. 

• Materials and Specifications—Summary of key properties for HFST resin binder and 

aggregate materials and guidance on specifications based on successful practices. 

• Installation and Inspection—Discussion of the importance of proper installation 

practices and inspection of HFST placement for ensuring long-term performance to 

achieve the desired benefit/cost (B/C) ratio. Chapter 6 provides a stand-alone guidance 

document for installation inspection, complemented with an inspection checklist 

(Appendix C) and downloadable pocket guide.

• Performance Monitoring—Explores considerations for performance monitoring 

with respect to both safety performance and functional (friction and durability) 

performance. 

HFST is a highly effective and mature safety countermeasure for reducing both wet and dry 

pavement friction-related crashes. When applied at appropriately selected locations and 

installed properly, exceptional B/C ratios have been realized by many agencies in the U.S. It is 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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the intent of this Guide to help further improve HFST deployment practices in the U.S. to help 

agencies realize the benefits of this safety countermeasure. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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CHAPTER 1—OVERVIEW

In 2019, there were approximately 6.76 million crashes reported in the U.S., accounting for

36,096 fatalities and over 2.74 million injuries (National Center for Statistics and Analysis 2020). 

Half of the 2019 fatalities were the result of roadway departure (RwD) crashes and more than 

23 percent were intersection-related (NHTSA 2021).

Often, a small subset of the total highway network is responsible for a significant percentage of 

certain crash types. Roughly 25 percent of fatal crashes are associated with horizontal curves, 

yet horizontal curves make up only 5 percent of our Nation’s roadways (FHWA 2016). And 

approximately 76 percent of curve-related fatal crashes are the result of roadway departure 

(Torbic et al. 2004). Intersections, likewise, make up a very small percentage of the total 

highway network. 

Pavement friction plays a major role not only in stopping distance but also in helping keep 

vehicles in their lane. Agencies have identified pavement condition as one of the major 

contributing factors in RwD and intersection crashes. The level of pavement friction is reduced 

when a pavement surface is wet or polished from wear, which may lead to skidding or 

hydroplaning. 

Vehicles have different friction demands depending on the characteristics of the roadway. For 

example, a vehicle traversing a horizontal curve requires a greater level of friction than vehicles 

on a tangent section, and furthermore, large trucks require a greater level of friction to 

traverse a curve than passenger vehicles. Common locations that require higher friction values 

are horizontal curves, ramps, steep grades, or intersection approaches. As a result of the 

increased friction demand, the roadway surface at these locations often becomes prematurely 

polished, reducing the pavement friction and contributing to higher crash rates. Excessive 

speeds or distracted driving can also contribute to the crash rates in areas where friction 

demand is high. 

A high friction surface treatment (HFST) is a low-cost safety countermeasure used specifically 

for these purposes. HFST significantly increases pavement friction to help prevent drivers from 

losing control and decrease stopping distance when at least one of the following conditions 

exist (Atkinson et al. 2016): 

• Vehicle friction demand exceeds available pavement friction. 

• Vehicles are traveling too fast for the geometric design of a curve. 

• Vehicles are traveling too fast for roadway conditions (e.g., wet or icy pavement). 

• Pavement surface has been polished from wear.
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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1.1 WHAT IS HIGH FRICTION SURFACE TREATMENT? 

HFST is a safety and pavement surface treatment that dramatically and immediately increases 

pavement friction to reduce crashes, injuries, and fatalities associated with friction demand 

issues. The treatment 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 can also restore pavement surface friction where 

traffic has polished existing pavement surface aggregates. 

HFST is installed by spreading a thin layer of polymeric resin binder (typically epoxy or 

polyester) over the pavement surface, then broadcasting or dropping a 1- to 3-mm abrasionand polish-resistant aggregate (typically calcined bauxite) onto the resin layer (figure 1). The 

resin binder bonds the aggregate to the pavement surface, leaving a thin, superficial, pavement 

surface treatment (figure 2) that can be applied during a short closure of the roadway. 

© The Transtec Group 

Figure 1. Photograph. Example of HFST installation (Merritt et al. 2020a). 

© The Transtec Group 

Figure 2. Photograph. HFST placed over a conventional asphalt pavement surface 

(Merritt et al. 2020a). 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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HFST is not 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. 

HFST as described herein is also different from thin-polymer bridge deck overlays. While the 

polymeric resin binder and installation methods used for polymer bridge deck overlays are 

similar to that used for HFST, bridge deck overlays are designed to help seal and preserve the 

bridge deck while also enhancing surface friction. As such, agencies typically use different 

aggregate materials for bridge deck overlays. 

The use of HFST as a safety countermeasure in the United States has grown exponentially over 

the past 15 years. As of 2005, there were only one or two known HFST demonstration 

installations on curves or ramps in the United States, and by 2021, at least 44 States had at least 

one (1) HFST installation, with 10 states reporting over 100 installations, 5 states reporting 50-

100 installations, 15 states reporting 10-50 installations, and the remaining states reporting one 

to ten installations. This accounts for millions of SY of HFST installed in just over 15 years. A 

State DOT HFST Status map and additional resources on HFST can be found at the following 

website: https://safety.fhwa.dot.gov/roadway_dept/pavement_friction/high_friction/. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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1.2 HFST BENEFITS AND EFFECTIVENESS

HFST is a unique low-cost safety countermeasure because 

it is specifically intended to dramatically increase 

pavement friction for the purpose of reducing crashes. 

There are no other known pavement surface treatments 

that enhance pavement friction to the same level while 

sustaining this friction enhancement over time. When 

properly deployed, HFST can provide a dramatic crash 

reduction and substantial benefit-cost (B/C) ratio. This 

section describes some examples of safety effectiveness 

findings and lists the key advantages of HFST over other 

treatments. 

1.2.1 SAFETY BENEFITS AND EFFECTIVENESS

HFST effectiveness varies by location, but agencies have 

found that HFST can more than double or triple existing 

pavement friction, reduce stopping distance by 25 to 30 

percent, and provide crash reductions from 45 to 100 

percent (Atkinson et al. 2016). 

Table 1 provides examples of effectiveness for routine 

HFST deployment and summarizes estimated overall and 

wet crash reductions for three States with mature HFST 

programs. Note that while HFST is most effective in 

reducing wet pavement crashes, it is also effective in 

reducing dry pavement crashes, as evidenced by the 

dramatic reductions in total crashes. 

Marquette Interchange 

West-North Connector

Milwaukee, Wisconsin

Before HFST (3 year): 219 crashes

After HFST (3 year): 9 crashes

96% crash reduction

California Route 17, 

Laurel Road Curve

Northern California

Before HFST (3 year): 

156 crashes (141 wet)

After HFST (3 year): 8 (2 wet)

95% crash reduction

Examples of Crash 

Reduction from HFST 

Deployment

© Transtec 

© Transtec 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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Table 1. Examples of crash reduction for HFST from States with mature programs. 

State Site 

Information Total Crash Reduction Wet Crash Reduction

Pennsylvania 

(PA)1 47 curve treatments 70% 87%

Kentucky (KY)2 43 curves and ramp 

treatments

73% (curves)

78% (ramps)

86% (curves)

85% (ramps)

Florida (FL)3 “Tight curve” 

treatments

44% 84% 

1. Locations had 3 to 5 years of before-after crash data (PennDOT 2018).

2. Three years of crash data before installation and 1 to 4 years of crash date after installation (Von 

Quintus and Mergenmeier 2015).

3. Florida DOT 2021. 

While the estimated crash reductions presented thus far are based on naïve before and after 

evaluations, a Federal Highway Administration (FHWA) study developed crash modification 

factors (CMFs) for HFST using the empirical Bayes (EB) methodology for horizontal curve and 

ramp applications in four States: Pennsylvania (PA), Kentucky (KY), Arkansas (AR), and West 

Virginia (WV) (Merritt 2020b). A CMF is used to estimate the expected number of crashes at a 

location after installing a countermeasure. It is a multiplicative factor used to estimate future 

crash frequency from a base crash frequency. For example, if a site observes 10 crashes per 

year, and the CMF for a countermeasure is 0.80, then you would expect 8 crashes per year 

after countermeasure installation (10 x 0.80 = 8). The research developed CMFs for several 

crash types, including total, injury, run-off-road, wet-road, and head-on sideswipe opposite 

direction (HOSSOD) crashes. Table 2 and table 3 show the CMFs from this study, which 

provide a more statistically rigorous estimation of the crash-reduction benefits of HFST.
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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Table 2. Aggregate CMF results for HFST curve sites from three States: PA, KY, 

and WV (Merritt et al. 2020b, Lyon et al. 2020). 

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. 

Table 3. CMF results for HFST ramp sites from KY and AR (Merritt et al. 2020b, 

Lyon et al. 2020). 

Crashes after treatment application

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

Arkansas

Total 97 92.43 1.045 (0.125)

Injury 19 17.72 1.086 (0.281)

Run-off-road 3 3.64 0.788 (0.464)

Wet road 6 44.63 0.133 (0.055)

Kentucky

Total 183 860.44 0.212 (0.018)

Injury 46 125.13 0.365 (0.061)

Run-off-road 6 29.51 0.202 (0.084)

Wet road 49 621.07 0.079 (0.012)

Note: CMF = crash modification factor; EB = empirical Bayes; s.e. = standard error. CMFs that are 

statistically significant at the 5-percent level are indicated in boldface.
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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HFST is an important countermeasure for a Safe System Approach (SSA) to improving roadway 

safety. SSA is a “holistic view of the road system that first anticipates human mistakes and 

second keeps impact energy on the human body at tolerable levels” (FHWA 2020c). HFST can 

help compensate for human error when drivers improperly navigate curves, ramps, and 

intersection approaches. HFST supports the Safe System elements (i.e., Safe Speeds, Safe Roads, 

Safe Users) because it helps keep vehicles in their lane, reduces stopping distance, and thus can 

improve safety for all road users.

1.2.2 ADVANTAGES OF HFST

Some of the key advantages of HFST include: 

• Low-cost treatment—HFST is a low-cost, crash-reduction treatment capable of 

providing greater safety benefit than other low-cost safety measures such as advanced 

curve warning signs, advisory speed plaques, pavement markings, chevrons, and guardrail

when strategically placed at targeted locations. It is a substantially lower-cost alternative 

to more drastic safety improvements such as repaving, curve realignment, and other 

roadway geometry changes. 

• Minimal impact to traffic—HFST can generally be installed and opened to traffic 

within hours, minimizing lane closure time, and the associated impact on traffic

(including the potential for secondary crashes from prolonged construction work 

zones), particularly if a detour is required. It can generally be installed during nighttime 

lane closures (temperature permitting) and can be installed using single-lane closures, 

allowing traffic to remain on other lanes.

• Superficial treatment—HFST is a thin, superficial overlay of the existing pavement 

which will not change the pavement cross-slope and alter drainage, reduce overhead 

clearance, or require guardrails or barriers to be raised. 

• Quick implementation—Agencies can expect a relatively short planning process 

(with minimal construction drawings) and installation timeframe, compared to other 

alternatives. Some agencies have reported timeframes as short as 10 days for small 

applications or 6 months for larger projects from concept to completion. 

• Negligible environmental impacts—The treatment is only applied between existing 

pavement edges and does not require disturbances to the surrounding ground. This can 

result in shortened environmental review periods and lessen environmental mitigation.

• Durable and long lasting—HFST has demonstrated excellent long-term pavement 

surface functional durability. A properly installed HFST over a sound pavement surface 

should have a service life of at least 7 to 10 (or more) years, depending on the level of 

traffic exposure.
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1.3 STEPS FOR HFST DEVELOPMENT 

The following is a summary of the step-by-step process for HFST implementation as a safety 

countermeasure to reduce friction-related crashes. The various chapters of this Guide will 

cover key components of HFST implementation as follows:

The intent of this Guide is to assist agencies with HFST implementation for the first time or to 

help agencies with established HFST programs to further refine their program such that HFST 

becomes a routinely used safety countermeasure.

1.4 PURPOSE AND STRUCTURE OF THE GUIDE

The purpose of this Guide is to provide key information for HFST implementation as a safety 

countermeasure to reduce friction-related crashes. Each chapter provides information on the 

various steps of the implementation process as follows: 

• Chapter 2 provides information on HFST candidate site selection. It discusses both sitespecific and systemic approaches to site selection. This chapter also discusses the 

importance of considering pavement friction in the site selection process as well as 

other factors such as roadway geometry and speed differentials that may impact site 

selection. 

• Chapter 3 provides information on field verification and design for HFST candidates. 

Field verification includes an assessment of pavement condition and other potential 

factors that may be contributing to crashes. Design includes issues related to project 

scoping, such as identification of treatment limits, traffic control considerations, surface 

preparation requirements, and other factors that may affect project cost. 
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• Chapter 4 discusses HFST materials, namely the polymeric resin binder and aggregate 

materials that constitute an HFST. This chapter also discusses key properties and sitespecific considerations for these materials. 

• Chapter 5 provides information on HFST specifications and installation practices based 

on the current state-of-the-practice in the HFST industry. This includes key components 

for a robust HFST specification and key considerations for installation methods. 

• Chapter 6 is an Inspection Guide for HFST installation. This Inspection Guide, which is 

targeted towards project inspectors, provides an overview of the HFST installation 

process and key considerations for each aspect of the installation. The Inspection Guide 

will also serve as a standalone guide accessible via smart phone or tablet in the field for 

quick reference.

• Chapter 7 discusses the importance of performance monitoring and provides guidance 

for both safety performance (crash-reduction) monitoring as well as functional 

performance (friction, distress, etc.) monitoring. It also provides guidance on end-of-life 

failure, removal, and replacement. 

• Chapter 8 provides information on HFST cost and discussion on methods for funding. 

The cost discussion includes guidance on B/C considerations and estimation for HFST. 

• Appendix A provides some examples of other applications for HFST that are not 

common but have demonstrated the benefits of HFST nonetheless. Appendix B provides 

some examples of systemic deployment of HFST. And Appendix C provides a sample 

inspection checklist for HFST installation. 
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HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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CHAPTER 2—IDENTIFICATION OF HFST CANDIDATE 

LOCATIONS 

There are two primary methods for HFST candidate site identification currently used in the 

United States: 

1. Site-Specific Safety Approach—also known as a hot-spot approach, is a reactive 

approach which uses historic crash data and predictive methodologies such as safety 

performance functions (SPFs) and EB to identify locations where HFST may provide 

benefit. This approach includes identifying sites over-represented with target crashes, in 

this case run-off-road and wet weather crashes, for individual installations. 

2. Systemic Approach—this 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 curves based 

on risk of target crashes where HFST may provide benefit to locations that may not 

have historically observed crashes but are at higher risk for future crashes.

Based on a recent survey of State departments of transportation (DOTs) with HFST 

experience, approximately one quarter of the 26 states responding to the survey indicated that 

they have adopted a systemic approach to installing and managing HFST (Wilson and Saca

2021). 

A third approach, although not discussed in detail in this document, is a policy-based approach 

(also referred to as a systematic approach). With this approach, HFST is effectively specified at 

the design stage of a paving project. HFST is applied at all locations meeting specific criteria 

regardless of crash history at these locations. Typically, the criteria are based on roadway 

characteristics and traffic exposure. This approach is used in the United Kingdom where HFST 

is effectively a standardized pavement surface treatment applied to new and newly-rehabilitated 

pavements. Table 4 shows the locations where HFST (indicated as “HFS” in the table) is 

mandated by design policy using this approach. The table provides the polished stone value 

(PSV) for a given investigatory level (IL).
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Table 4. Modified design policy for use of HFST (“HFS”) in the United Kingdom based on roadway and traffic 

characteristics (Highways England 2020). 

Site 

category

Site description IL

PSV required for given IL. Traffic level and type of site

Traffic (cv/lane/day) at design life

1-

250

251- 

500

501- 

750

75-

1000

1001- 

2000

2001- 

3000

3001- 

4000

4001- 

5000

5001- 

6000

Over 

6000

A Motorway

0.30 50 50 50 50 50 55 55 60 65 65

0.35 50 50 50 50 50 60 60 60 65 65

Q 

Approaches to and across 

minor and major junctions, 

approaches to roundabouts 

and traffic signals

0.45 60 65 65 68+ 68+ 68+ 68+ 68+ 68+ HFS

0.50 65 65 65 68+ 68+ 68+ HFS HFS HFS HFS

0.55 68+ 68+ HFS HFS HFS HFS HFS HFS HFS HFS

K 

Approaches to pedestrian 

crossings and other high risk 

situations

0.50 65 65 65 68+ 68+ 68+ HFS HFS HFS HFS

0.55 68+ 68+ HFS HFS HFS HFS HFS HFS HFS HFS

G1 Gradients 

5-10% longer than 50m

0.45 55 60 60 65 65 68+ 68+ 68+ 68+ 68+

0.50 60 68+ 68+ HFS HFS HFS HFS HFS HFS HFS

S2

Bends radius <500m – 

carriageway with two-way 

traffic

0.45 50 55 60 60 65 65 68+ 68+ HFS HFS

0.50 68+ 68+ 68+ HFS HFS HFS HFS HFS HFS HFS

0.55 HFS HFS HFS HFS HFS HFS HFS HFS HFS HFS
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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Deployment of HFST typically begins with installation of HFST at a few experimental locations, 

or spot treatments, to allow agencies to test the usefulness and application of the treatment. 

These spot locations are typically high-crash locations where inadequate pavement friction is 

believed to be a contributing factor in a significant number of the reported crashes. After initial 

experimental installations, agencies may expand the spot treatment approach on a large scale, 

consolidating multiple application locations under one contract. This treatment approach can 

quickly reveal the effectiveness of HFST such that it gains agency-wide acceptance, helping to 

convince policymakers of the benefits of this life-saving treatment. 

Agencies comfortable with a systemic safety approach for other countermeasures may choose 

to add HFST as an option, resulting in a larger-scale systemic deployment. Other agencies may 

promote HFST deployment through Road Safety Audits (RSAs), Roadway Departure Safety 

Implementation Plans (RwDSIP), or in Highway Safety Improvement Program (HSIP) guidelines. 

Regardless of the method for implementation, agencies will benefit from documenting locations 

to track the safety performance of HFST installations for further fine-tuning of the site selection 

process and widespread deployment.

Agencies typically evaluate crash data through a network screening process to identify HFST 

candidate locations. Whether this is spot location crash data or crash data analyzed as part of a 

systemic approach, safety performance is the key justification for HFST implementation as it 

does not provide any benefits relative to pavement preservation. 

The following sections discuss the more common methods for HFST candidate site

identification currently used by agencies throughout the United States as well as new methods, 

such as pavement friction management programs (PFMPs), also being implemented for the 

purpose of site selection. While the focus of this Guide is on HFSTs on horizontal curves and 

ramps, it also discusses using HFST to reduce crashes at intersections. Appendix A highlights 

additional applications that have not seen widespread use but have shown great potential. 

Regardless of the method used for initial identification, field verification of candidate locations is 

an essential component of HFST implementation and will be discussed further in chapter 3. 

2.1 SITE-SPECIFIC SAFETY APPROACH 

A site-specific safety approach focuses on reducing crashes at locations with high crash 

frequency. Agencies using this approach for HFST typically use a roadway network screening 

process to identify locations with a disproportionate number of crashes. Some agencies set a 

specific threshold crash frequency, above which the location is automatically recommended for 

potential countermeasure development. Other agencies use a ranking system by developing a 

list of locations that exhibit a significantly high concentration of collisions. They investigate the 

highest ranked locations on the lists, develop a list of potential countermeasures for each 

location, and select as many locations as possible for treatment based on funding availability and 

expected return on investment. Much of the following discussion is focused on HFST for 

horizontal curve applications, but the same principles apply to other locations such as ramps 

and intersections. 
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When selecting locations for HFST, some agencies look at the total crash frequency, wet-crash 

frequency, RwD crash frequency, and crash severity (i.e., focusing on fatal or serious injury 

crashes). For each crash, they may examine the crash report narrative to determine the factors 

contributing to the crash and to pinpoint the exact location within the curve. As crashes may 

occur or be recorded as happening before or after the horizontal curve, it is important to verify 

the location of the crashes in order to determine whether each crash belongs in the data set.

2.1.1 SPFS AND EB PROCESSES 

The primary reason for implementing HFST is to prevent or mitigate future crashes. To 

maximize the actual return on investment, HFST should be applied at locations with the 

greatest potential to reduce number and severity of friction-related future crashes. Historically, 

observed crash frequency is one means of estimating the potential for future crashes at a given 

location. The Highway Safety Manual (HSM), published in 2010 by the American Association of 

State Highway and Transportation Officials (AASHTO), describes limitations of relying solely on 

recent crash history to identify locations with the greatest potential for improvement. These 

limitations include the natural variability in crash frequency, regression-to-the mean bias, and 

changes in roadway characteristics over time. The HSM provides predictive methods that 

address these limitations through SPFs and EB weighting of observed crash frequencies and SPF 

estimates.

SPFs are equations used to predict the average number of crashes per year at a location as a 

function of site characteristics. Site characteristics always include exposure (typically average 

annual daily traffic, AADT), but may also include roadway characteristics such as number of 

lanes, lane width, median and shoulder features, radius, or degree of curvature (Srinivasan et al. 

2013; Donnell et al. 2019). Recent efforts have led to the development of SPFs which consider 

pavement friction (de León Izeppi et al. 2016a, de León Izeppi et al. 2016b, Pratt et al. 2018b). 

However, the regression coefficients for these SPFs are specific to the jurisdiction where

friction data were collected and are specific to the device used to measure friction. While these 

SPFs may not be transferable across jurisdictions, agencies can use the documented process to 

develop their own friction-based SPFs (de León Izeppi et al. 2016a, de León Izeppi et al. 2016b). 

Agencies can use SPFs in the network screening process for identifying HFST candidate 

locations. Specifically, agencies can use SPFs to predict crashes for a particular location and then 

compare the estimate to the observed number of crashes at the location, ranking candidates 

based on the difference (i.e., the greater the difference between observed and predicted, the 

higher the priority for treatment). This network screening process can further be improved by 

computing the expected number of crashes through EB weighting of predicted and observed 

crashes. The excess expected crashes (EEC) measure is the difference between expected crash 

frequency and SPF-predicted crash frequency at the location. 

The EB expected crash frequency can provide a more reliable estimate of the site’s long-term 

average crash frequency than the observed crash history. However, the reliability of the EB 

approach is dependent upon the SPF used for predicting average crash frequency. Agencies may 
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choose to develop their own SPF or to calibrate existing SPFs to the local data. It is important 

for agencies to consider the cost of SPF development versus calibration, the amount of data 

required, and general availability and quality of data. One option is to first calibrate an existing 

SPF to local data and determine how well the calibrated SPF performs based on goodness-of-fit 

measures and a cumulative residual plot. The cumulative residual plot provides an indication of 

how well the calibrated SPF performs for a breadth of sites stratified by exposure (AADT) and 

other continuous variables such as calibrated predictions. This stratification is important to 

determine if the SPF shape is appropriate (a calibrated model cannot change the shape of the 

SPF). If the calibrated model does not provide good fit to the overall data, then SPF 

development may be necessary. FHWA’s Safety Performance Function Decision Guide: SPF 

Calibration vs SPF Development provides further details (Srinivasan et al. 2013). 

2.1.2 WET PAVEMENT CRASHES 

Wet pavement conditions can lower the available pavement friction drastically, particularly if 

the pavement has been polished by traffic wear and lacks adequate macrotexture to allow 

water to evacuate between the tire and pavement surface. HFST is an ideal countermeasure for 

these conditions because it can increase pavement friction values up to 300 percent. (Note that 

friction measurements are typically performed on a wetted pavement surface.) As 

demonstrated by the CMFs presented in table 2 and table 3, the greatest crash reduction 

benefit (i.e., lowest CMF) is for wet-pavement crashes (Merritt et al. 2020b). 

Most agencies focus heavily on wet crashes as a screening criterion for identifying HFST 

candidates. These locations are typically identified as either having a high frequency of wet 

crashes year after year or as having a high ratio of wet-to-dry or wet-to-total crashes. The 

process by which agencies select wet crash curve locations for potential HFST implementation 

varies. For example, agencies may develop a list of locations that have experienced a specific 

number of wet crashes within a single time period (e.g., 20 or more wet crashes in 5 years) or 

incremental time periods (e.g., 3, 6, or 9 wet crashes in 1, 2, or 3 years, respectively). Although 

not common practice, agencies may even normalize the yearly wet crash frequency by historical 

percent wet-time values obtained per location, to understand the overrepresentation of wet 

crashes for locations that are either particularly wet or dry. Wet crash ratios of 0.35 wet/total 

crashes (Von Quintus and Mergenmeier 2015) or 50-percent wet/dry crashes (PennDOT 2012) 

are two examples of these criteria. 

In addition to wet pavement crashes, States that experience snow and ice conditions in the 

winter months have also reported a reduction in snow and ice crashes from HFST. The South 

Dakota DOT, for example, has 5 times more RwD crashes involving winter road conditions 

than wet road conditions. While there were not enough data to perform an advanced statistical 

analysis of crash reductions, a naïve before-after analysis showed an 80-percent crash reduction 

(77 percent with the Winter Severity Index applied) in 3 years at 4 initial HFST demonstration 

projects, and a 78-percent crash reduction in 2 years after HFST was installed at 15 additional 

locations (FHWA 2019). While HFST has shown potential to reduce snow and ice crashes, 
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winter road conditions can be highly variable (e.g., icy, snow-packed, slushy, etc.), and therefore 

crash reduction benefits will also likely be highly variable. 

2.1.3 ROADWAY DEPARTURE CRASHES 

From 2016-2018 RwD crashes accounted for 51 percent of all traffic fatalities in the United 

States (FHWA 2020b). HFST is recognized as a proven countermeasure for reducing RwD 

crashes by helping to keep vehicles in their lane (FHWA 2021a). A 2018 NCHRP synthesis 

revealed that 90 percent of the States that responded to a survey on RwD countermeasure 

usage have deployed HFST for reducing RwD crashes, with 20 States indicating they use it often 

or at least sometimes. The survey also revealed HFST as one of four RwD countermeasures 

responding States deemed to be especially effective in reducing the frequency or severity of 

RwD crashes (McGee 2018). States are including HFST in their Roadway Departure Safety 

Implementation Plan. 

A benefit of HFST compared to other curve-related RwD countermeasures (e.g., edge line or 

shoulder rumble strips, edge line pavement markings, horizontal curve delineation, etc.) is that 

HFST does not depend on the driver to recognize the information associated with delineation 

or noise/vibration and make corrections. Rather, HFST interacts directly with the vehicle, 

independent of the driver’s awareness, by providing the necessary friction needed to help keep 

the vehicle on the roadway.

While rural RwD crashes account for a significant percentage of RwD crashes (approximately 

34 percent of all fatalities), these crashes tend to be spread out across long sections of roadway

(FHWA n.d.). As such it is not often feasible to address rural RwD crashes through traditional 

site-specific (“hot spot”) methodologies, and systemic approaches are necessary (Torbic et al. 

2020). While formal results are not yet published, Louisiana and Georgia are two States which 

have deployed HFST for reducing rural RwD crashes using a systemic approach (McRae 2020, 

Tsai et al. 2018). 

2.1.4 INTERSECTION CRASHES 

Intersections are another key application for HFST. Pavement friction is necessary at 

intersections to help vehicles stop and start, which can also cause pavements to polish or wear 

more quickly than other sections of pavement. Higher friction at the approach to an 

intersection shortens stopping distance to reduce rear-end crashes and reduce crosswalk 

incursions for pedestrian safety. Higher friction within an intersection potentially reduces the 

occurrence or at least the severity of right-angle crashes. Because the number of intersection 

applications of HFST in the United States to date has been limited, there is little published 

information on the effectiveness of HFST for intersections. 

The Ministry of Transportation and Infrastructure, British Columbia applied HFST at 10 

signalized intersection approaches in 2019. Intersection locations were identified and ranked 

using an “excess proportion of specific crash types” method (HSM countermeasure-based 

approach), with rear-end crashes as the target crash type. Although initial anecdotal evidence 
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19 

suggests a significant reduction in rear-end crashes at these locations, a formal before-after 

analysis has not been completed and published. 

Other studies have demonstrated the impact of friction enhancement (through traditional 

resurfacing or microsurfacing) in reducing rear-end crashes at intersection approaches. One 

such study from New York State DOT’s Skid Accident Reduction Program revealed significant 

reduction in total, wet-road, rear-end, and rear-end wet-road crashes, with less significant 

benefit for right-angle crashes. For this study, crashes within 33 ft of the intersection were 

considered intersection-related crashes (Harkey et al. 2008). 

2.1.5 CRASH SEVERITY

While some agencies prioritize improvement locations by the frequency and severity of crashes, 

it is also important to capture where frequent non-severe or property-damage-only (PDO) 

crashes occur. These less severe crashes may be predictors of future serious injury or fatal 

crashes, if left untreated. Additionally, the cost of non-severe crashes can become substantial if

they are happening frequently. Many agencies use a weighted scale to assign either numeric or 

monetary values to each crash severity level, in order to capture instances where frequent, less 

severe crashes may accumulate to a situation that requires addressing. FHWA’s Crash Costs for 

Highway Safety Analysis provides a method to assign monetary values to an injury level scale (the 

KABCO scale) (Harmon et al. 2018). 

By using the KABCO scale, or similar, agencies may be able to identify a threshold at which 

horizontal curves, ramps, or intersections with few fatalities or serious injuries, but frequent, 

less severe crashes can be identified and treated.
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Evolution of KYTC’s HFST Site Selection Process

Initial Demonstration 

Project

KYTC’s initial experience with HFST was a smallerscale demonstration installation at two locations with a 

high number of wet pavement crashes. Based on the 

dramatic decrease in crashes in the 4 years following 

installation, KYTC looked for more opportunities for 

HFST.

First Iteration

KYTC identified 30 locations with high RwD crashes

that could potentially benefit from HFST using a 

wet/dry crash ratio greater than 50 percent as 

screening criteria.

Second Iteration

As part of their RwDSIP, KYTC analyzed 4 years of 

crash data on rural roadway segments (3,000 ft in 

length) and identified HFST candidates based on a 

screening criterion of 8 wet crashes and a wet/total 

crash ratio of 0.35. This resulted in 227 candidate sites 

of which 160 were selected for installation after field 

assessment. 

Third Iteration

KYTC has adopted an EB methodology for network 

screening of potential HFST candidate locations. This 

methodology uses wet-weather RwD SPFs with EB 

adjustment to determine EEC values for different 

facility types (curves and ramps) and for the different 

crash severities (i.e., K, A, B, C, O). The EEC values are 

then used with crash severity to prioritize locations for 

treatment.

Potential Future 

Enhancements

KYTC is currently collecting 15,000 miles annually of 

network-wide data using continuous friction 

measurement for the purpose of a preventative 

systemic approach. It is expected that incorporating 

continuous friction measurement data into SPF models 

will be a more effective and efficient systemic approach 

than one without friction data 

2.2 SYSTEMIC APPROACH 

A systemic approach to HFST site selection is a proactive approach that allows an agency to 

identify candidate locations based on high-risk roadway features that are correlated with 

particular crash types, rather than crash frequency (23 USC 148(a)(12)). In other words, 
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systemic site selection is not based on crash history at a particular location but is based on a 

high probability of future crashes at that location. 

The systemic approach does not replace the need to focus on individual locations with high 

numbers of severe crashes, but simply expands site selection to a more comprehensive and 

proactive approach to roadway safety efforts. Agencies can use the systemic approach to 

address the requirements for the HSIP, which focuses on fatal and serious injury crashes on all

public roads. Additional information on balancing site-specific and systemic approaches to safety 

countermeasures is provided in the Reliability of Safety Management Methods: Systemic Safety 

Programs (Gross et al. 2016). 

2.2.1 THE PROCESS

The systemic approach to safety involves widely implementing low-cost safety improvements, 

such as HFST, based on high-risk roadway features correlated with specific severe crash types. 

The approach provides a more comprehensive method for safety planning and implementation 

that supplements and complements traditional site-specific analysis. The approach helps 

agencies broaden their traffic safety efforts and consider risk as well as crash history when 

identifying where to make low-cost safety improvements. Note that the systemic process 

typically considers many different countermeasures, and it may or may not lead to selecting 

HFST as the recommended safety countermeasure. HFST has been identified as a 

countermeasure for roadway segments (i.e., curve treatments) and is currently being evaluated 

as a systemic countermeasure for intersections. 

The key to the systemic approach is evaluating an entire system using a defined set of criteria, 

which results in an inferred prioritization that indicates some elements of the system are better 

candidates for safety investment than others. Section 2.2.4 provides risk factors used by 

agencies that have included HFST as a countermeasure in the systemic approach. 

The following are three common approaches or tools used for a systemic evaluation. For each, 

there is an indication of the basic data needs. Which tool an agency chooses to use will depend 

largely on the availability of crash and roadway data (Torbic et al. 2020).

• FHWA Systemic Safety Project Selection Tool Methodology—this is the least 

complex and most adaptable tool for agencies with incomplete or lower quality roadway 

inventory, traffic volume, and/or crash data. This tool allows for prioritization of sites 

with potential for safety improvement and related projects without the need for highquality crash data (Preston et al. 2013). If quality crash data are available, there is an 

opportunity to include observed, predicted, or expected crash frequency as a risk factor 

in systemic site selection.

• Application of SPFs Using State-Specific In-House Tools—this methodology 

requires a special skill set (i.e., ability to develop and calibrate SPFs), and relies on highquality robust roadway inventory, traffic volume, and crash datasets. Further, there is an 

opportunity to use the results from an EB-based network screening as a starting point 

for systemic safety analysis. 
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• Application of U.S. Road Assessment Program (usRAP) Methodology and 

Vehicle Information and Diagnostics for Aftersales (ViDA) Software—this is a 

more defined and methodological approach but requires robust roadway datasets

(usRAP n.d.). 

2.2.2 BENEFITS OF THE SYSTEMIC APPROACH

Agencies may see several benefits when using the systemic approach for HFST. The systemic 

approach: 

• Identifies “issues” based on a system-wide analysis of the data. A significant number of 

severe crashes are spread over a wide area and relate to specific crash types. Some of 

these crashes are rarely identified through the traditional site analysis approach because 

it is difficult to isolate severe crash locations. The systemic approach provides State, 

regional, and local transportation agencies an alternative method to address severe, 

targeted crash types and fulfill a previously unmet need (Atkinson et al. 2016). 

• Looks for roadway characteristics that are frequently present in severe crashes (i.e., risk 

factors). The systemic approach starts with a different premise for identifying safety 

concerns. While the site-specific approach is based on crash history at individual 

locations, the systemic approach looks at crash history on an aggregated basis to identify 

high-risk roadway characteristics that may contribute to future severe crashes. The sitespecific approach results in safety investments at high-crash locations while the systemic

approach leads to widespread implementation of low-cost improvements to reduce the 

potential for severe crashes (Atkinson et al. 2016). 

• Focuses on one or more low-cost countermeasures that can be deployed widely across 

the system while identifying and prioritizing implementation locations. The systemic 

approach considers multiple locations with similar risk characteristics. When examining 

the system as a whole, a particular roadway characteristic may contribute to frequent or 

severe crash experiences. It can be more cost-effective to address some issues on a 

system-wide basis (or at least a wider deployment of countermeasures) rather than by 

individual crash location (Atkinson et al. 2016). 

• Is a data-driven approach that is adaptable based on available data. Various options are 

available depending on the quality of the crash data available. This is beneficial for local 

agencies that may have very limited roadway inventory and traffic data, as well as 

incomplete or poor-quality crash data (Torbic et al. 2020).

2.2.3 CHALLENGES 

One of the biggest challenges of implementing a systemic site selection process is related to the 

evaluation and justification of prior systemic strategies or programs. This stems from the fact 

that evaluations use several years of crash data after implementation. Therefore, results lag 

behind initial deployment for several years (Torbic et al. 2020). This can make assessments of 

the effectiveness (and justification to decision-makers for further funding) difficult. It can also 
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23 

make identification of necessary adjustments to the process for future deployments difficult to 

determine. Other challenges associated with implementing a systemic site selection process 

include: 

• Data availability dictates the level of detail in the analysis. While a systemic analysis can 

be completed with nearly any amount of data, using more data will allow for refinement 

of potential risk factors.

• The availability of resources determines the extent of improvements that can be made. 

Resources may also impact the level of analysis that can be completed.

• The established priorities of an agency may define the direction of the analysis.

• The relationship between State and local transportation agencies may impact the funding 

available for systemic analysis on non-State routes as well as the extent to which 

systemic improvements are applied to non-State routes.

2.2.4 EXAMPLES OF SYSTEMIC APPROACHES FOR HFST

Agencies utilizing a systemic approach for HFST site selection have typically focused on rural 

RwD curve crashes. Two agencies, Louisiana Department of Transportation and Development 

(DOTD) and Georgia DOT, implemented systemic deployments that did not consider crash 

history at the specific locations selected for treatment, but rather treated curves based on risk 

criteria (Tsai et al. 2018, McRae 2020). Two other agencies, Thurston County, Washington, and 

Delaware DOT used systemic processes for identification of candidate locations based on risk 

factors, and focused treatment on specific locations with high potential for safety improvement

(Davis 2014, Weiser 2016). Appendix B includes additional detail on these agencies’ systemic 

processes. 

The general risk factors used by these agencies for systemic deployment of HFST for RwD 

crashes at curves includes:

• Facility type: rural/local roads, arterials and collectors (typically two-lane). 

• Traffic Volume: low to medium traffic volume with AADT ranging from 2,500-8,000 

vehicles/day. 

• Geometrics: sharp horizontal curves (degree of curvature > 3.5, radius < 1,640 ft) with 

and without grade. 

• Grade: greater than 4 percent. 

• Shoulders: narrow paved or unpaved/native shoulders (less than 6 ft). 

• Speed: typically, higher speed such as 50 miles per hour (mph) speed limit. 

• Ball-bank indicator readings: 12 or higher. 

As agencies develop PFMPs and identify appropriate investigatory levels based on site 

conditions, pavement friction will likely become another risk factor for inclusion in systemic 

programs. 
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2.3 PAVEMENT FRICTION 

As a countermeasure specifically used to enhance pavement friction, HFST deployment usually 

focuses on locations with a “friction issue” that may be contributing to observed crashes or 

may lead to crashes in the future. A high percentage of lane departure crashes and wet 

pavement crashes are key indicators that a friction issue may already exist. Systemic site 

selection processes may further be able to identify locations with the potential for friction 

issues through an evaluation of risk factors. As discussed in chapter 3, friction testing as part of 

HFST candidate site verification confirms that a friction issue exists or if there may be other 

contributing factors. 

While pavement friction can be measured directly, there is no universally accepted friction 

value that indicates adequate friction for all locations (AASHTO 2008). Rather, adequacy of 

pavement friction is evaluated based on the concepts of friction demand and margin of safety, 

discussed in section 2.3.1. Furthermore, proactive approaches such as PFMPs using appropriate 

testing methodologies and devices can help to identify potential friction issues before they 

manifest in the form of increased crash rates, and help agencies establish appropriate levels of 

friction based on site characteristics. 

2.3.1 FRICTION DEMAND AND MARGIN OF SAFETY

Friction demand is the level of friction needed to safely perform braking, steering, and 

acceleration maneuvers (AASHTO 2008). Friction demand is a function of vehicle speed and 

roadway geometry (curve radius, superelevation rate, grade) as well as driver behavior (e.g., 

how a driver navigates a curve with respect to travel path braking and acceleration). 

Furthermore, for curve locations in particular, driver behavior may be influenced by roadway 

geometry as it affects driver comfort, which in turn may influence the speed at which they 

approach and navigate a curve. Friction demand increases as speed increases and curve radius 

or superelevation rate decrease. For non-curve and other high-risk locations such as steep 

grades, intersection approaches, pedestrian crossings, and roundabouts, friction demand is 

driven by the ability to perform short-term maneuvers such as sudden braking, lane changes, 

and minor changes in direction within a lane (AASHTO 2008). 

Friction supply is the available pavement-tire friction capability. It is affected by tire-pavement 

interface properties (e.g., tire tread condition), pavement texture, and the presence of water or 

solid contaminants on the pavement surface (Pratt et al. 2014). 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, is necessary for 

good pavement friction. 

Figure 3 illustrates conceptually the relationship between friction demand, friction supply, and 

vehicle speed. Note that the greater the friction supply, the greater the capability of handling 

friction demand as speed increases (i.e., the higher the speed of impending skid). 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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© AASHTO

Figure 3. Graphic. Relationship between speed, friction demand, and friction supply

(AASHTO 2008). 

Locations with high friction demand are prone to losing friction over time as the surface wears 

or polishes faster than pavement with low friction demand, all else being equal. This 

necessitates a pavement surface that not only provides the necessary levels of friction to meet 

friction demand, but also one that can sustain those friction levels over time. HFST provides 

exceptional levels of friction and sustains high levels of friction over time under traffic wear. 

Margin of safety is the difference between friction supply from the pavement surface and friction 

demand from vehicles traversing the surface (Pratt et al. 2014). If friction demand exceeds 

friction supply, vehicle skidding is likely to occur. 

A larger margin of safety allows for drivers to compensate for mistakes such as driving too fast 

for conditions. Margin of safety can be increased by increasing friction supply or by decreasing 

friction demand. Decreasing friction demand can be much more challenging as it may require 

altering the geometry of the roadway (e.g., increasing curve radius or superelevation rate) or 

reducing vehicle speed, which is dependent upon driver behavior (Pratt et al. 2014). Increasing 

friction supply, however, can be accomplished fairly simply through the application of HFST 

which provides substantially higher friction values than conventional pavement surfaces and 

other surface treatments. 

The Texas Transportation Institute (TTI) developed the Texas Curve Margin of Safety (TCMS) 

tool (Pratt et al. 2018a, Pratt et al. 2018b) to evaluate the margin of safety for curves. This tool 

considers the influence of driver behavior in navigating curves in order to provide a better 

estimate of the margin of safety. The procedure uses roadway geometry (curve radius, 

deflection angle, superelevation rate, and grade) and vehicle speed (85th percentile on the 

approach and curve midpoint) to estimate friction demand at the beginning point of curvature 

(PC), midpoint, and end point of tangency (PT) of a curve. For friction supply, the tool 

considers the maximum available side friction supply as a function of friction measured through 

standard locked-wheel skid testing procedures along with consideration of a reduction in side 

friction supply due to acceleration and/or braking tractive friction. Friction demand is compared 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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to friction supply to determine the margin of safety at three points (PC, midpoint, and PT) 

along the curve. A margin of safety of at least 0.08 to 0.12 is suggested along the entire length 

of the curve (Pratt et al. 2014, Glennon and Weaver 1971). 

Agencies input friction supply either directly from friction measurements or from default values 

for common pavement surfaces and treatments, including HFST. Friction change over the life of 

the treatment is modeled for the purpose of evaluating changes in the margin of safety over 

time. Safety prediction models for curves on two-lane, four-lane undivided, and four-lane 

divided roadways are also included in the tool and use CMFs for total crashes, run-off-road 

(ROR) crashes, and wet weather ROR crashes based on curve radius, skid number, lane width, 

shoulder width, and annual precipitation. The safety prediction analysis is further used to 

perform a B/C analysis for assessing the long-term benefits of different pavement 

surfaces/treatments (Pratt et al. 2018b). While there are currently no known similar tools for 

assessing margin of safety for intersections, the basic principles still apply. 

2.3.2 PAVEMENT FRICTION MANAGEMENT PROGRAMS 

PFMPs are a proactive and systematic approach to measuring and monitoring pavement friction 

and crash risks (wet and dry) of roadways, such that pavement surfaces in need of remedial 

action (e.g., friction improvement with HFST) can be readily identified and treated (AASHTO 

2008, de León Izeppi et al. 2019). 

FHWA Technical Advisory R 5040.38 provides general guidance on what should be considered 

in a PFMP, and the AASHTO Guide for Pavement Friction provides additional detail on the 

various aspects of a PFMP. However, it should be noted that while the FHWA Technical 

Advisory generally focuses on wet-weather crash locations, numerous studies have found that 

HFST also helps reduce dry pavement crashes. Current efforts to develop PFMPs recommend 

the following steps for implementation (de León Izeppi 2019):

1) Pavement Network Definition—The roadway network is divided into distinct 

pavement sections based on friction demand categories. Factors affecting friction 

demand categories include: roadway alignment (horizontal and vertical), roadway 

features/environment or “events” (ramps, driveways, intersections, median type, urban 

vs. rural setting, etc.), traffic characteristics (traffic volume, composition, and speed), and 

driver/vehicle characteristics. 

2) Network-Level Data Collection and Processing—Agencies establish field testing 

procedures for collecting friction, texture, and geometric data. Friction testing 

parameters agencies need to define include: season for testing, test speed, test lane and 

wheelpath, and ambient conditions. Agencies also collect and use crash data, traffic data, 

and pavement condition data (e.g., distress, smoothness, etc.) in the safety analysis. 

For friction measurement, continuous pavement friction measurement (CPFM) methods

provide a more comprehensive “map” of pavement friction, as opposed to spot 

measurements representing only a short section of pavement from a locked-wheel skid 
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trailer test which will only measure 1-2 percent of the pavement surface (de León Izeppi 

et al. 2019). This allows agencies to identify variations in friction, which may occur 

within a given pavement section. This is particularly common for sections with high 

friction demand due to accelerated wear of the surface (e.g., horizontal curves, 

intersection approaches, steep grades, etc.). These sections commonly have the worstcase friction condition and may not traditionally be measured due to safety concerns for 

data collectors. Recent evaluations have demonstrated the benefits of CPFM for PFMPs, 

and there are several CPFM devices currently available for collecting continuous friction 

data (de León Izeppi et al. 2016a). Most modern friction measurement devices also 

collect texture and roadway data simultaneously (FHWA 2021b). 

3) Threshold Analysis—Friction, roadway characteristics, and crash data are analyzed to 

help define friction demand categories and to determine appropriate ILs for friction. The 

IL is considered a desirable level of friction (based on site characteristics/friction 

demand) and if friction falls below this value, further investigation of a location should be 

performed. These thresholds can be determined from an evaluation of crash rates and 

historical pavement friction measurements for each friction demand category (AASHTO 

2008). These friction thresholds will be specific to the device used to measure friction 

unless measurements from different devices have been harmonized. 

4) Safety Analysis—Agencies use SPFs and the EB methodology to analyze crash data 

and determine the expected crash counts based on friction demand categories. As an 

agency’s PFMP evolves, they can develop SPFs that consider friction or CMFs that 

consider friction change from various treatment types for better estimation of the 

impact of pavement friction on crashes. 

5) Network Screening—Agencies screen network-level friction data to identify 

pavement sections that fall below the ILs for potential friction treatments. 

6) Benefit-Cost Analysis for Selection of Friction Treatments—In this step, 

agencies use the EB approach to predict the potential crash reduction and compute the 

crash reduction savings. Agencies then use the cost of various treatments and 

anticipated life to compute a B/C for each treatment to facilitate treatment selection 

and prioritize treatment locations. 

This process is then repeated annually to help further refine friction demand categories, friction 

ILs, SPFs, and B/C ratios for different treatments. 

A significant benefit of a comprehensive PFMP is that friction data can be used to potentially 

identify all friction-related crashes in a network, rather than just wet pavement crashes (de 

León Izeppi et al. 2016a). While wet pavement crashes are typically used as a network 

screening criterion to identify HFST candidate sites, HFST is also effective at reducing dry 

pavement crashes. Further, the benefits of a PFMP can far outweigh the costs and effort to 

develop and deploy such a program. A pilot PFMP study from Virginia found that the potential 

economic savings from crash reduction realized through the deployment of a comprehensive 
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PFMP would offset the costs, including the equipment necessary for data collection using CPFM

and the cost of friction treatments (de León Izeppi et al. 2016a). 

2.4 SPEED DIFFERENTIALS FOR CURVES 

For horizontal curves, speed differential is defined as the difference between the tangential 

posted regulatory speed limit (e.g., at the approach to a curve) and the curve advisory speed, or 

more importantly, the speed at which drivers navigate a curve (i.e., 85th percentile curve speed). 

Speed differential can be a good indicator of the usefulness of an HFST treatment as side 

friction demand increases with increasing speed reduction due to deceleration as vehicles enter 

a curve (Bonneson 2007). As figure 4 illustrates, for a given curve radius and curve speed (85th

percentile speed), speed differential increases with the 85th percentile tangent speed (Pratt et al.

2014). Under wet weather or low pavement friction conditions, friction supply may be 

inadequate for this increased side friction demand, and skidding or a RwD crash may result. 

HFST provides additional friction to allow motorists to break and navigate successfully without 

losing control.

Figure 4. Graphic. Increase in speed differential (Pratt et al. 2014).

 

Studies have linked curve radii to crash likelihood, with crash rate increasing with a decrease in 

curve radius, particularly below 1,000 ft. Since a smaller curve radius corresponds to a lower 

advisory speed and a greater speed differential, radius and speed differential can be deductively 

linked in many cases. In addition to curve radius, other studies have examined the relationship 

between the length of tangent upstream and downstream from a curve. Although not defined 

explicitly in terms of tangent length, longer upstream and downstream tangents result in a 

higher number of RwD crashes, while shorter upstream and downstream tangents result in 

lower RwD crashes (Donnell et al. 2019).
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2.5 ROADWAY GEOMETRY 

Superelevation and roadway grade are other geometric factors that affect friction demand and 

the potential need for HFST. Superelevation is accounted for in the AASHTO Green Book 

equation for friction demand (AASHTO 2018a). A lack of superelevation increases friction 

demand and is commonly found in the first and last portions of most curves where 

superelevation is not fully developed. Increasing friction using HFST can help counteract a lack 

of superelevation. Roadway downhill grade greater than four percent has been reported to 

have an impact on ROR crashes on sharp curves (Tsai et al. 2018). To account for roadway 

grade, a modified version of the AASHTO Green Book friction demand equation which 

accounts for grade is proposed by Pratt et al. and incorporated into the margin of safety tool 

discussed previously (Pratt et al. 2014). 

Roadway geometry can also impact friction demand at intersection approaches. Intersections at 

the bottom of a downward grade, for example, require additional braking distance. Limited 

sight distance at an intersection approach, likewise, can increase friction demand as drivers 

react suddenly to a stoplight or stop sign. Increasing friction supply through the use of HFST 

can counteract increased friction demand at these critical locations (FHWA 2020a). 
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Roadway Characteristics Site Selection Processes

Recognizing the importance of roadway 

geometry and the interaction of 

friction, superelevation, curve radius, 

and speed, Georgia DOT used a 

ballbank indicator (BBI) to help identify 

curves with potential high friction 

demand as part of their systemic 

deployment of HFST, regardless of 

crash history. Current efforts are 

underway to use curve characteristics 

data measured using automated data 

collection methods to identify high-risk 

locations based on these characteristics 

(Tsai et al. 2018).

TTI’s TCMS tool also accounts for 

speed differentials and roadway 

characteristics in computing margin of 

safety for HFST curve candidate 

locations (Pratt et al. 2014, Pratt et al.

2018a, Pratt et al. 2018b, Pratt et al.

2020).
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CHAPTER 3—FIELD VERIFICATION AND DESIGN 

Once an agency identifies, either through crash history or systemic site selection processes, 

HFST candidate locations the next step is field verification and determining whether HFST 

should be implemented at a given location. Field verification helps to identify site factors that 

are not readily apparent from the crash data analysis or roadway characteristics information 

used for site selection. Field verification may even help identify the need for safety 

countermeasures other than or in addition to HFST. In addition to helping assess the suitability 

of a candidate location, field verification also helps to identify design factors that can impact the 

cost of the HFST installation. 

3.1 FIELD VERIFICATION 

Key factors which should be included and addressed as part of the field verification process are 

discussed below. Consideration should be given to conducting the field review during the 

timeframe or conditions of collision patterns (e.g., time of day, season, light conditions, 

pavement condition). Agencies should collect copious notes, accompanied by photos and 

videos, during the field visit, particularly if they are reviewing numerous sites. 

1) Pavement Friction—Because HFST is specifically used to enhance pavement friction, 

verification of a “friction issue” at an HFST candidate location is one of the most critical 

aspects of field verification. If an agency uses data from a PFMP to screen and identify

HFST candidates, confirmation testing may not be necessary. Agencies can perform 

additional testing for locations where PFMP or routine network-level friction data are 

unavailable. Verification testing should include the limits of the treatment area as well as 

surrounding (upstream and downstream) pavement to identify variations in friction at 

the candidate location. 

As discussed in chapter 2, CPFM provides a better indication of friction variation 

through a curve or at an intersection approach than spot friction. Spot friction tests may 

not adequately capture differences in friction through the treatment area. 

Assessment of whether there is a friction issue will depend on the friction demand for 

the location. Chapter 2 describes methods for assessing friction demand in more detail. 

If an agency determines that the pavement friction is adequate, they may investigate 

other potential causes of the crashes. 

2) Pavement Condition—The condition of the pavement surface where the HFST is to 

be installed has a major impact on the longevity of the treatment. Highly distressed 

pavements will diminish the lifespan of HFST, regardless of the integrity of the HFST 

itself as HFST does not provide any pavement preservation benefit. 

With experience, agencies should establish pavement distress criteria for which HFST 

will not be permitted until the structural integrity of the existing pavement has been 

restored. Pennsylvania DOT (PennDOT) does not allow placement of HFST over 
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structurally inadequate pavement, and has guidelines on whether HFST should be 

installed based on pavement condition, as shown in table 5 and table 6 (PennDOT 

2019). 

Table 5. PennDOT guidelines for HFST usage on asphalt pavements.

Existing Asphalt Pavement Condition HFST Allowable 

Usage

Project Length ≤ 1,500 feet YES

Project Length > 1,500 feet MAYBE

Low Severity Rutting (1/8 inch or less) YES

Medium Severity Rutting NO

High Severity Rutting NO

Low Severity Fatigue Cracking (hairline or smaller) YES

Fatigue Cracking NO

Low Severity Edge Deterioration YES

Permanent Asphalt Patching (Less than 1%) YES

Non-Permanent Asphalt Patching NO

Bleeding NO

Raveling NO

Raveling or Weathering NO

Table 6. PennDOT guidelines for HFST usage on concrete pavements.

Existing Concrete Pavement Condition HFST Allowable 

Usage

Project Length ≤ 1,500 feet YES

Project Length > 1,500 feet MAYBE

Permanent Concrete Patching YES

Non-permanent Concrete Patching NO

Low Severity Cracking (hairline or smaller) YES

Low Severity Joint Spalling (1 inch or less) YES

Joint Spalling NO

Broken Slabs NO

Faulted Joints NO

While many agencies maintain annual pavement condition surveys on primary roadways 

which could be used for an initial screening of pavement condition, current condition 

information is likely not available for secondary and local roadways. Regardless of the

availability of pavement condition data, field verification is always a recommended 

practice. 
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In addition to pavement distress, an additional pavement condition issue is subsurface 

moisture migration. Poor subsurface drainage can result in moisture migrating upward 

from beneath the pavement. This condition could impact installation of HFST as resin 

binders do not bond well to saturated pavement surfaces and could also lead to a 

shortened pavement life as the HFST may serve to trap moisture in the underlying 

pavement surface layer. This issue (if suspected to be present) will need to be verified 

through a field visit and possibly also through discussions with local maintenance 

personnel. 

3) Physically Locating Crashes—Physically locating crashes within a given curve, ramp, 

or intersection candidate location will help provide a better understanding of potential 

contributing factors to observed crashes and will also help establish the necessary HFST 

treatment limits. Bringing a populated crash report diagram to the field review will help 

to locate these crashes in relation to the treatment area such that an assessment can be 

made as to whether there are factors other than pavement friction that are contributing 

to the crashes.

4) Roadway Characteristics and Confounding Factors—While many agencies 

maintain databases of roadway characteristics (shoulders, median, geometry, signage, 

etc.) a field review will help assess whether these characteristics could be contributing 

factors to the observed crashes. Confounding factors, such as driveways or 

intersections, horizontal and vertical site distances, roadside clearance, inadequate cross 

slope, and surface drainage issues can be noted as other potential contributors. The 

presence and condition of other safety countermeasures (guardrail, signage, pavement 

markings, crosswalks, etc.) should also be noted. If a high percentage of crashes are 

occurring at night, consider performing the field review at night to observe lighting 

conditions and retroreflectivity of pavement markings and warning signs. If surface 

drainage is suspected to be a contributing factor (e.g., due to inadequate cross slope, 

ponding of water, etc.), consider a field review during rainy conditions. 

5) Traffic Characteristics and Driver Behavior—While most agencies maintain traffic 

counts for their networks, these counts do not always provide the whole picture, such 

as hourly distribution and vehicle type mix. A field review scheduled to coincide with 

the timeframe of observed crash patterns may provide insight as to the impact of traffic 

characteristics on crashes. 

Additionally, observation of driver behavior may provide additional insight into potential 

causes of crashes at the site as well as information useful for the project design (e.g., 

establishment of treatment limits). Observing where vehicles begin to brake or how 

they navigate a curve, for example, may provide a better understanding of where HFST 

treatment should be applied. Observing speed differentials between posted/advisory and 

typical vehicle speeds may provide additional insight. 
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3.2 DESIGN 

Many factors can affect the cost of HFST projects. These factors should be captured in as much 

detail as practical during the design stage of an HFST project, particularly for larger projects 

with multiple installations bundled together. Below is a summary of key factors for 

consideration in HFST design. 

1) HFST Treatment Limits—Treatment limits dictate how much HFST material will be 

installed and will also impact the time necessary for installation. While there are 

anecdotal guidelines for treatment limits, the final decision for a particular site should be 

as data-driven as possible. 

• Curve Locations

o A recent survey of 26 State DOTs that use HFST for curve treatment 

revealed that nearly half of agencies select treatment limits based on a 

predetermined relationship to curve geometry, approximately one quarter 

determine treatment limits from in-person site observations, and the 

remaining States determine limits from crash diagrams, engineering judgment, 

and other factors (Wilson and Saca 2021). 

o While a common practice has been to assume treatment from the PC to PT, 

this may be overly-conservative if most crashes are occurring at a specific 

location at the middle or at one end of the curve or the other. Conversely, 

the assumption may be unconservative if crashes are occurring prior to the 

PC or beyond the PT. Many agencies have adopted policies of extending the 

treatment 100-300-ft prior to the PC and 100-300-ft beyond the PT, in 

recognition that drivers typically begin braking prior to the PC. The TTI

developed general guidelines for the distance to begin treatment prior to the 

PC based on approach speed (e.g., posted or operating) and curve advisory 

speed, as shown in table 7. 

Table 7. Recommended distance upstream of curve PC to begin HFST application 

(Brimley and Carlson 2012). 

Approach Speed 

(mph)

Curve Speed (mph)

30 35 40 45 50 55 60

35 35 - - - - - - 

40 76 41 - - - - - 

45 122 86 46 - - - - 

50 173 138 97 51 - - - 

55 230 194 154 108 57 - - 

60 292 257 216 170 119 62 - 

65 359 324 284 238 186 130 68
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o Physically locating crashes and observing driver behavior during a field review

will help with establishment of the necessary treatment limits and whether

they should begin prior to the PC, extend beyond the PT, or be limited to a

specific part of a curve.

o CPFM will help identify changes in friction leading up to, through, and away

from the curve such that agencies can adjust treatment limits based on

pavement friction. Note that CPFM provides a “map” of pavement friction,

typically at 1-ft intervals, versus locked-wheel skid tester data which only

provides a friction value for approximately 60 ft of pavement (FHWA 2021b).

o Agencies can use a curve margin of safety assessment to help establish

treatment limits based on site conditions.

• Intersection Locations

o The common practice among agencies is to treat anywhere from 200-1,000 ft

of approach to the intersection (e.g., up to the stop bar or crosswalk),

depending on where crashes are occurring. Agencies may also desire to

continue the treatment through the intersection as well as beyond the

intersection, however this is not common practice.

o Physically locating crashes, observing driver behavior (braking and stopping

behavior approaching the intersection), and monitoring traffic queues at the

intersection will help determine the length of approach that needs to be

treated and whether the intersection itself and/or the departure side of the

intersection should be treated.

o Continuous friction measurement of the intersection approach, the

intersection itself, and departure side of the intersection will help identify any

variations in friction and establish the limits of the treatment.

• Ramp Locations

o Treatment limits for curved ramps can be established using similar processes

as curve locations. Likewise, agencies can establish treatment limits for ramps

terminating at an intersection using similar processes as intersection

locations.

o Agencies may also consider additional ramp treatments (i.e., acceleration,

deceleration, and merging behavior). Physically locating crashes and observing

driver behavior during a field review will help determine the necessary

treatment limits based on these additional considerations.

• Some additional general considerations for treatment limits include: 

• Treatment of only one lane or direction. If crashes are predominantly

occurring in only one direction (e.g., on a two-lane road), or in one lane on a multi-
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lane roadway, it may not be necessary to treat both lanes or the entire roadway 

width. This is a more likely scenario at locations with significant grade where 

vehicles have a tendency to lose control going downhill rather than uphill. Crash 

data on undivided roadways may not always capture or accurately capture vehicle 

direction, and therefore agencies should make their decision based on sound data.

• Treatment of adjacent paved shoulders. While this will add additional cost to a 

project, if there is evidence from the crash data that additional friction on a paved 

shoulder would increase the likelihood of recovery from lane departure and 

decrease the likelihood of RwD, consideration can be given to treating paved 

shoulders. 

• Continuous treatment of S-curves or multiple curves. If an S-curve or 

multiple consecutive curves are to be treated, consider a continuous treatment of 

the S-curve or multiple curves, rather than leaving short areas (e.g., < 500 ft) of 

untreated pavement between them, even if crashes are not occurring in these areas. 

Changes in friction and surface appearance may alter driver behavior when such 

short areas are left untreated between treated sections. 

2) Pavement Type and Texture—Certain pavement types, such as open graded 

friction course, may need special consideration in the design process. Installation on 

open graded pavement is generally not recommended as it will require significantly more 

resin binder to fill voids in the surface, leading to a thick resin binder layer which can 

increase problems with thermal compatibility between the HFST and underlying 

pavement. Florida DOT (FDOT) does not allow installation on open graded friction 

course pavements, requiring placement of a new dense-graded asphalt prior to HFST 

installation (FDOT 2021). 

Pavement type will also impact the required surface preparation prior to HFST 

application. Shotblasting is a required surface preparation for concrete pavements in all 

known State and AASHTO specifications (AASHTO 2019). For asphalt pavements, 

shotblasting may or may not be required, depending on agency specifications. 

Pavement texture, regardless of pavement type, can have a significant impact on project 

cost as resin binder demand to achieve the desired mil thickness increases with 

macrotexture depth. If possible, measurement of macrotexture should be completed 

during a field review or using network-level texture data from pavement management 

systems. An agency can provide this information in the bidding documents so installers 

can appropriately adjust the resin binder quantities. Alternatively, an agency can specify 

the necessary resin binder coverage rate for the project based on pavement 

macrotexture so that all bidders would be estimating the correct resin binder quantity. 

The Virginia DOT, as shown in table 8, has used this approach by specifying the 

minimum resin binder application rate based on the measurement of pavement 

macrotexture depth. 
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Table 8. Virginia DOT resin binder application rate adjustment based on pavement 

macrotexture.

Macro-Texture Depth, in 

(ASTM E 965)

Minimum Resin Binder 

Application Rate, mils

<0.04 50

0.04 – 0.06 75

>0.06 2 applications @50

Note: Application rate mil thickness should be measured over a flat/smooth plate, not the 

textured surface.

3) Pavement Condition—Existing pavement condition may necessitate treatment of 

minor distresses, minor rehabilitation, or complete repaving prior to HFST installation. 

These can add significant cost to HFST projects and may be considered in the design 

stage. 

In addition to the PennDOT pavement condition guidelines shown in table 5 and table 6, 

FHWA notes the following conditions that will require minor rehabilitation or complete 

replacement (Wilson et al. 2020):

Asphalt Pavement

• Moderate-severity cracking (more than six percent of cracking in or outside the 

wheelpaths). 

• Widespread rutting greater than 0.25-inches deep. 

• Raveling. 

• Flushed or bleeding surface (typically associated with chip seals/sealcoat). 

• Areas where layer debonding or subsurface stripping is suspected. 

Concrete Pavement 

• Moderate or severe transverse cracking, longitudinal cracking, spalling, or corner 

cracking. 

• Shattered slab in more than three pieces. 

Treatment of minor distresses typically includes crack sealing prior to HFST installation, 

particularly for wider “working” cracks that may be sources for water infiltration 

beneath the HFST if not sealed.

Minor rehabilitation may include patching or small repairs of potholes, spalls, or highly 

distressed areas (if the rest of the pavement is in satisfactory condition). Minor 

rehabilitation may also include filling of ruts, depending on the pavement condition 

assessment and whether the rutting is not the result of a major structural deficiency.
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Repaving should be considered if the majority of the area to be treated is heavily 

distressed to the point that it would impact the longevity of the HFST. If repaving is 

needed, a minimum of 30 days of cure time is typically required before HFST can be 

installed over the new surface (AASHTO 2019, RTSA 2017). 

Note that consideration should be given to the potential for further pavement condition 

degradation if there will be a significant time lag (e.g., more than one year) between 

project design and construction. 

Consideration should also be given to the current pavement rehabilitation cycle for the 

site. If the site is scheduled for repaving within 1 to 2 years after HFST installation, 

consider delaying treatment until after repaving, or plan on a short re-application 

timeframe (e.g., short lifespan) for the HFST. 

4) Striping or Pavement Marking Removal and Replacement—Consideration may

be given to the cost of replacing any striping, pavement markings (e.g., arrows, lettering, 

crosswalks, etc.), and pavement markers (e.g., raised pavement markers) as this can be 

significant for thermoplastic striping/lettering or high performance tape products. While 

it is not advisable to place HFST “around” any in-lane markings, masking off lane striping 

will eliminate the need to remove and replace this striping after installation. Exceptions 

would be for installations where the treatment is to extend out into the shoulders (in 

the case of a curve or ramp) or through a crosswalk (in the case of an intersection). 

When striping removal and replacement is needed, consideration may be given to the 

cost of new striping. KYTC, for example, includes a special note in HFST project 

specifications advising contractors that multiple applications may be needed for 

waterborne striping of HFST. 

5) Maintenance of Traffic—Maintenance of traffic during installation can impact project 

cost. Agencies may consider full (e.g., detour necessary) or partial (e.g., single lane 

traffic) closures for installation, and whether closures will be limited to certain hours of 

the day or night. 

Note that restriction to nighttime installation may create potential delays in installation 

as most HFST resin binder materials are temperature-sensitive with minimum 

temperature requirements for installation.

6) Construction Staging—Agencies may also consider the practical limitations on 

staging of construction equipment and materials during installation. Rural roads with 

limited potential locations for equipment and materials staging may require the installer 

to travel miles for reloading materials into the installation vehicle. This could impact the 

length of time required for installation. Agencies should complete a general assessment 

of staging opportunities during the field review. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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CHAPTER 4—HFST MATERIALS 

HFST is a non-conventional pavement surface treatment that incorporates materials not 

commonly used by the paving industry. As such, there are requirements and considerations 

specific to the two components of HFST: surface aggregate and polymer resin binder. While the 

aggregate provides the actual skid resistance, the resin binder bonds the aggregate to the 

underlying pavement surface.

HFST systems used in the United States are considered “cold applied” systems where the resin 

binder is applied to the pavement surface first followed by broadcasting of aggregate into the 

resin binder. This is in contrast to “hot applied” systems commonly used in the United 

Kingdom where the resin binder and aggregate are mixed together and heated in a boiler at a 

high temperature to achieve a consistency that can be spread onto the pavement surface (RSTA

ADEPT 2017). 

4.1 AGGREGATE 

HFST aggregate provides the actual frictional properties for the treatment through a 

combination of microtexture and macrotexture (figure 5). Microtexture is the smaller-scale 

texture that can be thought of as the roughness of the surface of the aggregate particles. 

Microtexture contributes to friction through adhesion, or the small-scale bonding between the 

aggregate particles and vehicle tire rubber. Macrotexture is the larger, more visible texture 

created by the aggrege particles themselves and the spaces between aggregate particles. 

Macrotexture is critical for skid resistance at higher speeds and wet conditions as it provides a 

path for water to evacuate from beneath a vehicle tire, such that the tire makes contact with 

the aggregate. Macrotexture also provides the hysteresis component of friction under wet or 

dry conditions as the vehicle tire interacts with the aggregate particles (AASHTO 2008). 

Without adequate macrotexture, microtexture cannot engage vehicle tires in wet conditions at 

higher speeds, thereby reducing friction. 

While macrotexture can be measured directly through a number of different methods, 

microtexture generally cannot be measured outside of a laboratory setting. As such, 

microtexture is generally not measured directly, but assessed indirectly through friction testing 

methods and accelerated polishing tests. Because maintaining micro- and macrotexture is so 

important for pavement friction, HFST aggregate must be polish and abrasion resistant so that 

these properties are sustained under vehicle wear over the life of the treatment. 
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© Transtec 

Figure 5. Graphic. Illustration of pavement microtexture and macrotexture. 

Calcined bauxite has a decades-long proven track record of providing exceptional polish and 

abrasion resistance properties necessary for HFST. Calcined bauxite is the only aggregate 

permitted for HFST under the current AASHTO specification, virtually all State specifications, 

and in other counties with significant HFST usage, such as the United Kingdom and New 

Zealand (Highways England 2019, NZTA 2011). A 2017 article from researchers in the United 

Kingdom which reviewed 50 years of road trial data and laboratory investigation of HFST 

aggregates concluded that, “calcined bauxite is the only aggregate to consistently offer the 

highest levels of performance for the longest period of time” (Woodward and Friel 2017 p.14).

Refractory-grade calcined bauxite is raw bauxite that is calcined at temperatures of 2,900 to 

3,000°F, producing a dense, high purity, stable aggregate. Refractory-grade has a high alumina 

content (≥ 87 percent) and a very low alkali content (≤ 0.4 percent) with low impurities and a 

bulk density ≥ 3.1. 

In response to concerns over the cost of calcined bauxite and the need to import it from 

overseas, numerous laboratory and small-scale field evaluations of alternative (domestically 

sourced) aggregates have been performed (Heitzman et al. 2015; Wilson and Mukhopadhyay

2016, Heitzman and Moore 2017, Pratt 2018b, Li et al. 2017, Li et al. 2019). These evaluations 

as well as evaluation from the United Kingdom (Woodward and Friel 2017) have revealed that 

no other material provides the high level of long-term friction performance of calcined bauxite. 

It should be noted, however, that these alternative aggregates (including flint, steel slag, basalt, 

granite, emery, and taconite) may still provide satisfactory frictional properties for applications 

such as bridge deck overlays with lower friction demand. It should also be noted that there is 

now a domestic source of calcined bauxite. Other sources of refractory-grade calcined bauxite 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

41 

suitable for HFST include: China, India, and Guyana. Key physical properties of HFST aggregate 

and associated test methods include:

• Aggregate Size/Gradation—HFST aggregate has a nominal maximum aggregate size of 

3-4 mm, with most particles between 1 and 3 mm in size, as show in figure 6. Chapter 5 

provides the specific gradation required in the current AASHTO specification and most 

agency specifications. 

© The Transtec Group 

Figure 6. Photograph. Calcined bauxite aggregate for HFST. 

• Abrasion and Polish Resistance—Abrasion resistance is typically measured using the 

AASHTO T 96/ASTM C 131 Los Angeles Machine abrasion test (AASHTO 2020a). 

However, this test can be difficult to perform accurately for such a small aggregate site, and 

alternatives such as ASTM D 7428 Micro-Deval Apparatus (MDA) have been evaluated as a 

more suitable alternative (ASTM 2015a). The MDA is also known to provide some 

indication of polish resistance (Eluri 2018). Figure 7 shows an example of MDA results from 

testing of calcined bauxite versus other conventional pavement aggregates (Wilson and 

Mukhopadhyay 2016). Similar results have been reported by Heitzman et al. (2015) and Li et 

al. (2017, 2019). 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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© TTI

Figure 7. Graph. Micro-Deval loss from testing of calcined bauxite and other 

reference aggregates (Wilson and Mukhopadhyay 2016). 

Polish resistance is most commonly assessed with the ASTM D 3319 (ASTM 2017) British 

Wheel and ASTM E303 British Pendulum Tester. This test is also not well suited for such a 

small aggregate size, primarily due to difficulty in fabricating test coupons, but is currently 

specified by some agencies for lack of a suitable alternative. The NCAT Three Wheel 

Polishing Test is another option for measuring polish resistance and wear, but is more 

suitable for testing the HFST system (resin binder and aggregate) as the test is performed 

on a sample of HFST placed on a test slab (Heitzman et al. 2015). 

• Aluminum Oxide Content—Aluminum oxide (alumina) content indicates the grade of 

calcined bauxite. HFST requires refractory-grade calcined bauxite with a minimum 

aluminum oxide content of 87 percent. Testing for aluminum oxide content is performed in 

the laboratory using x-ray fluorescence spectrometry (see section 5.2.1). 

• Macrotexture—While macrotexture is a property of the HFST system and not the 

aggregate itself, it is most impacted by the aggregate and wear of the aggregate over time. 

Macrotexture is typically assessed with a volumetric technique such as ASTM E965 (ASTM 

2019b) to compute mean texture depth (MTD) or using laser-based measurement to 

compute a mean profile depth (MPD) in accordance with ASTM E1845 (ASTM 2015b). In 

general, HFST should maintain an MPD or MTD of at least 1.0 over the life of the 

treatment. 

• Microtexture—Currently aggregate microtexture can only be measured and fully 

characterized directly in the laboratory using specialty laser surface scanning equipment. 

However, agencies can use friction tests in a laboratory such as the ASTM E303 British 

Pendulum Tester (ASTM 2018b) and ASTM E 1911 Dynamic Friction Tester (ASTM 2019a) 

as surrogate measures of microtexture. 

• Cleanliness—Cleanliness of HFST aggregate is critical for HFST performance. Cleanliness 

includes contaminants in the aggregate stockpile as well as cleanliness (e.g., dust content) of 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

43 

the aggregates themselves. Currently, only subjective assessment is used to determine 

aggregate cleanliness.

4.2 RESIN BINDER

The polymer resin binder bonds the aggregate particles to the underlying pavement surface. As 

such, it must be compatible with both the aggregate and the underlying pavement surface and

must be able to securely hold the aggregate in place under high shear stresses from traffic 

under a potentially wide range of temperatures over the life of the treatment. 

The most common resin binder materials for HFST in the United States are epoxy resin and 

polyester resin, although agencies have used methyl methacrylate (MMA) on a very limited 

basis. These multi-component, thermosetting, exothermic resin binders are considered high 

strength, low modulus materials that are chemical and ultraviolet light resistant and moisture 

sensitive during curing. 

Epoxy Resin is the most commonly used HFST resin binder in the United States. Epoxy resin is 

typically a two-component system (commonly mixed at a 1:1 ratio by volume) with one 

component being a resin with a portion of dilutants or other proprietary ingredients (to 

achieve specified material properties), and the other component being the curing agent or 

hardener (de Leon Izeppi et al. 2010). Epoxy resin is a thermosetting material which cures 

under an exothermic reaction. As such there are minimum temperature requirements for using 

epoxy resin, typically 50°F and above. Cure times can be adjusted (per manufacturer 

recommendations) to account for higher or lower temperature conditions.

Agencies across the United States have also used polyester resin for HFST. Polyester resin is a 

two-component material (although mixed at a much different ratio than epoxy resin) but an 

accelerator can also be added to shorten cure time. The primary advantage of this material is 

that it can cure under a wide range of temperatures (below 40°F), which is beneficial for cooler 

weather installations. 

Other resin binders that have been used internationally (for hot applied systems in particular) 

but are not common in the United States are polyurethane resin, acrylic resin, and rosin ester. 

Key physical properties for the resin binder which will affect installation and performance of the 

finished surface include:

• Viscosity—Viscosity is a measure of resistance to flow or how “thick” or “thin” the resin 

binder is. Viscosity affects how the material flows when deposited and spread onto the 

pavement surface. Lower viscosity resin binder will more readily flow down into the pore 

structure of the pavement, however, it also tends to run across superelevation or down 

pavement grade if the aggregate is not applied immediately after the resin binder to help 

hold it in place. Higher viscosity resin binder may not blend as easily or spread as easily,

potentially leaving a non-uniform or uneven surface. It will also not penetrate the pavement 

pore structure as well and may resist penetration of aggregate when broadcast onto the 

resin binder. 
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While requirements for viscosity are outlined in agency specifications, these requirements 

are for laboratory conditions (standard temperature). During installation, resin binder 

viscosity is highly affected by ambient and pavement temperatures. In general, the warmer 

the temperature, the lower the viscosity, although resin binder manufacturers may be able 

to adjust these properties by varying component proportions. Conversely, the cooler the 

temperature, the higher the viscosity, unless the manufacturer provides recommendations 

to adjust proportioning to account for cooler temperatures. Resin binder manufacturer 

recommendations for material temperatures and proportioning should always be followed 

very carefully based on ambient and surface temperatures during installation and the 

equipment used to apply resin binder to the pavement surface. 

The effect of temperature on resin binder viscosity and associated “drain down” (i.e., how 

quickly the resin binder drains down into the pavement pore structure) was measured in 

the laboratory by researchers from TTI, and is illustrated in figure 8 (Wilson and 

Mukhopadhyay 2016). Researchers observed that for the same asphalt pavement surface 

(FC-5), resin binder film thickness decreased much quicker at higher temperature (95°F) 

than at moderate temperatures (65-72°F) Note however that for an actual HFST 

installation, application of aggregate immediately after the resin binder causes a capillary rise 

or wicking action that can easily offset this drain down. 

© TTI

Figure 8. Graph. Impact of pavement temperature and resin binder viscosity on 

resin binder film thickness due to drain down (Wilson and Mukhopadhyay 2016). 

• Gel Time—Thin-film gel time is the time from the application of the liquid material onto 

the pavement surface until it begins to thicken (gel) and no longer flows. Gel time affects 

the amount of time available to spread the resin binder on the pavement surface, and more 

importantly, the amount of time before aggregate must be broadcast onto the resin binder. 

As resin binder materials begin to gel, they will resist penetration of the aggregate, which 
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can lead to aggregates not fully embedded in the resin binder. Like viscosity, gel time is 

highly affected by temperature for most resin binder materials and installers should always 

refer to resin binder manufacturer recommendations regarding gel time. 

• Cure Rate—Cure rate is how quickly the resin binder material cures or hardens to the 

point that excess aggregate can be swept and the surface can be opened to traffic. Note 

that cure time for sweeping will likely be different from that for opening to traffic. While 

there is generally not a problem with resin binder curing quickly (assuming aggregates are 

broadcast onto the surface before gel), a slower cure rate will delay sweeping and opening 

to traffic. Similar to viscosity and gel time, cure rate is highly dependent up on temperature. 

In general, the warmer the temperature, the shorter the cure time. Resin binder 

manufacturers provide guidance for the cure time of their product, typically based on 

temperature, similar to the product label shown in table 9. 

Table 9. Resin binder product label showing minimum curing time based on 

temperature. 

Average Temperature Cure Time (hours)

60-64°F (16-18°C) 5-6 

65-69°F (19-21°C) 5 

70-74°F (22-23°C) 4 

75-79°F (24-26°C) 3 

80-84°F (27-29°C) 3 

85+°F (29+°C) 3 

• Adhesion—Adhesion is a measure of how well the resin binder adheres to the underlying 

pavement surface. The most common test for adhesion is the ASTM C1583 pull-off tensile 

strength test (2020c). This test is not commonly specified for HFST acceptance in the field 

due to the destructive and specialized nature of the test, however, a few agencies require 

the test for acceptance of the resin binder based on laboratory testing (Wilson and Saca

2021). It should be noted, however, that because the test method is designed for concrete, 

the 100 percent substrate mode of failure will vary when performed on an asphalt 

pavement. 

• Thermal Compatibility—Thermal compatibility is a measure of how well the resin 

binder remains bonded to the underlying pavement surface under temperature cycling. 

Thermal compatibility considers the difference in the coefficient of thermal expansion (CTE) 

between the HFST and underlying pavement surface. In general, the greater the difference in 

the coefficient of thermal expansion between the HFST and underlying pavement, the higher 

the shear stresses at the HFST-pavement interface or within the underlying pavement, 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

46 

which can lead to delamination or cohesive failure within the pavement itself. Despite large 

differences in CTE between HFST and concrete/asphalt surfaces, failure due to thermal 

compatibility issues generally only occurs when the HFST is placed too thick (i.e., due to 

high pavement porosity) or when HFST is placed over a weak asphalt pavement. While 

laboratory testing of this property is included in many agency specifications (in accordance 

with ASTM C884), the test protocol calls for placement of the resin binder over a concrete 

substrate, which may not be representative of placement over asphalt surface (ASTM 2016). 

The Nevada DOT is currently investigating thermal compatibility and developing 

appropriate specifications (Nevada DOT n.d.). 

While it is ultimately the installer’s decision on which resin binder to use (assuming it meets 

agency specification requirements), resin binder selection based on the specifics of a given 

project is critical. Resin binder should be appropriate (or appropriately proportioned) for:

• Site Conditions—Site conditions include pavement type (specifically pavement texture 

and/or porosity), roadway cross-slope/superelevation, and grade. 

• Installation Conditions—Installation Conditions include the ambient and pavement 

temperature during installation (with consideration given to nighttime vs. daytime 

installation) and lane closure restrictions/opening to traffic requirements. 

• Installation Methods—Installation methods are the equipment for blending and 

applying the resin binder. This also includes equipment and timing of aggregate 

placement. 
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CHAPTER 5—SPECIFICATIONS AND INSTALLATION 

This chapter discusses specifications and installation considerations for HFST. The list below 

summarizes key factors based on lessons learned from early implementation and agencies with 

mature HFST programs. 

5.1 KEY COMPONENTS OF HFST INSTALLATION 

The following are key components of an HFST installation which agencies should cover through

HFST specifications, a quality control plan (QCP), and inspection practices, and will be 

discussed in greater detail throughout this Chapter. 

• Material Handling and Testing—As non-conventional materials, there are special 

considerations for handling and testing of HFST resin binder and aggregate materials. 

o Resin binder component material storage in accordance with manufacturer 

recommendations. 

o Aggregate material storage to keep the material clean and dry. 

o Verification that the materials for use on-site are approved for use and the same 

as those called for by the installer in the QCP. 

o Verification testing of materials, if required by the agency, in lieu of or in addition 

to certified test results from the installer. 

o Staging of materials in advance of and during installation to help prevent delays 

during installation for refilling installation vehicles.

• Surface Preparation—Preparation of the underlying pavement surface is critical for 

the installation and long-term performance of HFST. Key aspects of surface preparation 

include: 

o Pavement repairs—patching of distressed areas, removal of rutting, sealing 

and/or filling of wide (working) cracks. 

o Striping and pavement marking—removal or masking of striping and pavement 

markings as required. 

o Cleaning and roughening—processes used to thoroughly clean and roughen the 

pavement surface to help ensure bond between the resin binder and pavement 

surface. 

o Protection of joints and drainage structures—protection of working joints (e.g., 

concrete pavement or at bridge abutments) and drainage inlets to prevent 

intrusion of HFST materials during installation. 
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• Application Methods and Equipment—Methods and equipment for metering, 

blending, and applying the resin binder, and processes and equipment for applying the 

aggregate. 

• Aggregate Removal and Reclamation—Removal of excess aggregate and

requirements for reclamation, if permitted. 

• Preparation for Opening to Traffic—Final inspection and preparation of the 

finished surface for opening to traffic, including replacement of striping. 

• Acceptance Testing—Acceptance testing typically consists of friction testing after 

opening to traffic to give the surface an initial wear-in period (typically 30 to 60 days 

after opening to traffic), but may also include macrotexture testing and bond testing, 

depending on agency requirements. 

• Early-Age Monitoring—Monitoring the treatment over the first few days and weeks 

after opening to traffic will help identify any potential materials and workmanship-related 

issues. Monitoring should also include a re-sweep of the treated area and adjacent lanes 

or shoulders to remove aggregate that is naturally shed under traffic wear during the 

first few weeks. 

5.2 HFST SPECIFICATIONS

AASHTO MP 41-19 Standard Specification for High Friction Surface Treatment for Asphalt and 

Concrete Pavements Using Calcined Bauxite is the current version of the AASHTO specification 

for HFST developed through an agency-industry consensus process (AASHTO 2019). This 

specification is intended to provide guidance to agencies seeking to develop their own 

specification but can also be used as-is by agencies. Agencies with mature HFST programs have 

developed their own specifications with agency-specific requirements for materials and 

installation practices. Highlighted below are key elements of an HFST specification based on the 

AASHTO specification and other agency specifications. Specific requirements (e.g., resin binder 

physical properties) from the current AASHTO specification are shown, but not those from 

other agencies as there is a wide range of variations. (Note that the AASHTO specification is 

currently being revised and split into two specifications, one for materials and one for installation).

5.2.1 PHYSICAL PROPERTY REQUIREMENTS FOR MATERIALS

• Many agencies require pre-approval of resin binder and aggregate materials before use on a 

project. Qualified product lists (QPLs) help ensure that only materials meeting specification 

requirements will be used on the project without the need to test the material ahead of 

installation (unless project-level verification tests are required). As part of pre-approval, 

agencies may also require that HFST products be evaluated through the AASHTO National 

Transportation Product Evaluation Program (NTPEP) for High Friction and Thin Overlays 

(AASHTO n.d.). Tennessee DOT, for example, has a QPL for HFST, and part of the preapproval process is conformance with the AASHTO HFST specification requirements for 
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49 

resin binder and submission of test data from an AASHTO NTPEP evaluation (Tennessee 

DOT 2021a, Tennessee DOT 2021b).

• Agencies may also allow material suppliers to submit a certification that materials meet the 

specified requirements in lieu of separate testing by the installer or agency prior to 

construction. The certification includes independent laboratory test results that satisfy 

agency specification requirements. 

Physical requirements for polymer resin materials may include some or all of those shown in 

table 10, depending on the agency. Note that many agencies have their own test methods for 

these properties. The AASHTO specification and several agency specifications provide separate 

requirements for epoxy, polyester, and MMA resin binders.

Table 10. Physical property requirements for HFST resin binder materials. 

Resin Binder 

Property

AASHTO/ASTM Test 

Method

AASHTO Specification 

Requirement

Viscosity

ASTM D2556 

(spindle and speed selection 

based on ASTM D2556-11)

1,000 cP min. (epoxy and polyester)

1,500-2,500 cP min. (MMA)

Flash Point ASTM D3278 

(see Note 3 of D3278)

See Safety Data Sheet (SDS)

Gel Time ASTM C881/AASHTO M235 10 minutes min (epoxy and polyester) 

15 minutes min (MMA)

Compressive 

Modulus ASTM D695 130,000 psi max. @ 7 days (epoxy and MMA)

Compressive 

Strength 

ASTM C579 

(Test Method B for epoxy and 

polyester)

1,000 psi min. @ 3 hr., 3,000 psi min. @ 24 

hr. (epoxy and polyester)

1,500-3,000 psi @ 7 days (MMA)

Tensile Strength ASTM D638 Type I

2,000-5,000 psi @ 7 days (epoxy and 

polyester)

500-1,000 psi @7 days (MMA)

Tensile Elongation ASTM D638 Type I 30% min. (epoxy and polyester)

50% min. (MMA)

Absorption ASTM D570 1% max. 

Type D Hardness

ASTM D2240

(cure specimen for 

7 days ± 6 hr.)

60-80 (epoxy and polyester) 

50-60 (MMA)

Thermal 

Compatibility ASTM C884 PASS

Infrared Spectrum ASTM E573/Section 7.1.11 Combined & Components

Cure Rate (at 75°F) ASTM D1640 Typical: 3 hours max.

Not Included in AASHTO 

Adhesive Strength 

(at 24 hours) ASTM C1583 Typical: 250 psi min. or 100% substrate failureNot Included in AASHTO

Chloride 

Permeability AASHTO T 277 Typical: < 100 coulombs @ 28 daysNot Included in AASHTO

• Based on discussions with resin binder manufacturers, Wilson and Saca noted that current 

resin binder specifications place too much emphasis on high strength and high modulus 

criteria, when the focus should be on toughness or resilience. The resin binder should hold 

the aggregate well and adhere to the underlying pavement well, but also be as flexible as 
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possible (Wilson and Saca 2021). Ongoing research by Nevada DOT should help with 

refinement of specifications for this purpose (Nevada DOT n.d.). 

Physical requirements for aggregate materials may include some or all of those shown in table 

11, depending on the agency. 

Table 11. Physical property requirements for HFST aggregate materials.

Aggregate Property AASHTO/ASTM 

Test Method

AASHTO Specification 

Requirement

Los Angeles Abrasion (LAA) AASHTO T 96

(Grading D) 20% max.

MDA ASTM D 7428 5% max.

British Wheel ASTM D3319

AASHTO T 279

Typical: 38 min.

Not Included in AASHTO

Aluminum Oxide ASTM E 1621 87±2%

Gradation AASHTO T 27

No. 4 sieve: 100% passing

No. 6 sieve: 95-100% passing

No. 16 sieve: 0-5% passing

No. 30 sieve: 0-0.2% passing

Soundness AASHTO T104 Typical: 12-15% max.

Not Included in AASHTO

Moisture Content AASHT T255 0.2% max.

• Note that the LAA test method is marginally appropriate for HFST due to the small-size 

aggregate which will require a substantial sample size to achieve the requirements for 

Grading D. Some agencies require this test to be performed on the parent aggregate (e.g., 

larger size before crushing). 

• The MDA test has been noted to provide an indication of both abrasion and polish 

resistance and therefore some agencies only require this test and not a separate polishing 

test. MDA is more appropriate for smaller aggregates (even though HFST gradation is still 

marginal for the standard) than LAA. It is possible that modifications to ASTM D7428 

(ASTM 2015a) will be developed for testing HFST aggregates. 

• Aluminum oxide content reflects the hardness of the aggregate. Some have questioned the 

87 percent aluminum oxide content and whether a lower grade would still provide the 

desired performance. There is currently not enough data to justify a lower requirement, 

although at least one State (FDOT) has lowered their requirement to 86 percent, and the 

next revision of the AASHTO specification will set this as 85 percent minimum 

• FDOT is also exploring an alternative method of X-ray fluorescence for measuring 

aluminum oxide content using ASTM C 1271 (ASTM 2020d), but this has not yet been 

adopted into practice (Wilson and Saca 2021). ASTM E1621, “Standard Guide for Elemental 

Analysis by Wavelength Dispersive X-Ray Fluorescence Spectrometry” (ASTM 2021) is 

currently being considered for the AASHTO HFST specification. 

• Research from Indiana DOT reported that specific gravity and water absorption may 

indicate if the raw bauxite is fully calcined, which may be another indicator of the quality of 
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51 

the material (Li et al. 2017. However, this has not been confirmed through further 

investigation.

• Freeze-thaw soundness, in accordance with AASHTO T 103, has been specified in at least 

one agency specification, but is not common and not included in the AASHTO specification. 

5.2.2 QUALIFICATIONS OF THE INSTALLER 

Many agency specifications require that the installer have prior experience with HFST 

installation and submit proof of prior experience for a specified minimum number of projects 

or SY of HFST installation. Proof of prior experience may permit an installer to forgo 

installation of a test strip (described below). The AASHTO specification calls for a minimum of 

three projects with a cumulative minimum of 10,000 SY of HFST in the past 3 years, and 

documentation of friction numbers from those projects (AASHTO 2019). 

5.2.3 QUALITY CONTROL PLANS

QCPs require the installer detail every aspect of their plan for installation of HFST. QCPs, 

which must be approved by the agency, allow the agency to provide input on various aspects of 

the installation before construction begins, and allows the agency to hold an installer 

accountable for practices outlined in the plan. While not exhaustive, key items commonly found 

in QCPs include:

• Identification of a Plan Administrator or Project Superintendent who has full authority 

to institute any action necessary for the successful operation of the plan, and other key 

personnel, such as an on-site Lead Technician. 

• Documentation of resin binder and aggregate sources and materials certifications. 

• Procedures for storage of stockpiled and on-site materials. 

• Plan for on-site representation by the resin binder material supplier during initial 

installation. 

• Proposed methods for surface preparation (distress treatment, striping/pavement 

marking treatment, cleaning/roughening, sweeping, etc.). 

• Plan for documenting material quantities used for verification of application rate of resin 

binder and aggregate. 

• Moisture control methods for aggregate. 

• Procedures and equipment to be used for: resin binder proportioning, blending, and 

application; aggregate application and removal. 

• Equipment calibration records for all metering and application monitoring devices. 

• Plan for monitoring and recording of ambient conditions (air temperature, surface 

temperature, relative humidity). 

• Plan for corrective actions for unsatisfactory construction practices and deviations from 

project specifications. 

• Sampling and testing plan for acceptance. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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• Methods for determination of time for sweeping and opening to traffic. 

• Plan for replacement of pavement markings. 

5.2.4 APPLICATION REQUIREMENTS

Most agencies currently require fully-automated continuous application installation methods

capable of covering a full lane width in a single pass in their specifications (Wilson and Saca

2021). The purpose for this requirement is to help ensure consistency and uniformity of the 

finished surface through accurate proportioning, thorough blending, and uniform application of 

resin binder and aggregate materials. A recent survey of 26 States with HFST programs 

revealed that approximately 70 percent had problems with manual application often or 

sometimes versus only 30 percent with fully-automated application (Wilson and Saca 2021). In 

addition to requiring fully-automated application, Delaware DOT and West Virginia DOT 

further require real time data reporting of installation information, including resin binder 

quantity and thickness, aggregate quantity, and ambient temperatures. Agencies which require 

fully automated installation will also permit manual installation methods for smaller and/or 

irregular areas/lane widths, typically less than 200-300 SY, where automated installation is not 

practical. 

Many agencies also specify requirements for the timing and method of aggregate application. 

Georgia DOT, for example, limits the height from which aggregate can be dropped onto the 

resin binder to 24 inches, while Illinois DOT, West Virginia DOT, and Delaware DOT limit this 

to 12 inches. Tennessee DOT and Caltrans require aggregate to be applied within 3 minutes 

after placement of the resin binder, while KYTC specifies within 2 minutes; FDOT and 

Delaware DOT require application within 30 seconds, and West Virginia DOT requires 

application within 3 seconds. The purpose of these requirements is to ensure that the resin 

binder is not displaced when the aggregate is applied and to confirm that the aggregate is 

applied well within the gel time of the resin binder. 

Agencies typically specify limitations on application temperatures, depending on material 

requirements. As noted in chapter 4, epoxy resin binders will typically not cure (or cure very 

slowly) below 50°F, and most resin binders will gel too quickly at higher temperatures (e.g., 

above 100°F). Typical temperature limitations are a minimum of 50°F surface temperature and 

maximum of 110°F ambient temperature, but as noted in chapter 4, this is highly dependent on 

the limitations of the particular resin binder that is used. Most agencies will allow placement 

outside of these limits if permitted by the manufacturer. Installation over wet or damp surfaces 

is always prohibited, with some agencies requiring a moisture test such as ASTM D 4263, 

“Indicating Moisture in Concrete by the Plastic Sheet Method” (ASTM 2018a) at the discretion 

of the engineer if surface moisture is questionable. Many agencies further restrict installation 

when there is more than a 50-percent probability of rain in the forecast. 
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5.2.5 APPLICATION RATE 

For resin binder application rate, the goal is to achieve a thickness that will provide 

approximately 50-percent embedment of the aggregate particles, as illustrated in figure 9. If the 

resin binder layer is too thin, aggregate particles are more likely to ravel or pull out of the resin 

binder under traffic wear. If the resin binder layer is too thick, resin binder material is wasted, 

and the finished surface will not have the desired macrotexture to ensure the frictional 

properties. 

© FDOT

Figure 9. Graphic. Illustration of aggregate embedment in resin binder layer 

(FDOT 2021). 

Agencies typically specify a minimum resin binder mil thickness of 50-65 mils. This is the 

thickness of resin binder required to achieve approximately 50 percent embedment of a 3-4 

mm sized HFST aggregate over a perfectly smooth and flat surface. Accounting for displacement 

of resin binder by the aggregate particles, this mil thickness should still provide the 50 percent 

embedment over typical pavement textures. As discussed in Chapter 3, however, the coverage 

rate (e.g., gallons per SY) required to achieve 50 percent embedment is highly dependent on 

the level of macrotexture in the underlying pavement. To account for this Virginia DOT, for 

example, adjusts the required mil thickness based on pavement macrotexture depth (table 8) 

from which the installer can determine the necessary coverage rate. Agencies can use figure 10 

and figure 11 to estimate the required coverage rate based on the desired resin binder mil 

thickness. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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Figure 10. Equation. Calculation of coverage rate in gallons per square yard based 

on mil thickness. 

 

Figure 11. Equation. Calculation of coverage rate as SY per gallon based on mil 

thickness

Verification of mil thickness during installation using a wet film thickness gage can be very 

difficult, particularly on coarse textured pavements. For this reason, agencies should compare 

actual material usage to the required coverage rate to achieve the desired mil thickness for the 

pavement texture as part of inspection. Louisiana DOTD, for example, requires the installer to 

report the quantity of materials used per unit area (e.g., 1,000-ft sections), along with 

measurements of mil thickness obtained during installation. 

Aggregate application rate is typically specified as 12-15 lb/SY or “to refusal” as additional 

aggregate may be necessary to completely cover all resin binder. This application rate varies 

slightly by agency with ranges from 11 to 20 lb/SY. Automated aggregate application processes 

tend to be more efficient in optimizing material usage than manual processes, and therefore 

actual material usage may vary from this range. The main concern is that all resin binder is 

completely covered by aggregate, similar to that shown in figure 12. 

© The Transtec Group

Figure 12. Photograph. Example of a uniform application of aggregate with no resin 

binder visible. 
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5.2.6 TEST SECTIONS

Most agencies require installers to complete an initial test section before beginning full-scale 

production application. The purpose of a test section is for the installer to demonstrate 

competence in HFST placement and to verify that the installed surface meets agency acceptance 

requirements (e.g., friction and texture) and can be opened to traffic on schedule. Test section 

requirements vary widely but are typically at least one lane wide by 20 to 200 ft in length. Most 

agencies will allow the test section to be placed as part of the actual site location and left in 

place if it meets acceptance criteria. For large projects with multiple installation locations, the 

test section is typically only required for the first installation. 

5.2.7 SURFACE PREPARATION

Typical minimum surface preparation requirements for cleaning and roughening of the 

underlying pavement include:

• Asphalt/Bituminous Surfaces—air wash with a minimum 180 cubic feet/minute of 

clean and dry compressed air. Agencies may also require shotblasting of bituminous 

surfaces to remove bleeding/flushing (on seal coat/chip seal surfaces, in particular) fog 

seal, or to open up the pore structure on a dense-graded asphalt surface, but this should 

be followed by a compressed air wash. 

• Concrete Surfaces—shotblasting to a minimum concrete surface profile (CSP) of 5 

but no more than 7 (Winkler 2014). Shotblasting should always be followed with an air 

wash (similar to asphalt surface requirements) to ensure all latent dust from the 

shotblasting process has been removed. 

Agency requirements vary on treatment of distresses prior to HFST application. In general, 

highly distressed pavements should be removed and replaced prior to HFST installation to 

ensure long-term performance. However, if there are budget limitations and a shorter HFST 

lifespan can be tolerated for the sake of an immediate safety improvement, HFST can still be 

placed, though this is not recommended. Agencies can remove minor rutting and seal wider 

working cracks using crack sealant materials that are compatible with HFST resin binder. Note 

that crack sealant should be kept below the top of pavement surface and not overbanded onto 

the pavement surface. Most agencies specify that cracks wider and deeper than 0.25 inches be 

pre-treated with HFST resin binder or binder/aggregate slurry just prior to HFST placement. 

Agencies can also mask off joints in concrete pavements, as well as bridge approach joints. 

Drainage inlets and manhole covers should also be covered. 

If repaving is required prior to HFST installation, most agencies require a 30-day cure period 

for both asphalt or concrete pavements prior to application of HFST. 

Most agencies require removal of any in-lane pavement markings, particularly if they are 

thermoplastic as HFST will not bond well to these. Raised or recessed pavement markers can 

be masked off to reduce the cost of replacement, at the discretion of the agency. Whether 

striping can be masked off or must be removed and replaced is at the discretion of the agency. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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In general, lane-dividing striping should be removed and replaced so that HFST is uniform 

across the width of the roadway, but shoulder striping can be masked if HFST will not be placed 

out into paved shoulders, at the discretion of the agency. KYTC adds a note to project plans 

indicating that multiple lifts of paint may be required (particularly for waterborne paint) over 

HFST when replacing striping to ensure the installer accounts for this in their estimate. 

5.2.8 AGGREGATE REMOVAL, RECLAMATION, AND RE-SWEEPING 

Most agencies require removal of excess aggregate (after the HFST has cured) using a vacuum 

truck or power broom at the discretion of the installer. Requirements for aggregate removal 

are that the resin binder is adequately cured before beginning removal and that all loose 

material is removed prior to opening to traffic. Some agencies will allow excess aggregate to be 

swept from the edge of the roadway onto native shoulders on rural roadways, but in an urban 

environment or when paved shoulders are present, vacuum sweeping is generally necessary. 

Many agencies do not permit the reuse of aggregate recovered from a previous placement. 

Reclaimed aggregate tends to have a different gradation (i.e., finer gradation) from virgin 

material and may also have significant dust content from the vacuuming process used to 

recover it. Agencies which do permit reclaimed aggregate to be used require that it be remixed 

with virgin aggregate at a minimum ratio of two (or three) parts of virgin material to one part 

reclaimed aggregate. 

Because HFST naturally sheds aggregate under traffic wear during the first few days and weeks 

after initial installation, most agencies require re-sweeping of the surface within 30 days after 

installation. Shed aggregate tends to accumulate on the edges of a lane and on paved shoulders 

or adjacent lanes, which can create a safety hazard if not removed through re-sweeping. 

5.2.9 ACCEPTANCE AND OPENING TO TRAFFIC REQUIREMENTS

Typical acceptance criteria include a subjective assessment of the finished surface to ensure all 

resin binder has cured and all loose aggregate has been removed, friction testing, and for a few 

agencies, macrotexture testing. 

Friction testing should be performed sometime after the surface has been opened to traffic to 

allow a wear-in period as friction values immediately after installation may be artificially high. 

Friction testing is typically performed with an ASTM E 274/AASHTO T 242 locked-wheel skid 

tester (LWST) (ASTM, 2020b, AASHTO 2018b) or ASTM E1911 Dynamic Friction Tester 

(DFT) (ASTM 2019a). From a recent survey of State DOTs with HFST programs, 

approximately two-thirds require LWST testing, approximately one quarter require DFT 

testing, and less than 10 percent require other methods (Wilson and Saca 2021). 

• LWST testing is typically performed using either an ASTM E501 ribbed tire (AASHTO, 

KY, LA, WV, TX, TN, IL, FL, MO) or ASTM E524 smooth tread tire (PA, VA), 

depending on agency standard practices. Testing is typically performed and reported at 

40 mph, but speed corrections can be used if it is necessary to test at a lower speed due 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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to roadway geometry or traffic conditions. The number of LWST tests will depend on 

the length of the treatment, with 1 to 3 tests typically required. For shorter sections, 

this may require multiple passes with the LWST. The AASHTO specification requires 

FN40R = 65 for acceptance, while agency-specific values range from FN40R of 65-75 

and FN40S of 55-70. 

• The DFT is a stationary test device requiring a lane closure to perform the test. Many 

agencies specify this test in lieu of the LWST due to concerns with safety and the 

validity of LWST measurements on sharp curves. The DFT provides a friction reading 

over a range of speeds from the specified test speed (typically 80 kph) down to 0 kph. 

Most agencies require reporting of the friction value at 60 kph or 20 kph. The number 

of test locations is variable with some agencies requiring only one test per location and 

others requiring testing as frequently as every 200 ft. The AASHTO specification does 

not provide a friction requirement based on DFT testing. Agency-specific values range 

from DFT(60 kph) of 0.75 to 0.90. 

Agency requirements for timing of initial friction testing range from immediately after 

installation to 90 days after installation, with many agencies requiring additional testing 

anywhere from 90 days to 12 months after installation. Some agencies will allow for a reduced 

pay factor for a lower initial friction value rather than requiring removal and replacement. 

PennDOT, for example, requires FN40S = 70 for full payment, reduces payment to 90 percent 

for FN40S of 65-69, and requires removal and replacement below FN40S of 65. 

Several agencies (DE, IL, IN, LA, MD, NC, TN, and VA) require macrotexture testing in 

addition to friction testing. Macrotexture testing is typically specified as the mean texture depth 

(MTD) in mm based on the ASTM E 965 volumetric method (ASTM 2019b) or as MPD in mm, 

based on the ASTM E2157 circular track meter device. The acceptance requirement for 

macrotexture (whether MTD or MPD) is typically a minimum 1.0 mm. 

5.2.10 WARRANTY AND PERFORMANCE GUARANTEES 

Warranties and performance guarantees are not common practice for HFST in the United 

States. However, a few agencies include some form of these (typically for a one-year

performance period) in their specifications which require the installer to address early-age 

performance issues that could be related to materials and workmanship. 

• FDOT requires a one-year warranty period against loss of friction below the acceptance 

threshold (FN40R = 65) and latent surface defects. These defects, which require 

remedial work if more than 10 percent of any given 100 SY of HFST application area, 

include (FDOT 2017):

o Surface cracking (Class 1B or greater)—requires removal and replacement of 

distressed areas to the full distressed depth and to a minimum surface area of 150 

percent of each distressed area.
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o Raveling and/or Delamination—requires grinding and replacement of distressed 

areas to the full distressed depth and to a minimum surface area of 150 percent of 

each distressed area.

o Soft Spots/Bleeding—requires grinding and replacement of distressed areas to the 

full distressed depth and to a minimum surface area of 150 percent of each 

distressed area.

• Delaware DOT includes a one-year warranty against surface defects, although specific 

defects are not identified. 

• Louisiana DOTD requires a performance guarantee with performance measures 

including: skid resistance and delaminations or more than 50-percent aggregate loss on 

more than 0.1 percent of installation area or on more than 10 contiguous ft2 of overlay 

area. 

Longer warranty periods are more common for HFST internationally. 

• Highways England specifies a two-year performance guarantee to address the following 

performance criteria: skid resistance, erosion index, overall system loss, fatting-up, 

texture depth, cracking, tensile adhesion, scuffing test, and visual assessment (Highways 

England 2019, BBA 2017). 

• The New Zealand Transport Agency (NZTA) specifies a two-year performance 

guarantee which covers: skid resistance, macrotexture, binder and aggregate 

retention/loss, visual appearance, and loose aggregate (NZTA 2011).

5.2.11 INSTALLATION AND INSPECTION TRAINING 

Many agencies require the installer to schedule training for project inspectors and installer 

personnel in advance of the actual installation. The purpose of the training is to provide an 

overview of the installation process and highlight key items for inspection as HFST materials 

and installation practices are different from traditional paving or surface treatments. Currently 

the American Traffic Safety Services Association (ATSSA) provides a comprehensive HFST 

inspection and installation training course (ATSSA n.d.), FHWA also offers a training course, 

and a few agencies may have their own training. 

5.3 APPLICATION METHODS

The two primary methods for HFST application are fully-automated and manual methods. As 

noted previously, most agencies require fully-automated HFST installation, with manual 

application permitted for smaller or irregular areas (less than 200-300 SY) where automated 

installation is impractical. Installations where lane width varies over the treatment section (e.g., 

ramps which may vary from 12 ft at the ends to 14-15 ft in the middle) or irregular areas at 

tapers or turn pockets are examples where manual application may need to supplement 

automated installation.
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5.3.1 MANUAL APPLICATION

Manual application consists substantially of manual processes for resin binder proportioning, 

resin binder blending, resin binder application, and aggregate application. While manual 

installations may utilize components, such as automated proportioning and blending of resin 

binder or mechanically-assisted placement of aggregate, application of the resin binder is 

typically performed with manual labor using notched squeegees to spread the resin binder on 

the pavement surface, as shown in figure 13. Aggregate placement, whether broadcast manually 

(figure 14) or with mechanically-assisted methods such as venturi blowers (figure 15) typically 

lags several minutes behind resin binder application. Additional detail on the various 

components of manual application are provided in chapter 6. 

© The Transtec Group

Figure 13. Photograph. Example of mechanically-assisted manual resin binder 

application.
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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© The Transtec Group

Figure 14. Photograph. Example of manual application of aggregate, broadcast by 

hand.

© FHWA

Figure 15. Photograph. Example of mechanically-assisted manual aggregate 

application using a venturi blower.

5.3.2 FULLY-AUTOMATED APPLICATION

While there is no formal definition of fully-automated application, in general terms it consists of 

a single vehicle which is capable of placing HFST in a single pass with minimal manual effort. All 

materials are contained on the vehicle, and automated systems for conditioning (pre-heating), 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

61 

metering, blending, and placing the resin binder and aggregate materials are utilized for 

application of HFST. These vehicles allow for on-the-fly adjustment of resin binder thickness 

and aggregate application rate. They are typically set up for a fixed width at the beginning of a 

placement and can usually place 2,000-3,000 SY of HFST before refilling materials. Only a 

minimal (e.g., 2-3 person) crew is typically necessary to operate these vehicles, and they are 

capable of installing HFST at a rate of 40-50 ft per minute (or more), one lane wide. Most 

modern, fully-automated vehicles automatically track material usage and provide this 

information in real-time during installation. Figure 16 shows an example of a fully-automated 

installation vehicle and figure 17 shows a closeup of the resin binder and aggregate placement 

for a fully-automated installation vehicle. Additional information on fully-automated application 

is provided in chapter 6. 

© The Trasntec Group 

Figure 16. Photograph. Example of a fully-automated installation vehicle.
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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© The Transtec Group

Figure 17. Photograph. Example of resin binder and aggregate placement on a 

fully-automated installation vehicle.

5.3.3 COMPARISON OF APPLICATION METHODS

Table 12 highlights some of the key advantages and disadvantages of manual and fully-automated 

application methods. When it comes to HFST installation, the most critical elements affecting 

HFST performance are: ensuring that the resin binder is properly conditioned and

proportioned (to manufacturer recommendations), confirming it is thoroughly blended and 

placed to the proper mil thickness (to achieve 50 percent aggregate embedment), and that the 

aggregate is applied as soon as possible after resin binder application. With manual application 

methods, each of these processes offers potential for human error and a poor installation. Fully 

automated application seeks to eliminate much of the opportunity for human error, although 

there is still potential for human error in the setup and operation of fully-automated vehicles. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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Table 12. Key advantages and disadvantages of application methods. 

Fully-Automated Manual

Advantages Advantages

• Automated conditioning, metering, blending, and 

application of resin binder

• Real-time adjustment of resin binder component 

ratio and application rate

• Uniform mil thickness of resin binder to eliminate 

high points and uneven wear on the finished surface

• Immediate and automated application of aggregate 

onto the resin binder layer

• Automated metering and real-time adjustment of 

aggregate placement

• Smaller installation crew and faster application 

(reduced exposure of workers and quick re-opening 

to traffic) 

• Automated recording of material usage and options 

for real-time reporting during installation

• Minimal initial cost for tools and equipment

• Flexibility of placement (to accommodate 

varying withs and irregular areas)

• Few opportunities for equipment 

breakdown (if using mechanically-assisted 

methods) and manual methods can be used 

as a backup 

Disadvantages Disadvantages

• May be difficult to navigate tight curves and confined 

installations

• Generally fixed installation width

• High initial cost and maintenance cost of equipment

• High mobilization cost

• No backup if equipment breaks down

• Potential variability in binder proportioning 

and blending (using manual methods)

• Variability in resin binder thickness

• Slower installation

• Larger installation crew required

• Delayed placement of aggregate after resin 

binder

5.4 SPECIAL CIRCUMSTANCES AND CONSIDERATIONS 

Open Graded Friction Course (OGFC)—Many States regularly use OGFC or permeable 

friction course surfaces due to the surface drainage and friction benefits they provide in areas 

with high amounts of rainfall. However, placement of HFST over open graded surfaces is not 

recommended for the following reasons: 

• Resin binder demand—Resin binder will drain down into porous pavement surfaces, 

requiring significantly more resin binder to achieve the 50-65 mil thickness for the 

surface aggregate. If placement over an open graded surface cannot be avoided, a double 

layer HFST may be considered, but may lead to thermal compatibility issues. 

• Issues with thermal compatibility—As resin binder fills the pores of an open 

graded surface, it effectively creates a very thick layer (i.e., equal to the thickness of the 

open graded layer) of HFST resin binder, which will have different thermal properties 

than the underlying asphalt pavement. This can lead to delamination of the open-graded 

layer and HFST from the underlying asphalt or cohesive failure within the underlying

asphalt pavement during thermal cycling. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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• Poor performance of past applications—After poor performance of several 

projects, FDOT no longer permits HFST to be installed over OGFC. FDOT requires 

that any OGFC be removed (using milling) and replaced with dense-graded asphalt mix 

prior to HFST installation within the HFST treatment limits.

Double Layer HFST—A double layer HFST has been used by some agencies for very high 

traffic volume locations where there is a higher likelihood a single layer application will wear off 

faster (e.g., urban mainline locations on interstates or State highways). However, a double layer 

HFST comes with certain risks which should be carefully weighed, including: 

• A two-layer HFST is much less flexible than a single layer system due to the thickness of 

the resin binder. This can increase shear forces at the bond interface due to differing 

thermal properties from the underlying pavement, potentially leading to delamination or 

substrate failure. 

• A two-layer HFST is less permeable than a single layer system, which increases vapor 

pressure between the HFST and underlying pavement. This can increase the potential 

for stripping of underlying bituminous pavement surfaces and eventual failure. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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CHAPTER 6—HFST INSPECTION GUIDE 

This chapter provides a guide for HFST installation inspection using either the manual or fullautomated methods discussed in chapter 5. Key elements of each aspect of a typical HFST 

installation will be discussed, although this information will vary based on agency-specific 

requirements. An inspection checklist is provided in Appendix C, and a pocket guide is available 

for download from FHWA for use on mobile devices (FHWA, forthcoming). 

6.1 OVERVIEW OF HFST

HFST is a pavement surface treatment used specifically to dramatically increase the skid 

resistance of virtually any pavement surface for the purpose of reducing friction-related crashes. 

HFST is installed by spreading a thin layer of polymeric resin binder (typically epoxy or 

polyester) over the pavement surface, then broadcasting or dropping a 1-3 mm nominal-size 

polish and abrasion-resistant aggregate onto the resin layer. The finished surface is a thin, 

superficial, pavement surface treatment that can be applied during a short closure of the 

roadway. Figure 18 shows an HFST placed over a conventional asphalt pavement surface.

© The Transtec Group

Figure 18. Photograph. HFST placed over a conventional asphalt pavement surface 

(Merritt et al. 2020a). 
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6.2 PRE-CONSTRUCTION 

Key considerations for HFST inspection to verify prior to construction include:

1) Review of contractor/installer QCP to verify:

• Schedule for the test strip and full-scale/production of HFST placement (if test 

strip is to be completed separately).

• Description of equipment for placing HFST.

• Methods for conditioning, metering, blending, and applying resin binder.

• Methods for applying aggregate, including timing of placement onto resin binder.

• Methods for monitoring and documenting material usage. 

• Method for protecting areas that will not receive HFST.

• Description of acceptable environmental conditions (temperature and 

precipitation) for placing HFST.

• Cure time and time to opening to traffic estimates for HFST.

• Storage and handling of HFST materials.

• Disposal and recycling of excess HFST and containers.

• Contingency plan for possible failure during the HFST application.

• Name of the certified independent testing laboratory.

• Key personnel and contact information.

• All project certifications and test results. 

2) Verify name and contact information for contractor QCP administrator. 

3) Check that materials supplied to the project meet specification requirements (through 

agency testing or from certified test results from the installer).

4) Verify that a resin binder manufacturer’s representative is present for initial/test strip

installation.

6.3 HFST MATERIALS INSPECTION 

HFST consists of two materials, polymeric resin binder and calcined bauxite aggregate. The 

following are key considerations for inspecting these materials. 

6.3.1 RESIN BINDER

• Verify that resin binder type and brand supplied to the project site is what was specified 

in the QCP and approved for use. 

• Verify that resin binder conforms to agency specifications if certified test results were 

provided by the installer in lieu of agency testing. 

• Verify proper storage of materials for ambient conditions: 

o Resin binder components should be stored in sealed, watertight containers.

o Resin binder should be stored as recommended by manufacturer 

(heated/cooled/shaded locations as required). 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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• Verify resin binder component containers are clearly labeled with: resin component 

(e.g., Part A, Part B, etc.), brand name, name of manufacturer, lot or batch number, 

temperature range for storage, expiration date, and quantity of material in container. 

• Sample materials for verification testing on-site as required by specification.

• Verify that adequate quantities of resin binder components for the intended installation 

are on-site or accessible near the project site.

6.3.2 CALCINED BAUXITE AGGREGATE

• Verify that aggregate packaging is clearly labeled with: type of aggregate, manufacturer, 

and location of processing.

• Verify that aggregate conforms to agency specifications if certified test results were 

provided by the installer in lieu of agency testing. 

• Verify that aggregate is packaged and stored in such a way to protect it from rain.

• Verify that adequate quantity of aggregate for the intended installation is on-site or 

accessible near the project site. 

• Sample materials for verification testing on-site as required by specification.

• Assess aggregate cleanliness: 

o Examine aggregate material in packaging or installation vehicle for presence of 

foreign matter. 

o Observe loading of aggregate into installation vehicle to check for segregation 

and assess cleanliness (dust generation). 

• Verify aggregate is dry and there is no visible moisture on the stockpile or within the 

stockpile when sampled by hand. Sample and test for moisture if questionable. 

• If reclaimed aggregate is permitted, verify that reclaimed material has been remixed with 

virgin material at the specified minimum ratio (typically 2:1 or 3:1 virgin to reclaimed).

6.4 SURFACE PREPARATION INSPECTION 

The various aspects of surface preparation prior to HFST application are discussed below. 

6.4.1 TREATMENT OF PAVEMENT DISTRESSES 

The types of underlying pavement distresses to be addressed prior to HFST application should 

be clearly outlined in the project plans and specifications. Note that some distresses will 

require patching or the complete removal and replacement of pavement surfaces, which 

typically require 30 days of cure time before HFST can be applied. Most agency specifications 

require pre-treatment of non-working cracks wider than 0.25 inches with HFST resin binder, 

which can be completed just prior to HFST application. 

• Verify that all distresses identified for treatment in the project plans have been 

addressed or will be addressed during installation. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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• Note that crack sealing using bituminous crack sealant should be flush with or slightly 

recessed from the top surface of the pavement (figure 19) and not overbanded onto the 

pavement surface. 

• Bituminous crack sealant should be allowed to cure for at least 30 days prior to HFST 

application.

© The Transtec Group 

Figure 19. Photo. Example of bituminous crack sealant in asphalt pavement 

recessed from the top surface of the pavement.

6.4.2 CLEANING AND ROUGHENING OF THE PAVEMENT SURFACE

• Verify that compressed air wash is completed in accordance with specifications 

(AASHTO Specification: minimum 180 CFM with tip of lance within 12 inches of 

surface) and that the surface is fully covered by the air wash (figure 20). 

• For concrete pavement, verify that the specified CSP (AASHTO Specification: minimum 

5) has been achieved with the shotblasting process (figure 21, figure 22). Verify that 

entire surface to receive HFST has been shotblasted. Ensure that a compressed air wash 

has been used to remove latent dust and verify that the prepared surface is free from 

dust. 

• If a power broom or vacuum truck are used to clean the surface, ensure that these are 

not generating additional dust and are followed by a compressed air wash to remove 

latent dust. 

• For a double layer HFST, verify that all loose aggregate has been removed from the first 

layer before application of second layer. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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© The Transtec Group 

Figure 20. Photo. Example of compressed air wash surface preparation.

© The Transtec Group 

Figure 21. Photo. Shotblast surface preparation showing overlap between 

successive passes. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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© KwikBond Polymers 

Figure 22. Photo. Shotblast concrete surface with CSP = 5.

6.4.3 STRIPING AND PAVEMENT MARKING REMOVAL AND MASKING

• Verify complete removal of any pavement striping or markings as required in the project 

plans and specifications. 

• Check the integrity of the pavement surface where the striping/markings were removed 

to verify that there is no damage (e.g., raveling) from the removal process (figure 23).

• Verify that any pavement striping or markers to be left in place have been properly 

masked off as required in the project plans and specifications. 
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© The Transtec Group 

Figure 23. Photo. Example of pavement striping removal using milling which has 

not damaged the underlying pavement.

6.4.4 PROTECTION OF JOINTS AND DRAINAGE STRUCTURES

• Verify that any pavement joints (e.g., concrete pavement joints, bridge approach joints, 

etc.) have been masked off as required in project plans and specifications.

• Verify that any drainage structures (e.g., inlets, manholes, etc.) have been properly 

masked off as required in project plans and specifications (figure 24). 

© WSDOT 

Figure 24. Photo. Example of masking of drainage structures near HFST 

application.
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6.4.5 PROTECTION OF THE PREPARED SURFACE PRIOR TO APPLICATION 

• Verify that the surface is clean and dry prior to HFST application. If the surface has been 

opened to traffic after cleaning and roughening, verify that the surface has not been 

affected by traffic. 

• Check cracks, joints, and surface pores for dirt and moisture. 

• Check moisture content of surface if required in project specifications. ASTM D 4263, 

“Indicating Moisture in Concrete by the Plastic Sheet Method,” modified to a two-hour 

test can be used for this purpose. 

• Monitor prepared surface prior to and during installation for any contaminants from 

installation vehicles (oil, hydraulic fluid, air conditioner condensate, etc.). 

6.5 HFST APPLICATION INSPECTION 

This section will address application methods and provide inspection guidance on key aspects of 

various application practices for both manual application and fully-automated methods. General 

principles for HFST application inspection, regardless of the method include:

• Ensure resin binder is properly proportioned to manufacturer specifications for 

installation conditions (pavement and air temperature) and thoroughly blended such that 

it fully cures after application. 

• Ensure resin binder is applied to the required mil thickness, verified using a wet film 

thickness gage (if appropriate, figure 25) and through a comparison of anticipated to 

actual coverage rate. 

• Ensure aggregate is applied to the resin binder before it gels and that all resin binder is 

covered. 

• Prevent vehicular traffic on the HFST surface before it has cured. 
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© The Transtec Group 

Figure 25. Photo. Wet film thickness gage used to measure resin binder thickness 

during application. 

6.5.1 MANUAL APPLICATION 

Resin Binder Proportioning and Blending

The following is a general list of tools and equipment for manual resin binder proportioning and 

blending (figure 26). 

• Tarps/plastic sheeting to protect work area. 

• Nozzles for resin totes. 

• Clean measuring containers (resin type dependent). 

• Variable speed drill (primary and backup). 

• Generator for mixing drill. 

• “Jiffy” style mixer for blending. 

• Timer for resin blending. 

• Clean mixing container (with wheels if using for transport). 

• Rags for clean-up and cleaning spills. 

• For mechanically assisted resin binder proportioning and blending. 

For inspection of manual resin binder proportioning and blending:

• For manual proportioning and blending, verify that resin binder components are 

proportioned to the correct ratio. 

• For mechanically-assisted proportioning and blending, verify the metering process used 

to proportion the resin binder components to the proper ratio. 

• Routinely sample the blended material to ensure that it cures/hardens. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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© The Transtec Group 

Figure 26. Photo. Typical tools and equipment for resin binder proportioning and 

mixing for manual application.

Resin Binder Application 

The following is a general list of tools and equipment for manual resin binder application: 

• Duct tape/tar paper to form start/end joint. 

• Wheelbarrow or wheeled mixing container for transporting resin from blending to 

placement location (may not be necessary for mechanically-assisted reason binder 

proportioning and blending). 

• Spiked shoes for squeegee operator to prevent shoeprints in resin binder (figure 27). 

• Notched rubber squeegee for spreading resin binder with provision of additional 

squeegees for replacement when notches/serrations become worn (figure 28). 

• Wet film thickness gauge (figure 25). 
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Source: FHWA 

Figure 27. Photo. Example of spiked shoes worn by squeegee operator.

Source: FHWA 

Figure 28. Photo. Notched rubber squeegee for spreading resin binder during 

manual application.

The following is a general list of checks for inspection of manual resin binder application (figure 

29): 

• Note ambient and pavement surface temperatures regularly during application. 

• Verify use of tar paper (or similar) masking to create clean construction joints at the 

beginning and end of the placement.

• Note resin binder viscosity and if it appears too thick or too thin.

o If resin binder is too thick, it may be difficult to spready uniformly.

o If resin binder is too thin, watch for resin binder sheeting across the lane or 

down the pavement grade leaving deficient thickness at the high side. 

• Watch for resin binder running off the lane, potentially leaving inadequate thickness. 

• Verify complete coverage of the treated area with resin binder before aggregate 

application. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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• Note the method used to operate the squeegee. Squeegees should be pulled towards 

the operator rather than pushed. 

• Note any changes in color or consistency of resin binder throughout application and 

watch for contaminants (e.g., deleterious materials or residual hardened resin binder) as 

resin binder is deposited onto the pavement surface. 

• Verify resin binder mil thickness with a wet film thickness gage at the frequency 

prescribed in the specifications.

• Verify total material quantity usage at the end of placement for comparison with 

expected usage based on required mil thickness.

© KwikBond Polymers 

Figure 29. Photo. Example of manual resin binder application. 

Aggregate Application 

The following is a general list of tools and equipment for manual aggregate application. 

• Wheelbarrows (2-wheeled preferred). 

• Shovels (flat head preferred). 

• 5-gallon buckets. 

• For mechanically-assisted aggregate application, only 5-gallon buckets may be necessary. 

The following is a general list of checks for inspection of manual aggregate application (figure 

30): 

• Verify that aggregate is applied using a method that does not disturb (shove) the resin 

binder, ideally from the shoulder or adjacent lane. 

• Watch for foreign material and significant dust content in aggregate as it is applied.

• Verify that aggregate is applied to the wet resin binder before gelling occurs and within 

the prescribed timing from project specifications or manufacturer recommendations. 

• Verify that all resin binder is completely covered such that no “wet” areas of resin 

binder show through the aggregate before resin gels.
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• Verify that aggregate application remains behind resin binder application such there is no 

aggregate on the pavement surface before the resin binder. 

• Verify uniform thickness of aggregate application. 

• Verify total material quantity usage at the end of placement for comparison with 

expected usage from project specifications. 

© The Transtec Group 

Figure 30. Photo. Example of manual application of HFST aggregate.

6.5.2 FULLY-AUTOMATED APPLICATION 

Resin Binder Application 

• Verify functionality of resin binder component metering system and proportioning to 

the required blending ratio. 

• Routinely sample blended material to ensure that it cures/hardens.

• Note ambient and pavement surface temperatures regularly during application. 

• Verify use of tar paper (or similar) masking to create clean construction joints at the 

beginning and end of the placement.

• Observe resin binder application, noting any issues with consistency of the material or 

uniformity of coverage (figure 31). 

• Note any excessive use of rollers and squeegees to correct automated application 

issues. 

• Verify resin binder mil thickness with a wet film thickness gage, if possible, at the 

frequency prescribed in the specifications.

• Verify total material quantity usage at the end of placement for comparison with 

expected usage based on required mil thickness.
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Aggregate Application 

• Verify that aggregate application method does not interfere with resin binder application 

or disturb (shove) the resin binder. 

• Watch for foreign material and significant dust content in aggregate as it is deposited.

• Observe aggregate application, noting any issues with uniformity of coverage (figure 31). 

• Verify that all resin binder is completely covered such that no “wet” areas of resin 

binder show through the aggregate before resin gels, using manual aggregate application 

to cover these areas as needed. 

• Verify total material quantity usage at the end of placement for comparison with 

expected usage from project specifications.

© Florida DOT 

Figure 31. Photo. Example of fully automated resin binder application followed by 

automated aggregate application demonstrating uniformity of coverage. 

6.6 INSPECTION OF AGGREGATE REMOVAL 

The primary purpose of aggregate removal is to remove the loose excess aggregate from the 

HFST after the resin binder has cured. A secondary purpose is to loosen and remove lightlybonded aggregate to help minimize the amount of shedding over the first few days and weeks 

after opening to traffic. 

6.6.1 METHODS 

Removal of excess aggregate is generally always completed using some form of a power broom

(figure 32), vacuum sweeper (figure 33), or combination broom-vacuum. Power brooms tend 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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to be most effective and efficient, generally only requiring 1 to 2 passes, but may not be possible 

to use if there is risk of sweeping aggregate into adjacent lanes. Whenever broom methods are 

used, only non-metallic, less aggressive broom bristles should be permitted. If aggregate reuse is 

permitted, vacuum sweepers are generally the most efficient method for reclaiming aggregate. 

However, because vacuum sweepers do not agitate the surface like power brooms, 3 to 4 

passes may be necessary to remove all loose aggregate. Agencies may have requirements for 

dust mitigation that will require one method over another. 

© The Transtec Group 

Figure 32. Photo. Example of aggregate removal using a power broom.

© The Transtec Group 

Figure 33. Photo. Example of aggregate removal using a vacuum truck.
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6.6.2 TIMING 

Timing of aggregate removal is critical. If sweeping/vacuuming begins before the resin has 

adequately cured, there is risk of pulling aggregate out of the resin binder, potentially 

diminishing the frictional properties of the finished surface. Timing of aggregate removal will be 

dictated by resin binder manufacturer guidelines based the cure time requirements and ambient 

temperature at placement. Deformability of the resin binder is typically used to determine 

timing of sweeping in the field. Note that cure time required before sweeping may be different 

from that required before opening to traffic. 

6.6.3 RECLAMATION 

If reuse of aggregate is permitted, reclaimed aggregate should be stored separately from virgin 

aggregate such that they can be remixed in the proper proportions for future application. 

6.6.4 INSPECTION 

• Verify that the sweeping time is in accordance with the resin binder manufacturer 

recommendations, and resin cure has been verified before sweeping begins. 

• Note any areas where sweeping exposes the resin binder or underlying pavement

(figure 34). These areas will require repair or replacement. 

• Verify that all loose aggregate has been removed from the surface of the HFST before 

opening to traffic.

• Verify that all aggregate which has migrated onto adjacent lanes, paved shoulders, or 

pavement adjacent to the beginning or end of the HFST section has been removed

(figure 35). 

• Verify that reclaimed aggregate is stored separately from virgin aggregate. 

© The Transtec Group 

Figure 34. Photo. Example of exposure of underlying pavement after sweeping.
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© The Transtec Group 

Figure 35. Photo. Example of loose aggregate migration onto adjacent lanes and 

shoulders.

6.7 INSPECTION OF FINISHED SURFACE

Before opening to traffic, the finished surface should receive a final visual inspection. Visual 

inspection should include:

• Verify that there is no loose aggregate on the HFST surface or adjacent surfaces.

• Verify that there are no areas of discoloration that could indicate uncured resin or 

moisture beneath the treatment (figure 36). 

• Verify that all masking of striping, pavement markers, joints, drainage structures, etc. 

has been removed. 

• Identify any areas where HFST is missing (figure 37) or will need to be removed and 

replaced for non-conformance. 

o Verify that the surface is safe to open to traffic before these repairs are made. 

o If surface is not safe to open to traffic, discuss mitigation and repair/replacement 

plan with installer. 

• Verify that all striping has been replaced with temporary or permanent markings in 

accordance with project plans and specifications. 
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© The Transtec Group 

Figure 36. Photo. Example of discoloration indicating uncured resin binder.

© The Transtec Group 

Figure 37. Photo. Example of areas where HFST is missing and will require repair.

6.8 ACCEPTANCE TESTING 

Acceptance testing is specific to agency requirements. In addition to the visual inspection of the 

finished surface discussed above, acceptance testing typically includes friction testing, but may 

include macrotexture testing and pull-off testing.
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6.8.1 FRICTION TESTING 

Friction testing may be required before opening to traffic but is most commonly required 14 to 

90 days after opening to traffic to allow a wear-in period. Agencies with performance guarantee 

requirements may also require testing during or at the end of the performance period. 

The most common methods for friction testing are, ASTM E274/AASHTO T 242 LWST (ASTM 

2020b, AASHTO 2018b), which can be performed under traffic, and ASTM E 1911 DFT (ASTM 

2019a), which will require a lane closure.

• Verify the test requirements in the project specifications, including timing, number of 

tests required, test speed, friction value for acceptance. 

• Verify that the test is performed in accordance with project specifications and any 

ASTM/AASHTO/agency-specific procedures. 

6.8.2 MACROTEXTURE TESTING 

Macrotexture testing is typically completed at the same time as friction testing. The two most 

common methods for macrotexture testing are stationary methods that will require a lane 

closure. The ASTM E 965 “Sand Patch” method uses a known volume of sand or glass beads to 

estimate macrotexture depth, reported as MTD (ASTM 2019b). The ASTM E2157 Circular 

Track Meter measures macrotexture over a circular path and reports it as MPD. 

• Verify the test requirements in the project specifications, including timing, number of 

tests required, and friction value for acceptance. 

• Verify that the test is performed in accordance with project specifications and any 

ASTM/AASHTO/agency-specific procedures. 

6.8.3 OTHER TESTS 

Some agencies may have additional acceptance testing requirements, such as the ASTM C1583 

pull-off tensile strength test to verify adhesion between the HFST and underlying pavement

(ASTM 2020c). This is also a stationary test which will require a lane closure but can typically 

be performed after installation, before opening to traffic. 

6.9 EARLY-AGE MONITORING 

Early-age monitoring will help identify any issues related to materials and installation 

workmanship. These issues will typically develop within the first 30 to 60 days after installation. 

Summarized below are potential early-age items to monitor.

6.9.1 UNCURED RESIN BINDER

Uncured resin binder will normally appear as isolated areas where the HFST is discolored 

(figure 36) and soft, and will lead to aggregate loss or flushing of the resin binder on the HFST 

surface. This may not appear immediately and may develop over the first few days after 
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84 

installation. Agencies may investigate discoloration and determine the limits of the resin binder 

failure as it may not affect the entire application. 

Agencies may remove and reapply the HFST in the affected area(s) to correct the resin binder 

failure. 

6.9.2 AGGREGATE LOSS AND RE-SWEEPING 

HFST will naturally shed aggregate that is only lightly bonded to the resin binder under traffic 

wear. Normal shedding will generally be heaviest during the first 24 to 72 hours, tapering off 

over time, depending on traffic volume. Shed aggregate will generally accumulate along the 

edges of the lane and possibly in adjacent lanes and paved shoulders (figure 38). Re-sweeping is 

typically required in project specifications to remove this loose material within the first 2 to 4 

weeks of installation. 

If significant aggregate loss continues beyond the first 30 to 60 days, this may indicate an issue 

with materials and installation and the cause should be investigated further, particularly if the 

resin binder or underlying pavement becomes exposed. 

Corrective action for aggregate loss is removal and reapplication of the affected area(s).

© The Transtec Group 

Figure 38. Photo. Example of aggregate shedding and accumulation along lane edge 

and on paved shoulder.

6.9.3 DELAMINATION 

Delamination is the separation of the HFST from the underlying pavement due to a lack of 

bond. Delamination generally manifests as “sheets” of HFST peeling away from the surface, 

commonly in small localized areas, but can spread to much larger areas (figure 39). 
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Delamination is not obvious until the HFST peels away, leaving exposed pavement, but may still 

be occurring. Sounding techniques can be used to identify delamination if there is evidence that 

this may be occurring. 

Corrective action for delamination is removal of all affected areas and reapplication of HFST. 

Widespread delamination may necessitate complete removal and reapplication, ensuring that 

any possible causes of the delamination (e.g., surface preparation) are addressed before 

reapplication.

© The Transtec Group 

Figure 39. Photo. Example of delamination of HFST from underlying pavement 

surface.

6.9.4 AGGREGATE POLISHING

Aggregate polishing is the result of aggregate particles being worn away under traffic, leaving a 

smooth HFST surface where the aggregate may be worn flush with the resin binder (figure 40). 

While this should not occur if calcined bauxite aggregate meeting specification requirements is 

used, if it does occur, the aggregate should be further investigated with laboratory testing. 

Corrective action for aggregate polishing will be removal and reapplication of the HFST. 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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© The Transtec Group 

Figure 40. Photo. Example of polished HFST surface in wheelpaths.

6.9.5 DISCOLORATION 

Discoloration is a visible difference in color of localized areas of HFST from the surrounding 

surface (figure 41). Discoloration does not necessarily indicate a problem with the HFST, but 

may be an indicator of the presence of moisture trapped beneath the HFST. Monitoring should 

continue over time to note any changes in discoloration or appearance of localized distresses. 

Corrective action would only be necessary if it leads to distresses. 

© The Transtec Group 

Figure 41. Photo. Example of HFST discoloration likely caused by moisture. 
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6.9.6 SURFACE WEAR LOSS OF HFST 

Surface wear loss of HFST occurs when both the aggregate and resin binder wear off under 

traffic. This generally occurs when the aggregate polishes or breaks away from the resin binder, 

exposing the resin binder which quickly wears off, exposing underlying pavement (figure 42). 

While wear-off is expected at the end of HFST service life, premature wear-off is a cause for 

concern and should be investigated further, as it may indicate that the resin binder layer was 

placed too thin. 

Corrective action for wear-off is reapplication of HFST either over the existing surface (if 

recommended by the resin binder manufacturer) or after removal of the worn layer. 

© The Transtec Group 

Figure 42. Photo. Example of HFST worn off in the wheelpaths.

6.9.7 FRICTION LOSS 

Friction loss is defined as a sustained decrease in friction over time. While there will naturally 

be some loss of friction over the first year after installation as the surface is worn in under 

traffic, continued loss of friction (e.g., 10 percent or more) year after year, should be

investigated further. Generally, this condition is caused by polishing or loss of aggregate. 

Corrective action for friction loss is reapplication of HFST either over the existing surface (if 

recommended by the resin binder manufacturer) or after removal of the existing surface. 

6.9.8 FAILURE OF UNDERLYING PAVEMENT 

Failure of the underlying pavement will cause a loss of HFST. Failures typically manifest as small 

isolated areas (e.g., potholes) which can progress to much larger areas (figure 43). This type of 

failure is more common in asphalt pavements and may be the result of a cohesive failure within 

a weak asphalt layer or due to stripping of the asphalt layer due to trapped moisture. 
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Corrective action for failure of the underlying pavement will require removal of the affected 

area, proper repair of the underlying pavement, and reapplication of HFST. 

© The Transtec Group 

Figure 43. Photo. Example of failure of underlying pavement leading to isolated 

failures (potholes) of HFST.

6.10 INSPECTION CHECKLIST 

Appendix C provides an example of an inspection checklist covering the various inspection 

items discussed above. This checklist provides a quick verification that each of these items are 

addressed during installation by the inspector. An editable Microsoft Word version of this 

checklist along with a stand-alone inspection guide is available for download from FHWA. 
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CHAPTER 7—PERFORMANCE MONITORING AND 

REPLACEMENT 

Monitoring the performance of HFST installations is important for the further refinement of 

specifications and site selection processes for future implementation. This chapter will discuss 

common causes of HFST failure followed by consideration for performance monitoring and 

additional considerations for the removal and replacement of HFST. 

7.1 CAUSES OF HFST FAILURE 

When discussing HFST failure, a distinction is made between premature failure and terminal 

failure. Premature failure is typically related to the site conditions (e.g., underlying pavement 

integrity), materials, or installation practices. Terminal failure is typically characterized by a loss 

of pavement friction due to aggregate loss under traffic wear over time. While there are likely a 

number of other failure mechanisms, summarized below are some of the most common. 

Proper site screening (chapter 3), materials (chapter 4), specifications (chapter 5), and 

installation practices (chapter 6) will help prevent premature failure of HFST.

• Resin binder formulation and blending—Improperly formulated resin binders or 

resin binders which are not properly blended before application can result in a resin 

binder that will not have the desired properties necessary to bond to the pavement 

surface or securely hold the aggregate in place. Virtually all resin binders are two (or 

more) part materials that must be blended in the proper proportions to ensure proper 

curing. Soft or uncured areas of resin binder after application are an indication of 

improper formulation or improper blending (figure 44 and figure 45).

© FDOT

Figure 44. Photograph. Example of localized failures due to poor binder mixing

(FDOT 2021). 
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© FDOT

Figure 45. Photograph. Example of soft areas in resin binder shortly after 

construction (FDOT 2021). 

• Inadequate resin binder thickness—The target embedment depth for HFST 

aggregate in the resin binder is 50 percent of the nominal aggregate size. If the resin 

binder layer is too thin, aggregate particles will be more easily be dislodged from the 

resin binder during sweeping (figure 34 and figure 46) or under traffic wear, leaving only 

the resin binder which provides no frictional benefit. Inadequate thickness typically 

results from an inadequate coverage rate for the pavement macrotexture. Specifications 

for resin binder coverage rate should account for pavement macrotexture, ensuring 

adequate resin binder material for the level of macrotexture in the pavement surface to 

be treated. Low viscosity of the resin binder is another cause of inadequate thickness. If

the material lacks viscosity, it will flow or run down the pavement slope, leaving 

inadequate thickness at the higher points. 

© The Transtec Group

Figure 46. Photograph. Example exposure of underlying pavement due to 

inadequate resin binder thickness. 
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• Improper aggregate application—If the aggregate is not broadcast onto the resin 

binder before it begins to gel, the resin binder will resist penetration and bond of the 

aggregate and the aggregate will more easily be dislodged during sweeping or under 

traffic wear, leaving only the resin binder. Figure 47 shows a photo of resin binder with 

only minimal aggregate embedded as a result of delayed application of the aggregate. 

While the timing of aggregate application will vary with resin binder and temperature, 

best practice is to apply the aggregate immediately after the resin binder application. 

Dirty aggregate can be another source of premature aggregate loss as the aggregate 

does not properly bond to the resin binder and can become dislodged under traffic 

wear. 

© Transtec Group 

Figure 47. Photograph. HFST with inadequate aggregate coverage due to delayed 

aggregate application. 

• Delamination due to lack of macrotexture on existing pavement or 

improper surface preparation—Resin binder bond to the pavement surface is partly 

mechanical, meaning the resin binder interlocks with the pavement surface through 

macrotexture. If a pavement surface lacks adequate macrotexture, this mechanical bond 

is diminished. A poor bond can also be the result of improper surface preparation when 

the surface is not thoroughly cleaned, leaving latent dust that inhibits the bond between 

the resin binder and pavement surface. The result of either condition is typically a 

delamination of the HFST from the pavement surface, as shown in figure 39 and figure 

48. This issue is more common with smooth concrete surfaces that have not been 

shotblasted or with bituminous surfaces exhibiting bleeding or flushing. Shotblast surface 

preparation helps to ensure adequate macrotexture, and thorough air wash helps to 

remove latent dust.
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© Transtec Group 

Figure 48. Photo. Example of an area of HFST delamination from the underlying 

pavement surface.

• Failure of underlying pavement—If the underlying pavement is in poor condition, 

or if moisture becomes trapped in the underlying pavement (e.g., from subsurface 

moisture migration or surface intrusion at cracks leading to asphalt stripping), the 

pavement can fail and cause failure of the HFST as well. Underlying pavement failures 

typically manifest as isolated distresses (potholes) in the HFST as shown in figure 43 and 

figure 49. While these may remain isolated failures, they can spread to much larger 

areas. 

Source: FHWA

Figure 49. Photograph. Example failure of underlying pavement (delamination of 

surface layer) resulting in failure of HFST. 

Failure of the underlying pavement can also be the result of high shear stresses in the 

underlying pavement, resulting in a cohesive failure (figure 50). The HFST remains 
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bonded to the underlying pavement, but failure occurs within the pavement itself. This 

type of failure is typically caused by a weak asphalt layer and may be exacerbated by 

thermal incompatibility between the HFST and underlying pavement which increases 

these shear stresses under thermal cycling, as well as by vehicle-induced shear stresses 

(FDOT 2021, Waters 2011). 

© Waters

Figure 50. Graphic. Cohesive failure of underlying pavement (Waters 2011). 

7.2 PERFORMANCE MONITORING 

As with the implementation of any safety countermeasure, performance monitoring includes 

regular evaluations of safety performance (e.g., crash reduction). For HFST, however, 

performance monitoring also includes regular evaluation of functional performance (e.g., friction 

and treatment deterioration). Section 7.2.1 provides considerations and methods for 

monitoring HFST safety performance and Section 7.2.2 provides considerations and methods 

for monitoring HFST functional performance. 

7.2.1 SAFETY PERFORMANCE 

Monitoring safety performance of HFST installations will allow an agency to optimize 

deployment of this safety countermeasure through refinement of site selection processes and 

an improved understanding of the B/C for HFST. In general, there are three levels of safety 

performance evaluation: project, countermeasure, and program (Gross 2017). 

• Project-level evaluation—The purpose is to evaluate individual projects over time to 

assess changes in crash frequency and severity against the before condition.

• Countermeasure-level evaluation—The purpose is to evaluate groups of similar 

projects to determine the effectiveness in changes to crash frequency and severity with 

the intention of developing a CMF. This includes identifying factors associated with 

HFST being more or less effective to inform future decision-making. 

• Program-level evaluation—The purpose is to evaluate the overall HFST program to 

measure the effectiveness with respect to changes in crash frequency and severity by 

crash type at the system level. This evaluation level helps to demonstrate the value of 
HIGH FRICTION SURFACE TREATMENT SITE SELECTION AND INSTALLATION GUIDE

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the HFST program. Agencies can also use program evaluations to identify opportunities 

to improve processes and procedures. 

There are several techniques available for conducting evaluations at each level. The HSIP 

Evaluation Guide provides details specific to each with a separate chapter devoted to each 

evaluation level (Gross 2017). However, the analytical methods are relatively similar for each 

level and should be determined based on data availability, sample size, and the desired level of 

confidence in the results. Table 13 provides an overview of potential analytical methods and 

when each may be most appropriately applied.

Table 13. Safety Performance Evaluation Methods

Evaluation 

Method Advantage

Potential Biases/ 

Implementation 

Issues

Data Needs Most appropriate for

Simple 

before-after

Straightforward 

application

Regression-to-mean

Traffic volume changes

Time trends

Crashes before and 

after

Project evaluation

Not looking for generalized 

effectiveness

Volume data unavailable

Before-after 

with traffic 

volume 

correction

Straightforward 

application

Accounts for 

traffic volume

Regression-to-mean

Assumes linear crash 

rate

Time trends

Volume and crashes 

before and after

Project evaluation

Not looking for generalized 

effectiveness

Before-after 

with 

comparison 

group

Accounts for 

several biases

Does not 

require SPFs

Regression-to-mean

Assumes a linear crash 

rate

Appropriate 

comparison sites

Volume and crashes 

before and after

Countermeasure evaluation 

Limited sample of sites

SPFs unavailable

Empirical 

Bayes 

before-after 

study

Accounts for 

most biases

Requires reference 

group for SPF 

development or 

calibration

Reference sites or 

calibrated SPF

Volume and crashes 

before and after

Countermeasure or program 

evaluation

Crosssectional 

study

Installation date 

not needed

Study can be 

conducted 

immediately

Potential confounding 

across sites

Does not compare 

before to after

Volume and crashes 

before and after

Confounding factors 

to reduce omitted 

variable bias

Countermeasure or program 

evaluation when installation 

dates unknown

Shift of 

proportions

Useful when 

traffic volume 

changes 

suspected but 

unavailable

Provides proportion, 

not change in 

frequency

Crashes before and 

after by type or 

severity

Evaluating changes to target 

crash type or severity

Volume data unavailable
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A key factor in all evaluation methods is that HFST project installations must be tracked for 

location, and for nearly all methods, the date of installation is required. Additionally, analysts 

should further consider the site selection method prior to evaluating safety performance. 

In general, the methods for evaluating HFST installed based on a site-specific approach and a 

systemic approach are the same. The data needs are the same, including the need for project 

details (installation locations and dates), traffic volume data, and crash data before and after 

installation. There is also a chance of regression-to-the-mean (RTM) bias when evaluating both 

site-specific and systemic applications, but potentially in opposite directions. RTM (or return to 

average) is the natural variation in crashes over time where sites with an abnormally high 

number of crashes in the past will likely experience a reduction in crashes in the future and vice 

versa even with no other changes to the site. The following are related challenges in evaluating 

site-specific and systemic HFST applications:

• Site-specific—When evaluating HFST at sites selected based on crash history, there is 

the potential for RTM to inflate the estimated effectiveness (i.e., crashes would have 

gone down even without treatment). While more reliable methods can help to account 

for RTM when evaluating the performance of individual projects, this is typically not 

done for a number of reasons. First, the focus of project evaluations is on whether or 

not the observed crash problem still exists at a specific location. Second, the results of 

individual projects may not be representative of all sites and agencies tend not to use 

the results of individual projects to make future decisions. Instead, agencies combine the 

results from multiple projects to estimate the general effectiveness of a 

countermeasure. When evaluating HFST to estimate countermeasure effectiveness and 

develop CMFs, analysts should use more reliable methods (e.g., EB before-after) to 

account for RTM and separate the natural variation in crashes from the effectiveness of 

HFST. 

• Systemic—When evaluating systemic HFST applications, there are challenges in 

accounting for sites that were treated but did not have any crashes in the recent past. If 

these sites experience even a single crash in the post-implementation study period, then 

a simple before-after method would indicate the HFST was ineffective. More reliable

methods (e.g., EB before-after) that incorporate predicted crash frequency provide a

better indicator of the change in safety performance. Additionally, a shift in proportions 

or other analytical method may provide further insight. The HSIP Evaluation Guide and 

NCHRP Report 955 provide further details and options for evaluating the safety 

performance of a systemic approach (Gross 2017; Torbic et al. 2020). 

To support performance monitoring and future decision-making, agencies can consider

developing robust agency-specific CMFs and B/C ratios. This can help to justify the general 

deployment of HFST and to better target the use of HFST to address friction-related safety 

issues. While there are several CMFs for HFST in the CMF Clearinghouse, these were 

generated from a limited number of jurisdictions (FHWA 2021a) that do not necessarily 

account for all of the possible conditions (e.g., climate, geography, traffic characteristics, etc.) in 
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the United States. Agency-specific CMFs will further improve the reliability of the crash 

reduction potential of HFST for jurisdiction-specific conditions. Gross et al. (2010) and Carter

et al. (2012) provide insights on developing high-quality CMFs as well as a discussion of 

considerations for improving the completeness and consistency in CMF reporting. 

7.2.2 FUNCTIONAL PERFORMANCE 

The two primary indicators of functional performance of HFST are friction performance and 

treatment condition.

Friction Performance

As a treatment used specifically to enhance pavement friction, monitoring HFST friction 

performance, or changes in friction over time, is critical. Routine friction testing (e.g., on an 

annual basis), preferably as part of a comprehensive PFMP, is recommended for proactively

monitoring HFST friction performance, as opposed to waiting for issues (e.g., increased crashes) 

to manifest before checking friction. 

If tested under a routine PFMP regime, HFST sections should be specifically identified in the 

PFMP database such that an appropriate investigatory/intervention level of friction specific to 

HFST is assigned to those segments. 

A sudden or rapid decrease in the friction of HFST is typically caused by aggregate polishing or 

aggregate loss. Assuming the proper aggregate materials were specified and verified during

installation, the latter condition is more common. Aggregate loss can be caused by a number of 

issues related to the resin binder, discussed above. 

Pavement friction testing methods should remain consistent such that results can be readily 

compared year-to-year (assuming annual testing). Alternatively, different friction thresholds can 

be established based on the potential devices used to measure friction. Furthermore, the use of 

CPFM is desirable as it can help identify variations in friction within the length of the treatment 

itself since friction may be lower at points of the highest friction demand. CPFM devices are 

also generally able to operate at locations (sharp curves and intersections) where other devices 

cannot. 

Initial friction requirements (test type and friction threshold) are defined by each agency. While 

the initial version of the AASHTO HFST specification (PP 79-14) called for FN40R = 65 for 

acceptance (which is very conservative for HFST) the current version leaves this to individual 

agencies. Chapter 5 provides examples of friction requirements for acceptance. 

While there is no codified standard for what would be considered an intervention friction value 

for HFST, several studies have examined both field and laboratory performance of HFST under 

normal traffic wear and accelerated wear to help determine what long-term friction values 

should be expected, as summarized in table 14. These studies reveal that HFST should maintain 

a friction value (FN40R) of at least 57-66 over time. The TCMS tool for evaluating margin of 

safety based on friction supply and friction demand uses a friction prediction curve which 
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assumes an initial friction value and a fairly rapid decay to a terminal value within a year where 

it remains over the life of the treatment (Pratt et al. 2018a, Pratt et al. 2018b). 

Table 14. Long-term friction performance of HFST. 

Source Friction Values

TCMS Tool Development, Pratt 2018b) 

• Field data from Florida and Texas HFST sites.

• Laboratory testing of samples subjected to 

accelerated wear with the three-wheel polishing 

test.

• Modelling based on Aggregate Imaging System of 

aggregates subjected so accelerated wear using 

Micro-Deval. 

Field Testing:

Initial: FN40R = 83 (based on SN50S = 70)

Terminal: FN40R = 57 (based on SN50S = 

50)

Modelled:

Initial: FN40R = 86 (based on SN50S = 73)

Terminal: FN40R = 67 (based on SN50S = 

58)

TCMS Model:

Initial: FN40R = 76 (based on SN50S = 65)

Terminal: FN40R = 66 (based on SN50S = 

57)

Field data from Florida HFST sites, (Wilson and 

Mukhopadhyay 2016)

Initial FN40R = 80

Long-Term (≤ 6 years) FN40R = 63

Field data from FHWA study to develop crash 

modification factors for HFST, (Merritt et al. 2020a). 

Long-Term (6 to 10 years) FN40R = 57-73 

(based on HFT(40) = 0.8-1.0)

NCAT Test Track, (Heitzman et al. 2015) Long-Term (>10M ESAL applications): FN40R 

= 63

Treatment Condition 

HFST condition should be routinely monitored as part of regular network-level pavement 

management condition surveys for distress and deterioration. If treatments are installed on 

rural roadways which do not receive regular (e.g., annual) condition assessment, agencies may 

need to perform project-level assessments. HFST sections should be clearly delineated in 

pavement management system databases such that they are not assessed with the same criteria 

as conventional pavement surfaces. It is important to note that the presence of distresses in 

HFST does not indicate a failed treatment. As long as the surface is still providing the desired 

level of friction, distresses should not be the primary indicator of a functional failure of an HFST 

unless the distresses are extensive and leading to potential safety hazards or maintenance 

liabilities. As such, project level condition surveys or field reviews of HFST sections should be 

performed if routine performance monitoring indicates a high level of distress. 

Common distresses and their potential impact on HFST performance are summarized below:

• Cracking—Any cracking or joints in underlying pavement (even if sealed prior to HFST 

application) will eventually reflect through into the HFST surface (figure 51). However, 
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experience has shown that this does not necessarily affect performance of HFST unless 

the underlying pavement begins to fail. In general, cracks in HFST should not be sealed 

as part of routine maintenance as the sealant can affect the skid resistance of the 

surface. 

© The Transtec Group

Figure 51. Photograph. Example of cracking in underlying pavement reflecting 

through HFST. 

• Aggregate Loss—Also sometimes referred to as raveling, HFST aggregate loss (figure 

42 and figure 52) will lead to a loss of friction and can be caused by a number of factors 

discussed previously. Unfortunately, there are no established methods quantifying 

aggregate loss aside from visual subjective inspection. While automated pavement 

condition assessment continues to improve, the only metric which appears to correlate

to some degree with aggregate loss is macrotexture, or MPD. 
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© The Transtec Group

Figure 52. Photograph. Example of aggregate loss under traffic wear.

• Aggregate Polishing—While it may be possible to visually identify aggregate polishing 

(figure 40), or to detect it through a loss of macrotexture, friction testing will a more 

reliable indicator of aggregate polishing issues. 

• Delamination—Delamination is the separation of the HFST from the underlying 

pavement due to a lack of bond to the underlying surface. Condition surveys may not 

detect delamination until the HFST begins to peel away (figure 39 and figure 48). 

Sounding techniques, however, can help identify delaminated areas during a project-level 

survey if delamination has been observed and there is suspicion of additional 

delamination. 

• Discoloration—Discoloration of HFST is not necessarily a problem but may indicate 

the presence of moisture trapped beneath the HFST (figure 41) or possibly some issue 

with the resin binder (figure 44 and figure 45). A project-level assessment can help to 

determine whether discoloration is indicative of other issues. 

7.3 REMOVAL AND REPLACEMENT 

HFST removal may be necessary due to premature failure of the treatment, replacement of the 

treatment once it has reached the end of its useful life, or as part of capital improvement for 

the roadway (e.g., repaving).

Milling or cold planing is the most common method for removal of HFST. If only the HFST is to 

be removed and not the underlying pavement, micromilling is preferred. It is important to 

protect the integrity of the underlying pavement if it will remain in place or if HFST will be 

reapplied. Micromilling tends to be less destructive to underlying asphalt and concrete than 

standard milling. Diamond grinding is another option for removal, and may be more appropriate 

for concrete than milling, but tends to be a slower and more costly process. 
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Note that while it may appear that all HFST has been removed, it is possible that residual resin

binder still remains in the pore structure of the underlying pavement left in place. This may 

inhibit the bond of any new HFST installed over the same surface as there is reduced 

opportunity for the resin binder to “soak into” the pavement surface. A simple test to 

determine if there is residual resin binder is to pour water on the surface. If the water beads or 

pools on the surface and does not soak into the pavement, there may be residual resin binder. 

If the water soaks into the pavement surface, the resin binder has likely all been removed. If 

resin binder remains, it should be removed to the greatest extent possible using techniques 

such as shotblasting.

When removing HFST along with the underlying pavement, there have not been any reported 

issues with the HFST being blended with asphalt millings. However, if the asphalt is to be 

recycled for a surface-grade asphalt pavement, it may be preferred to mill the HFST off first, 

separately from the asphalt. 

If HFST is to be reapplied, installation should follow similar practices to those outlined for a 

new treatment in previous chapters. If applied to the existing surface, special attention should 

be given to the integrity and macrotexture of the surface, particularly after milling. If milling led 

to raveling or other distresses in the remaining the surface, this should be repaired prior to 

placing new HFST. Note also that milling processes generate substantial dust and laitance, so 

special attention should be given to removing this latent dust with a compressed air wash. 
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CHAPTER 8—COST ESTIMATION AND FUNDING 

This chapter will discuss the cost of HFST and B/C estimation based on crash reduction 

benefits. Additional discussion is provided on potential options for funding HFST 

implementation. 

8.1 HFST COST 

HFST cost (unit cost, installed) has traditionally been highly variable due to a number of factors 

related to agency contracting mechanisms, materials, and installation. 

Figure 53 shows a generalized breakdown of the unit cost of HFST. Installation (mobilization, 

labor, etc.) accounts for roughly half of the unit cost, while the materials account for the other 

half. Of the material costs, resin binder accounts for roughly two-thirds of the material cost and 

aggregate one-third. 

Materials—Material prices (and associated supply volatility), are a key factor, particularly for 

calcined bauxite aggregate which is normally imported (although domestic suppliers are now 

available) and resin binder which is a specialty material with a limited number of suppliers. 

While the cost of imported calcined bauxite aggregate is often thought to be the primary 

contributor to materials cost, this is not necessarily the 

case.

Installation—Installation-related factors that affect HFST 

cost include the size of a given project, project 

requirements, and the contracting mechanisms. Economies 

of scale can significantly impact unit cost, and in general 

the larger a project (which may consist of several HFST 

installation locations), the lower the unit cost. The 

proximity of HFST installations to one another under a 

given project will also affect cost, as will any restrictions 

on scheduling of installation (e.g., seasonal or nighttime or 

weekend only work). Many agencies will let projects with 

multiple installations bundled together by District/Region 

or county to reduce cost (Wilson and Saca 2021). Some 

agencies have set up on-call master agreements with 

negotiated fixed costs for HFST installation on an asneeded basis. Specification requirements can be another 

factor impacting cost as requirements for traffic control, installation methods, surface 

preparation, materials testing, and finished product testing outlined in project specifications can 

all impact HFST cost. Contracting mechanisms and availability of competition is another factor. 

Agencies with multiple bidders will typically see more favorable unit prices, and projects where 

HFST installers are able to bid the work directly, rather than as a subcontractor to a general 

contractor, will generally be lower in cost. 

Source: FHWA

Figure 53. Graphic. 

Approximate breakdown of 

HFST cost (Atkinson et al. 

2016).
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Current unit prices for HFST used by agencies for project estimation purposes range from $20 

to $37 per square yard for the treatment itself (FDOT 2021, Wilson and Saca 2021). A 2018 

PennDOT study of 47 locations (from 7 different contracts) in the State revealed a total unit 

cost just over $36/SY which included materials and installation costs, inspection costs, and 

construction survey costs. This was for an average area of 1,805 SY per location which equates 

to approximately 680 ft treatment length for two lanes (Hershock 2020). FDOT reports a 

comprehensive HFST unit cost, which includes all related construction costs, ranging from $36

to $113/SY, with an average of $59/SY (FDOT 2021). As usage of HFST continues to grow, 

material costs are likely to continue to decrease, and more installers will likely enter the market 

thereby also decreasing installation cost. 

8.2 B/C RATIOS 

Published B/C ratios for HFST vary widely, based primarily on the process used for site 

selection. HFST used at very high crash locations (e.g., Wisconsin and California examples from 

chapter 1), particularly locations with high percentages of injury or fatal crashes will produce 

very high B/C ratios. Conversely, HFST deployed through a systemic implementation will likely 

produce very low B/C ratios, particularly if the site selection is risk-based and the B/C analysis 

is based on observed crashes, as there is typically a high cost to deploy the treatment on a large 

scale to prevent crashes which are spread over a large area. To refine B/C estimates for both 

site-specific and systemic-based HFST installations, there is an opportunity to employ the EB 

method to serve as the basis for the benefit analysis. 

PennDOT closely tracks project costs and regularly computes B/C ratios for HFST. From a 

2018 evaluation of 47 locations which had been in place for 3 to 5 years, PennDOT reported a 

B/C of 14.28 for all crashes and 8.97 for wet road crashes using crash costs associated with the 

KABCO scale, and 5.5 for all crashes and 2.04 for wet road when just considering fatal and 

various levels of injury crashes (PennDOT 2018; Hershock 2020). This is perhaps the most 

granular B/C ratio evaluation as PennDOT used actual HFST cost data for the analysis. 

KYTC documents HFST B/C ratios on an annual basis in the HSIP Annual Report. While initial 

years revealed very promising B/C ratios from 9 to 44, after 2 years of lower B/C ratios (less 

than 4), KYTC reevaluated their site selection process to ensure that non-friction-related 

crashes were filtered out for the network screening. This refinement of their site selection 

process has led to B/C > 30 for the past 2 years. 

FDOT has reported an average 5-year B/C ratio of 24.5 on tight curves using the KABCO 

method, but no calculable B/C for wide curves and intersections (FDOT 2021). 

Louisiana DOTD, which implemented a systemic deployment reported a B/C ratio of 0.5. This 

is not entirely unexpected for systemic deployment of HFST as the crash reduction benefits 

may take many years to be fully realized and Louisiana DOTD analysis is based on less than 3 

years of after period crash data.
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The FHWA study on CMFs for HFST reported B/C ratios for HFST for curve and ramp 

locations based on treatments in six States. Using an assumed conservative unit cost of $35/SY 

for HFST, and very conservative service life of five years, B/C ratios ranged from 6.00 for 

curves to 18.74 for ramps based on the crash reduction computed from an EB before-after 

evaluation (Merritt et al. 2020b). Actual B/Cs for many of these locations would likely be much 

higher with a lower unit cost and longer service life. 

B/C ratios should ideally be calculated using the most accurate cost data available, preferably 

actual cost data if the evaluation is performed on a project already in place. Crash costs, 

likewise, should be calculated based on the most accurate crash data which differentiates fatal, 

injury (including various levels of injury crashes), and property damage only crashes. If an agency 

does not have defined crash unit costs, national crash unit costs (based on KABCO scale) are 

available (Harmon et al. 2018). Realistic service life estimates should also be used, particularly 

when comparing HFST to an alternative countermeasure. As discussed previously, a service life 

of at least 7 to 10 years can be expected from a properly installed HFST. 

Tools such as FHWA’s Highway Safety Benefit-Cost Analysis spreadsheet and TCMS program 

(Pratt et al. 2018a) can be used for B/C ratio computation. The TCMS tool will compute B/C 

ratios specifically for different types of friction treatment on curves, including HFST, using 

predictive models for crash frequency based on change in pavement friction. As with any 

evaluation, B/C ratios should be continually verified with actual performance data and refined as 

needed. 

8.3 FUNDING 

HFST qualifies for Federal funding under the HSIP, which is geared toward reducing fatalities 

and serious injuries on all public roads. Historically, FHWA has matched HFST project costs 

through a 90/10 split utilizing HSIP funds. While each State’s process varies, local agencies can 

apply to receive funding for HFST projects within their jurisdiction.
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CHAPTER 9—CONCLUSION 

HFST is a highly-effective safety countermeasure for reducing both wet and dry friction-related 

crashes. When applied at appropriately selected locations and installed properly, exceptional 

B/C ratios can be realized. The majority of HFST installations are on curves and ramps, but a 

number of agencies are also implementing HFST at intersection locations. Summarized below 

are key practices based on successful implementation of HFST in the United States. 

Site Selection—Site-specific (crash history) approaches to site selection will provide the most 

immediate benefit in terms of crash reduction. However, systemic deployment of HFST should 

also be considered as a necessary strategy to help address the rare and random friction-related 

crashes on rural roadways. Predictive methodologies using SPFs and EB, and margin-of-safety 

analysis are data-driven methods for site selection which are readily available. Several highquality CMFs are available for curve and ramp HFST sites. Verification of candidate locations 

through field reviews and friction testing will help ensure HFST is applied at appropriate 

locations and that all issues related to project design and cost are addressed. 

Materials and Specifications—There is an excellent understanding of HFST material 

properties that will help ensure long-term performance. Critical properties of polymer resin 

binders have been identified and research continues to improve and establish appropriate limits 

for these properties. Although many alternative aggregate materials have been evaluated, only 

calcined bauxite has a demonstrated track record of providing exceptional skid resistance, 

maintained over the life of the HFST. AASHTO as well as a number of agencies with mature 

HFST programs have developed specifications which others can use as guidance to develop a 

specification. 

Installation and Inspection—There is an excellent understanding of HFST installation 

practices and inspection procedures that will help to eliminate premature failure of HFST due

to improper installation. Training of inspectors is a key element to a successful installation. 

Performance Monitoring—HFST performance should be continually monitored through 

regular evaluations of safety performance, regular friction testing, and regular monitoring of 

treatment condition. Performance monitoring will help agencies further refine site selection 

processes and installation specifications. PFMPs are an important tool for HFST deployment as 

they can help identify areas of deficient friction such that they can be treated proactively before 

crashes occur, as well as to monitor HFST friction performance over time. 

The agencies which have realized the greatest benefit from HFST deployment as a safety 

countermeasure: 

• Utilize data-driven approaches for HFST site selection. These data-driven approaches 

utilize statistically rigorous predictive methodologies such as SPFs and EB to identify and 

prioritize treatment locations. 

• Perform friction testing and project-level reviews of candidate installation locations to 

ensure each location is suitable for installation. 
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• Bundle multiple installations in a single contract and/or utilize on-call contracting 

mechanisms to reduce unit cost of deployment. 

• Require the use of advanced installation methods such as fully-automated systems to 

ensure proper conditioning, proportioning, and blending of resin binder materials, 

uniform application of resin binder to the specified mil thickness, and timely and uniform 

application of aggregate to the resin binder. 

• Continually monitor the performance of existing installations to document both safety 

performance and functional performance for the purposes of improving deployment 

programs. 

• Regularly review and update the B/C ratio of existing HFST installations for the purpose 

of improving the efficiency of HFST deployment.

• Regularly review and revise as needed the site selection practices as well as materials 

and installation specifications to continue to optimize deployment of HFST.

• Do not compromise on HFST material quality or performance requirements for the 

sake of reducing cost. 
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CHAPTER 10—ADDITIONAL RESOURCES

FHWA Frequently Asked Questions for HFST

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

hfst_faqs/

FHWA Technical Advisory for Pavement Friction Management 

(T 5040.38)

https://www.fhwa.dot.gov/pavement/t504038.cfm

FHWA Office of Safety HFST website

https://safety.fhwa.dot.gov/roadway_dept/pavement_friction/high_friction/ 
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FHWA/ATSSA Videos

6 min. version: https://www.youtube.com/watch?v=HVzS-VkABPE

20 min. version: https://www.youtube.com/watch?v=V860pC6ncAY

ATSSA HFST Technical Services 

https://www.atssa.com/Technical-Services/High-Friction-Surface-Treatment

ATSSA HFST Inspection and Installation Training Course

https://www.atssa.com/Training/Find-a-Course/High-Friction-SurfaceTreatment-Inspection-and-Installation#/qbeld/Web_HFS_Events

Pennsylvania DOT HFST Videos

https://www.youtube.com/watch?v=YE5N8WiAp24

https://www.youtube.com/watch?v=Sn34DAynjCE
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Oklahoma DOT HFST Video

https://www.youtube.com/watch?v=gWajb4Vz38Q

Florida DOT High Friction Surface Treatment Guidelines 

https://www.fdot.gov/docs/defaultsource/materials/pavement/performance/ndt/documents/hfstguidelines.pdf 
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APPENDIX A: OTHER POTENTIAL HFST APPLICATIONS 

Summarized below are some non-conventional but viable applications for HFST. Case studies 

are also highlighted for these applications when available. 

HFST AS AN ALTERNATIVE TO GEOMETRIC MODIFICATIONS

Friction demand can be reduced with roadway geometric modification such as increasing 

superelevation or reducing curve radius. However, these modifications may be cost prohibitive 

or not even possible due to site constraints (environmental restrictions, right-of-way 

limitations, etc.). HFST offers a lower-cost solution for increasing pavement friction supply to 

counteract higher friction demand at these locations. 

In 2012 Caltrans installed HFST on a curve along US 199 in Del Norte County as an alternative 

to curve realignment after they had not seen the desired crash reduction from multiple safety 

countermeasures (figure 54). Installation of HFST saved at least 2 to 5 years of total project 

time which would have been required for curve realignment (due to design and environmental 

review), saved nearly 6 months of construction time (along with a 100 mile detour during 

construction), and potentially saved nearly $14 million in total project cost. Crashes decreased 

from approximately nine crashes per year to no crashes since installation (FHWA 2015). 

Source: FHWA

Figure 54. Photograph. Example of HFST as an alternative to curve realignment

(FHWA 2015). 
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HFST AS AN ALTERNATIVE TO INCREASED ROADSIDE CLEAR ZONES

Roadside clear zones help to reduce crash severity or the consequences of RwD crashes. Tree 

removal is a common requirement in increase clear zones. However, environmental concerns 

may not allow for tree removal at all locations. HFST provides a lower-cost treatment that can 

help to prevent RwD crashes and the associated consequences from roadside obstacles at 

these locations. 

PennDOT used HFST for this particular application after they determined it was not possible to 

remove mature, culturally-significant trees that were contributing to crashes due to shielding of 

the roadway along Route 147 in Dauphin County. HFST was applied to help keep vehicles on 

the roadway, rather than removing the trees. In the 4 years since HFST was applied, fatal and 

injury crashes were completely eliminated. 

HFST FOR TANGENT APPLICATIONS

In some instances, HFST may be a solution to inadequate friction on tangent roadway sections. 

In Illinois, for example, a tangent section of Interstate 74 had a very high percentage (77 

percent) of RwD crashes highway, with more than 50 percent being tractor trailer semis, and 

more than 50 percent of the crashes occurring under wet conditions. Illinois DOT determined 

that high crosswinds were causing semi-trucks to lose control, and inadequate pavement 

friction reduced the ability of these vehicles to regain control. HFST was applied to this tangent 

section of interstate, dramatically reducing crashes. In the five years prior to HFST application, 

there were eight passenger vehicle and 50 tractor trailer semi-truck crashes involving slick 

pavement and/or strong crosswinds. In the nearly four years following HFST application, there 

were six passenger vehicle crashes but zero tractor trailer crashes involving slick pavements 

and/or wind.

HFST FOR TUNNELS

Tunnels offer little margin for error for RwD crashes, and HFST offers a solution to help keep 

vehicles in their lane. While wet-weather crashes would not be expected in a tunnel unless a 

drainage problem existed, a decrease in friction over time would not be unexpected as oil and 

rubber deposits that are normally washed away with precipitation will continue to accumulate 

unless the surface is regularly washed. While there is no published information on the benefits 

of HFST for crash reduction in tunnels, a noted benefit of a buff-colored calcined bauxite used 

for HFST in tunnels in Germany is improved visibility in tunnels due to the lighter-colored 

pavement surface reflecting vehicle and tunnel lighting (figure 55 and figure 56). 
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© The Transtec Group

Figure 55. Photograph. Example of HFST used for tunnel application. 

© The Transtec Group 

Figure 56. Photograph. Example of light reflectance off of a light-colored HFST 

tunnel. 

HFST FOR STEEP GRADES

Steep downhill grades, particularly at intersection approaches are key applications with high 

friction demand. The City of Bellevue, Washington applied HFST to a curved downhill 

intersection approach in 2004 to reduce crashes attributed to grade, skidding, and driving too 

fast for conditions (figure 57). After applying HFST, crashes decreased by 78 percent and costs 

associated with crashes by 83 percent (FHWA 2016). 
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Figure 57. Photograph. HFST application for steep grade at intersection approach 

(FHWA 2016).

Source: FHWA

COLORED SURFACES

Colored pavement surfaces are another application where HFST or a similar thin polymer 

overlay can be utilized. Colored pavement surfaces are typically used for demarcation purposes

and may require FHWA approval if used for an application not included in the Manual of 

Uniform Traffic Control Devices (MUTCD). Depending on the application, these surfaces may 

or may not have the same level of friction demand as typical HFST applications for curves, 

ramps, and intersections. To achieve the desired color, tinted resin binder and/or dyed 

aggregate can be used, or alternatively, aggregates with natural coloration (e.g., red granite).

Resin binder materials and installation methods are generally similar to conventional HFST, with 

the exception of overlay materials where the resin binder and aggregate are mixed together 

before application. Color-fastness of these surfaces under UV exposure is critical for ensuring 

they will continue to provide the intended demarcation over the life of the treatment. Some 

examples colored surface applications include:

• Lane Demarcation (figure 58 thru figure 62) 

• Bicycle Lanes (figure 63) 

• Pedestrian Crossings (figure 61) 

• Railroad Crossings (figure 64) 
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© Traffic Calming USA

Figure 58. Photograph. Lane demarcation with two colors of polymer overlay.

© The Transtec Group

Figure 59. Photograph. Example of HFST used for demarcation at an intersection 

approach. 
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© Traffic Calming USA

Figure 60. Photograph. Example of HFST used for bus lane demarcation. 

© Traffic Calming USA

Figure 61. Photograph. Example of HFST used for pedestrian crossing. 
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© Traffic Calming USA

Figure 62. Photograph. Example of HFST used for roundabout demarcation. 

© DBi

Figure 63. Photograph. Green bicycle lane application.
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© Traffic Calming USA

Figure 64. Photograph. Railroad crossing application.

Bridge decks were the original application for HFST in the United States, dating back to the 

1950s (Cheung and Julian 2016). Typically referred to as thin or multi-layer polymer overlays or 

broom and seed overlays, applications to bridge decks serve two purposes: to seal and 

preserve bridge decks from chloride ingress, and to increase friction on surfaces which will 

freeze before the surrounding pavement in colder climates. Bridge decks are not necessarily 

considered locations with high friction demand, unless they are part of a curved ramp or 

overpass. As such, the frictional properties are less critical for this application and alternative 

aggregates such as flint, granite, taconite, slag, etc. are typically used. However, the resin binder 

materials and processes used to apply bridge deck overlays are the same. It is not uncommon 

for a double-layer application to be used as well (figure 65). 

© The Transtec Group

Figure 65. Photograph. Manual application of HFST to bridge deck.
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STEEL PLATE TRENCH COVERS

Steel plates used to cover trenches from utility cuts in the pavement surface can be very slick, 

particularly in wet conditions. Many times, these plates are used in or near intersections where 

friction demand is high with vehicle braking. Many agencies require that these plates have a skidresistant surface. The New York City DOT, for example, specifically requires that, “All plating 

and decking shall have a skid-resistant surface equal to or greater than the adjacent existing 

street or roadway surface. The whole surface area of all plating and decking must be skidresistant.” (NYCDOT 2019). MoDOT, likewise, requires that steel plates used for trench 

covers be treated for skid resistance using either surface deformation or from a friction course 

(MoDOT 2021). 

While there are no known studies on safety impacts of skid resistant surfaces on trench plates, 

HFST provides a simple solution. Most common HFST resin binder materials should adhere 

well to properly prepared (e.g., sandblast/shotblast) steel plates (figure 66). 

© Heaton Manufacturing 

Figure 66. Photograph. HFST with calcined bauxite on steel trench plates (Heaton 

Manufacturing n.d.). 
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APPENDIX B: EXAMPLES OF SYSTEMIC DEPLOYMENT OF 

HFST

Four examples of criteria used for systemic deployment of HFST are described below. It should 

be noted that most agencies will typically apply more than one countermeasure at these 

locations. As such, an evaluation of the effectiveness of HFST (by itself) in reducing rural 

roadway curve crashes can be very difficult. 

LOUISIANA

Louisiana DOTD used a statewide systemic approach for HFST deployment beginning in 2015. 

The target roadway classification was two-lane rural roads which accounted for 43 percent of 

fatalities from 2010 to 2012 and the target crash type was RwD crashes which accounted for 

nearly 90 percent of the fatalities (McRae 2020). Risk factors identified for site selection 

included: 

• Traffic (AADT): 2,500 to 7,500 vehicles per day. 

• Lane width: 12 ft or greater. 

• Shoulder width: 2 to 6 ft. 

• Degree of curvature: > 3.5 (radius < 1,640 ft). 

Based on these criteria, 282 curves were initially identified statewide for safety improvements 

including HFST and other low-cost countermeasures. HFST was ultimately installed on roughly 

150 curves statewide, playing a key role in countermeasure deployment. A formal before-after 

analysis has not yet been completed to assess the effectiveness of this approach with respect to 

crash reduction. 

GEORGIA

Georgia DOT used a systemic approach to HFST deployment beginning in 2014. Georgia 

DOT’s two-step process began with identification of roadway corridors with a high number of 

segments with a high severity index which represents the average damage (based on fatal and 

serious injury crashes) resulting from crashes along the corridor. The second step was to 

collect ball bank measurements (at posted speed) on all curves along the selected corridor 

segments, and to identify any curve with a BBI value greater than 12 for treatment (Tsai et al.

2018). The majority of corridors selected for HFST installation through this process were rural 

two-lane roads. 

Georgia DOT is currently refining their site selection process, moving away from a systemic 

process using BBI values towards a more systemic data-driven process utilizing automated 

roadway data collection methods to identify HFST candidates based on roadway characteristics. 

A thorough before-after analysis of Georgia DOT’s initial systemic deployment of HFST has not 

yet been completed. 
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THURSTON COUNTY

Thurston County in Washington State utilized a systemic approach to HFST deployment for 

reducing RwD crashes on local roads. HFST candidate sites were identified from 0.2-mile 

roadway sections with more than three skidding/out-of-control crashes under wet and icy 

conditions. Risk factors were used to rank candidate sites for potential treatment, and included 

(Torbic et al. 2020, Tsai et al. 2018): 

• Roadway class: arterial and collector roads. 

• Posted speed of 50 mph. 

• Traffic volume of 5,000 to 8,000 AADT (high confidence), 3,000 to 5,000 AADT (low 

confidence). 

• Paved shoulders 4 or 8 ft in width or native shoulders of 2, 3, 7, or 8 ft in width,

• Presence of a vertical curve. 

• Consecutive horizontal curves. 

• Speed differential between posted speed and curve advisory speed of 0, 5, and 10 mph. 

• Presence of a visual trap (i.e., a minor road on the tangent extended).

DELAWARE

Delaware DOT implemented a systemic site selection process after a successful HFST 

demonstration project in 2013. Delaware DOT used this process to address RwD crashes 

which accounted for 47 percent of all fatal crashes. The target roadway classification was 

collector and local roadways and the target crash type was wet weather RwD crashes at 

curves. For the initial installation, Delaware treated 15 high crash curves. In 2016, Delaware 

treated an additional eight locations. Preliminary results from these 23 locations indicated that 

RwD crashes decreased at 83 percent of the locations by an overall average of 56 percent 

(Americas Transportation Awards n.d.).

 
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APPENDIX C: HFST INSPECTION CHECKLIST

Item Item description Status

1. Pre-Construction

1.1

Review contractor Quality Control Plan (QCP) to verify requirements for:

a) Test strip and full-scale/production of HFST placement schedule (if test strip is to 

be completed separately).

b) Description of equipment for placing HFST.

c) Methods for conditioning, metering, blending, and applying resin binder.

d) Methods for applying aggregate, including timing of placement onto resin binder.

e) Methods for monitoring and documenting material usage. 

f) Method for protecting areas that will not receive HFST.

g) Description of acceptable environmental conditions (temperature and 

precipitation) for placing HFST.

h) Cure time and time to opening to traffic estimates for HFST.

i) Storage and handling of HFST materials.

j) Disposal and recycling of excess HFST and containers.

k) Contingency plan for possible failure during the HFST application.

l) Name of the certified independent testing laboratory.

m) Key personnel and contact information.

n) All project certifications and test results.

1.2 Verify name and contact information for contractor QCP administrator.

1.3 Check that materials supplied to the project meet specification requirements (through 

agency testing or from certified test results from the installer).

1.4 Verify that a resin binder manufacturer’s representative is present for initial/test strip 

installation. 

2. Materials

2.1 Check that resin binder is type and brand specified in the QCP.

2.2 Check that aggregate material is type and brand specified in QCP.

2.3 For reclaimed aggregate only: verify that reclaimed material had been blended with 

new/virgin material at the specified ratio (e.g., two parts new to one part reclaimed). 

2.4 Check resin binder and aggregate stockpiles to verify proper packaging and storage of 

materials.

2.5 Check that aggregate is clean (minimal dust content and no foreign materials) and dry 

(subjective assessment). 

2.6 Check that adequate quantities of resin binder and aggregate materials for the 

intended installation area are on-site or accessible near the project site. 

2.7 Sample materials for verification testing on-site as required by specification.
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Item Item description Status

3. Surface Preparation

3.1 Check that all distresses identified for pre-treatment in the project plans have been 

addressed. 

3.2 Check that all striping and pavement markings have been removed or masked as 

required in project plans and specifications.

3.3 Check that all drainage inlets, manhole and valve covers, and other utilities and 

structures have been masked as required in project plans and specifications.

3.4 Shotblasting: Verify that surface has been shotblast to concrete surface profile (CSP) 

of 5, as required in project specifications, followed by compressed air wash.

3.5 Check that entire surface has been cleaned with a mechanical sweeper and/or a 

compressed air wash as required in the project plans.

3.6

Check that all pavement surfaces to be covered with HFST are dry and free of oils, 

grease, dust (including latent dust from shotblasting) and foreign material prior to 

HFST placement.

4. Pre-Application

4.1 Verify test strip placement procedure (i.e., separate test strip or as part of initial 

production installation).

4.2 Check that equipment for placing HFST is as outlined in the QCP.

4.3 Document width of placement based on installation vehicle setup.

4.4 Check for masked-off areas at beginning and end of placement to ensure clean 

termination joints.

4.5 Verify that resin binder metering devices are fully functional.

4.6 Document ambient and surface temperatures at start and end of application 

(minimum) and routinely throughout application if necessary. 

5. Resin Binder Application

5.1 Check for changes in coloration and consistency of resin binder throughout 

application.

5.2 Check uniformity of resin binder film across the lane (e.g., no gaps or tearing of the 

film or variations in thickness).

5.3 Check thickness of resin binder on pavement surface as it is placed using a mil 

thickness gage as required in project specifications.
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Item Item description Status

5.4

Document total quantity of material used from metering devices on installation 

vehicle. Verify if quantity of material used corresponds to anticipated quantity based 

on placement area and mil thickness requirement.

5.5

Manual application of small areas:

a) Check that resin binder is properly proportioned and thoroughly blended before 

being deposited on pavement surface.

b) Check that resin binder is spread with notched squeegees to the required, 

uniform thickness over the placement area.

c) Check that resin binder is not sheeting or running across the lane or down the 

pavement grade before aggregate is applied.

d) Check that no foot traffic other than spiked shoes are allowed on uncovered 

resin binder.

5.6 Check that no vehicular traffic is allowed onto the surface prior to curing of the resin 

binder.

6. Aggregate Application

6.1 Check that aggregate is applied onto the resin binder within the time required in the 

project specifications.

6.2 Check that aggregate is applied in a manner that it does not disturb the resin binder

6.3 Check for dryness and cleanliness (substantially free of dust and foreign matter) of 

aggregate as it is deposited.

6.4 Check for uniformity of placement across the lane.

6.5 Check for aggregate placement until refusal over resin binder.

6.6 Check that any exposed resin binder and “wet” areas that appear are covered.

6.7 Document total quantity of material used from installer records. Verify if quantity of 

material used corresponds to anticipated quantity based on placement area.

6.8

Manual Placement of small areas:

a) Check that aggregate is deposited onto the exposed resin binder within the time 

required in the project specifications.

b) Check that aggregate is broadcast such that it does not disturb the resin binder.

7. Aggregate Removal

7.1 Check that resin binder has reached adequate cure prior to sweeping (verify that resin 

binder is not soft and that aggregate does not pull out of resin binder).

7.2 Document timing of aggregate removal with respect to completion of HFST 

placement.
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Item Item description Status

7.3 Check that aggregate removal using a vacuum or power brooms is not damaging the 

HFST surface and exposing the underlying pavement.

7.4 Check that surface is free of loose aggregate after completion of all aggregate removal.

7.5 Check for and document any areas where underlying pavement is exposed after 

aggregate removal.

8. Opening to Traffic and Acceptance Testing

8.1 Check for any remaining loose aggregate.

8.2 Check for any “soft” areas in the HFST surface where resin binder may not have fully 

cured.

8.3 Check for and document any discolored areas in HFST surface.

8.4 Check for and document any areas where HFST is missing and needs to be patched.

8.5 Check for replacement of pavement markings (temporary or permanent) as required 

in the project plans and specifications.

8.6 Verify that masking has been removed from drainage inlets, manhole and valve covers.

8.7 Check for loose aggregate on any adjacent untreated lanes and paved shoulders, and 

untreated pavement before and after the treated area.

8.8 Verify the plan for acceptance testing and check that acceptance testing is performed 

in accordance with project specifications. 

8.9 Check acceptance testing result for conformance with specification requirements. 

9. Post-Installation

9.1

Monitor aggregate shedding over the first several days after installation and note any 

excessive build-up of loose aggregate within the treated lanes or on adjacent surfaces. 

Ensure loose aggregate is promptly removed if it presents a safety hazard.

9.2 Check that surface is re-swept within two weeks after initial placement to remove 

loose aggregate.

9.3 Monitor the HFST surface for discoloration, delamination, cracking, and other 

distresses.
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