1 | P a g e

Noteworthy Practice:

HFST Institutionalized at PennDOT

Pennsylvania Advances High Friction Surface Treatment (HFST)

In Pennsylvania, over 50% of the fatal and serious injury crashes involve a lane departure, and intersection crashes account for 21%

of the annual fatalities and 30% of serious injuries1. Slippery and wet roads often contribute to many of the fatal and serious injury 

crashes in Pennsylvania. To reduce wet-pavement crashes at curves and intersections throughout the Commonwealth, the 

Pennsylvania Department of Transportation (PennDOT) has been installing high friction surface treatments (HFSTs) at strategic 

locations. A HFST is a safety countermeasure intended to restore and maintain pavement friction in wet and dry conditions to 

reduce crashes. This treatment is especially effective where there is a history of wet-pavement crashes.

How Do HFSTs Work?

Where drivers brake excessively (e.g., going around curves, on steep downgrades, or 

approaching intersections), the road surface can become polished, reducing the available 

pavement friction. Reduced pavement friction may contribute to vehicles losing control,

skidding, or hydroplaning when they speed, turn abruptly, or brake excessively. With

HFSTs, a thin layer of calcined bauxite aggregate provides increased friction to the

pavement surface and makes the pavement more resistant to wear and polishing. HFSTs

help vehicles maintain their lane as they traverse around curves and allows drivers to stop

within reasonable distances at intersections, resulting in safer roads for the traveling 

public. Figure 1 illustrates the physical difference between a normal pavement surface

and a surface treated with a HFST.

PennDOT’s Approach to Implementation

In 2007, PennDOT installed its first HFST at a high-crash location along State 

Route 611 in Northampton County (District 5) (see Figure 2). The treatment was 

applied at a sharp horizontal curve on a rural two-lane road with 9-ft travel lanes 

and no shoulders. The roadside on one side was a steep cliff, and on the other 

side was a steep drop-off. In the 10 years prior to installation of the HFST, 20 wetpavement-related crashes occurred at the site. Over the years, PennDOT had 

tried other treatments (e.g., chevrons, advanced warning signs, centerline rumble 

strips) without much success in reducing the frequency of wet-pavement 

crashes2.

1 Pennsylvania Department of Transportatation. Pennsylvania Strategic Highway Safety Plan, 2017.

2

State Transportation Innovation Council. 2015 Fact Sheet - High Friction Surface Treatment, 2015.

Figure 1: Boundary between Normal and 

HFST Pavement Surfaces. Source: PennDOT

 Normal HFST

Figure 2: HFST Pilot Project. Source: PennDOT
2 | P a g e

Following a series of skid tests and an analysis of the crash data over the next few years, the pilot project proved successful. In the 

first five years following installation of the HFST at the pilot project location, zero wet-pavement-related crashes occurred. While 

PennDOT evaluated the performance of the HFST pilot project, numerous wet-pavement crashes continued to occur at other 

locations throughout the state.

Based on the success of the pilot project, PennDOT added HFST to its approved materials listing and 

developed specifications for installation of the treatment (now in the fourth version of specifications)3

(see Figure 3). Then, in 2012, PennDOT District 5 applied the treatment to 13 additional sites 

experiencing a high frequency of wet-pavement crashes. In addition, HFSTs were included as one of the 

potential countermeasures for consideration within the Pennsylvania Roadway Departure Safety 

Implementation Plan 4, prepared in conjunction with the Federal Highway Administration (FHWA) 

Roadway Departure Team. In the Pennsylvania Roadway Departure Safety Implementation 

Plan, the initiative called for the systemic deployment of relatively low-cost, cost-effective

countermeasures at many targeted locations with a frequency of roadway departure crashes. 

HFSTs were to be considered as a means of reducing wet-pavement crashes when deployed along rural and urban tangent and 

curved sections of highway and intersection approaches. Figure 4 illustrates three types of locations where PennDOT has installed 

HFSTs.

The primary steps and schedule for implementation of HFST through the roadway departure plan involved:

1. The Safety Management Office working with Design, Maintenance, and District Offices to develop guidelines for use of the 

micro-textures and epoxies to be applied on the sections of highway with high incidences of wet-pavement crashes,

2. Conducting skid testing at the potential locations to determine if low frictional characteristics may be contributing to the 

wet-pavement crashes, and

3. Determining the appropriateness of applying a HFST to the location.

Other factors that could potentially influence the decision to install HFST at a location included:

• Evidence of excessive braking at intersection approaches with running stop signs, running red light, and rear-end crashes.

• Inability to move fixed objects to increase the clear zone.

• Inability to make geometric changes to a curve with known crash history.

From 2012 to 2018, HFSTs were installed at approximately 44 new locations annually to reduce wet-pavement crashes. By 2018, 

HFSTs were installed at 305 locations throughout the Commonwealth, covering approximately 53.5 miles of roadway. In 2021, 

PennDOT estimates HFSTs have been installed at close to 500 to 600 locations. The treatment has been installed at curves and 

intersections on urban and rural two-lane and multilane roadways, including high-speed freeways. To streamline the project delivery 

process, PennDOT often bundled the safety contracts that were bid out districtwide or countywide. This helped the treatment to be

implemented more quickly throughout the district/county, and PennDOT realized a substantial cost savings. For example, when 

3 Pennslyvania Department of Transportation. Specifications. Publication 408, 2020.

4 Pennsylvania Roadway Departure Safety Implementation Plan, 2012.

https://www.penndot.gov/TravelInPA/Safety/Documents/PA%20Roadway%20Departure%20Safety%20Implementation%20Plan%20

(RDIP).pdf

Figure 3: Current Construction 

Specifications for PennDOT Projects

Figure 4: Types of Locations Where PennDOT Has Installed HFSTs. Source: PennDOT

Curves on Rural Two-Lane Roads Curves on Rural Multilane Roads Intersection Approaches
3 | P a g e

installed on an individual project basis, PennDOT found the cost of a HFST was approximately $36/square yard (SY); but when 

PennDOT HFST projects were bundled, the cost of a HFST was reduced to approximately $16/SY.

Safety Effectiveness and Economic Benefits 

Since the initial assessment of their pilot project, PennDOT has tracked the safety performance at many treatment sites and 

conducted several studies to estimate the safety effectiveness and economic benefits due to HFST applications in Pennsylvania:

• In 2016, based on an evaluation of 15 locations and an analysis of three years of before-after crash data and cost data, 

PennDOT estimated the benefit-cost ratio of HFSTs to be 20.5 to 15.

• Even though data were not sufficient to apply an advanced statistical assessment, in 2017, based on an extensive beforeafter study of 106 locations, PennDOT estimated that HFSTs reduced the number of roadway departure crashes by 74% at 

curves, and most importantly fatalities were reduced by 100%. The study results also showed the greatest reduction in 

crash frequency and severity and greatest return on investment occurred for intersections on horizontal curves in rural 

areas6.

• In 2018, based on an evaluation of 47 locations with up to five years of before-after crash data, PennDOT estimated that 

HFSTs resulted in a benefit-cost ratio of 5.50 for all crashes and 2.40 for wet-road crashes7.

PennDOT has also found HFSTs have year-round benefits, especially in the fall 

and winter. In the fall, when leaves fall onto the treated surface, the leaves

are practically ground away against the surface reducing the chance for 

vehicles to skid on wet leaves (see Figure 5). In the winter, HFSTs hold up well 

during snow plowing (i.e., PennDOT has not seen degradation of the material 

or decreased longevity due to plowing operations); and the treatment is 

effective at reducing crashes during icy, slushy, and snow-covered conditions.

Table 1 presents findings from a multistate study, published in 2020, based on 

curve treatment data for 95 sites in Pennsylvania, 36 sites in Kentucky, and 26 

sites in West Virginia. As shown in Table 1, the researchers developed crash 

modification factors (CMFs) using the Empirical Bayes before-after method 

and estimated a benefit-cost ratio associated with the safety effectiveness of 

HFSTs reducing crashes at curve locations8.

Table 1. Recommended Crash Modification Factors (CMFs) and Benefit-Cost Ratio for Installation of HFST at Curves8 

Crash Type

CMF

(95-percent Confidence Interval)

Benefit-Cost Ratio

(Sensitivity Range)

Total crashes 0.430 (0.375-0.485) 6.000 (3.360-8.450)

Injury crashes 0.515 (0.442-0.588) —

Run-off-road crashes 0.279 (0.216-0.342) —

Wet-road crashes 0.168 (0.485-0.897) —

Head-on plus opposite-direction sideswipe crashes 0.691 (0.485-0.897) —

Note: A dash denotes not applicable.

5

Federal Highway Administration. Northeast Roadway Departure Safety Peer Exchange, 2016.

https://rosap.ntl.bts.gov/view/dot/49575

6 Musey, K., M. Kares, S. Park, and G. Kennedy. Safety Impact of High-Friction Surface Treatment Installations In Pennsylvania,

Transportation Research Circular, Number E-C220, First International Roadside Safety Conference, San Francisco, CA, Transportaion.

Research Board, 2017. http://onlinepubs.trb.org/onlinepubs/circulars/ec220.pdf

7 Pennsylvania Department of Transportation. Highway Friction Surface Treatments in Pennsylvania, Keeping You on the Road.

https://www.tesc.psu.edu/assets/docs/high-friction-surface-treatments.pdf

8 Merritt, D.K., C.A. Lyon, and B.N. Persaud. Developing Crash-Modification Factors for High-Friction Surface Treatments. Report No. 

FHWA-HRT-20-061. Federal Highway Administration, 2020.

Figure 5: Benefits Experienced during the Fall. 

Source: PennDOT
4 | P a g e

Demonstrated Skid Resistance Qualities of HFST Sites

During the first few years as PennDOT was beginning to institutionalize 

the use of HFSTs, skid testing (see Figure 6) was conducted to monitor

the frictional performance of the treatment sites. Through this 

monitoring program, PennDOT found the HFST sites had average skid 

numbers over 70 when measured multiple years after installation of the 

treatment; whereas traditional pavement overlay initial skid numbers

normally ranged from 50 to 55 and declined into the 40s after a few years9.

HFST Installation Basics and Specifications

As PennDOT has been installing HFSTs at locations for many years, 

the Department has developed specifications for the installation of 

HFSTs in Pennsylvania. Basically, HFSTs are applied to an existing 

asphalt or concrete pavement surface. The pavement must be 

structurally sound. PennDOT requires a 30-day waiting period 

before a HFST can be applied to a new asphalt pavement and a 28-

day waiting period before applying the treatment to a new concrete 

pavement3.

At the beginning of the installation process, all pavement surfaces 

are prepared prior to installation of the HFST. All existing pavement 

markings and utilities (i.e., manholes/inlets) are covered and 

protected. The pavement surface is cleaned of all debris; washed 

with a mild detergent solution to remove oils, greases, and other 

deleterious material; rinsed with water; and dried using a hot 

compressed air lance. If cracks are present, loose material is 

removed; and cracks one-fourth inch or greater are filled with a 

resin binder. After the binder in the pre-treated cracks has gelled, 

the resin binder is applied to the pavement surface. Next, a thin 

layer of high-quality polish-resistant calcined bauxite aggregate is 

placed on top of the resin binder. After the binder treatment has 

cured and before opening the road to traffic, the travel lanes and 

shoulders are cleaned using a vacuum sweeper to reclaim surplus 

aggregate. The treatment is usually installed one lane at a time and 

takes about two to four hours to install per lane. Between 15- to 30-

days after placing the HFST, the site is again cleaned using a vacuum 

sweeper to reclaim loose aggregate.

PennDOT permits installation of HFST using three main application 

methods (see Figure 7): manual, semi-automated, and fullyautomated. Permissible application methods vary by size of the 

project and volume of the road (see Tables 2 and 3).

9

Federal Highway Administration. Pennsylvania SR611-Northampton County. Case Study – High Friction Surface Treatment. FHWASA-16-056. Federal Highway Administration, 2016.

Manual Application

Semi-Automated Application

Fully-Automated Application

Figure 6: Skid Testing Equipment. Source: PennDOT

Figure 7: Three Primary Application Methods. 

Source: PennDOT
5 | P a g e

 Table 2. Permissible Application Methods for Roads Under 25,000 ADT3

Site Size (Square Yards) Main Application Method

Less than 300

Hand Mixing and Manual Application, 

Semi-Automated Application, or

Fully-automated Application

300 or above

Semi-Automated Application, or

Fully-Automated Application

 Table 3. Permissible Application Methods for Roads of 25,000 ADT and Above3

Site Size (Square Yards) Main Application Method

Less than 300

Hand Mixing and Manual Application, 

Semi-Automated Application, or

Fully-Automated Application

300 to 1,500

Semi-Automated Application or

Fully-Automated Application

Larger than 1,500 Fully-Automated Application

The primary benefits of using the fully-automated application method versus the 

hand mixing and manual application method include10:

• Improved speed and quality resulting in reduced installation time.

• Consistent with proven specification.

• Reduced exposure of workers to live traffic.

• Full lane width (i.e., 12 ft) continuous operation in one pass.

• Less material component waste.

• Even application of binder and aggregate.

The primary disadvantage of the semi-automated application method

is the amount of dust that can be generated when spreading the

aggregate.

Bauxite vs Alternative, Non-Bauxite Aggregates11

The aggregate specified in PennDOT’s HFST specification is based on industry 

standards and requires a certain amount (87%) of the aggregate to be aluminum oxide 

(bauxite). Aluminum oxide is very abrasive and durable. Most bauxite is imported from 

overseas and can be relatively expensive.

Aggregates used in HFSTs are a hot topic, and many questions associated with these 

aggregates arise. For example, would lesser percentages of bauxite work satisfactorily? 

Are there other non-bauxite aggregates that perform just as well but are less 

expensive? After experimenting and evaluating the potential use of alternative 

aggregates (non-bauxite), PennDOT realized that the cost of the aggregate is relatively small compared to the cost of the epoxy; so 

using a less expensive aggregate will not save much money over the long term. In addition, if the durability of a less expensive 

aggregate is also less, the less expensive aggregate could cost more on a life-cycle basis. Therefore, PennDOT’s specifications require 

the use of clean, dry, high-friction bauxite aggregate3.

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

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

11 Pennsylvania Department of Transportation. Technology Insider. July 2017. 

Figure 8: Equipment Associated with 

Fully-Automated Application. Source: PennDOT

Figure 9: Boundary between HFST and Pavement Surface. 

Source: PennDOT

Figure 10: Aggregate Used in HFST. 

Source: PennDOT
6 | P a g e

Benefits of HFSTs12

The benefits of using HFSTs include:

• Reduces injury crashes on curves and intersections that exhibit a high 

propensity for wet-pavement-related crashes.

• Installs quickly with minimal impact on traffic (e.g., usually installed one lane 

at a time and takes about two to four hours to install per lane).

• Provides a durable, long-lasting, moderate-cost surface option over the 

pavement’s life cycle.

• Improves skid resistance.

• Decreases braking distance, hydroplaning, splash, and spray.

Lessons Learned

Based on their experience with HFSTs, PennDOT shared some lessons learned:

• HFST is a proven safety countermeasure and is suitable for all weather 

applications at strategic locations and can be deployed systemically.

• There are crashes that only HFSTs can mitigate. This treatment is working 

and is suitable for States that want to save lives at targeted locations.

• HFST should be installed on pavement in good structural condition. If the 

pavement is cracked, raveled, or rutted, the HFST will not last long.

• HFST should not be installed in cold weather. The treatment will not stick.

• If the wet road crashes are due to drainage issues where there is ponding 

water, HFST is not the solution. The drainage issue should be addressed first.

• In the fall when leaves, walnuts, apples, and other debris fall on the road and create slick surfaces, the HFST countered

these issues by helping to grind down the debris and maintain the skid resistance of the pavement surface.

• Installing HFST through a bundled project contract is the most economical process to install HSFT across the state [e.g., cost 

of HFST when installed on individual project basis ($36/SY) compared to cost when HFST projects are bundled ($16/SY)].

• Communicate with the county maintenance staff to make them aware of the locations where HFSTs are installed so 

treatments are not removed shortly after installation (e.g., one or two years) during resurfacing projects.

• Construction inspectors should coordinate installation dates of HFSTs with maintenance staff responsible for skid testing so 

skid testing can be conducted in a timely manner following installation of the treatments.

For Additional Information

For additional information about HFSTs contact Joseph Cheung, FHWA Office of Safety, at joseph.cheung@dot.gov. 

For additional information about the Pennsylvania Department of Transportation’s use and institutionalization of HFSTs, contact 

Jason Hershock, Pennsylvania Department of Transportation, at jhershock@pa.gov.

PennDOT created a website, a video, and other materials promoting the use of HFSTs. For more information, visit

https://www.penndot.gov/about-us/StateTransportationInnovationCouncil/Innovations/Pages/High-Friction-SurfaceTreatment.aspx

Publication Number FHWA-SA-21-127

12 Casadei, D. PennDOT District 10 Demos Benefits of High Friction Surface Treatment. PennDOT Way, 2018. 

https://www.penndot.gov/PennDOTWay/pages/Article.aspx?post=174

Figure 11: Typical HFST Application on 

Rural Two-Lane Road. Source: PennDOT

Figure 12: Typical HFST Application on 

Urban Freeway. Source: PennDOT