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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation
FHWA Highway Safety Programs

SECTION 1: Introduction

SECTION 1: Introduction

1.1. Background

Single and multi-vehicle crashes are the leading cause of fatalities and major injuries in the United States, particularly in rural areas. Roughly 25 to 50 percent of all fatal crashes occur at intersections or on horizontal curves.1,2 The probability of crashes during vehicle stopping and turning movements is influenced by the friction between the tires and pavement surface.

In horizontal curves, vehicle speed and curve geometry create a "friction demand" that can be higher than adjacent sections of road. Crashes can also occur at intersections when errors in driver judgment create an unexpected need for increased friction due to excessive speed, lateral movement, or both.

Highway safety starts with the driver's ability to control the vehicle. The combination of: 1) the judgment needed to negotiate a horizontal curve, 2) pavement surface wear, and 3) the higher friction demand of a vehicle moving through a horizontal curve compared to the rest of the road results in increased potential for crashes. Adequate surface characteristics, particularly for friction, at critical locations are an effective means to increase traffic safety and reduce crashes. Maintaining an appropriate level of friction is critical for safe driving. One low-cost approach that has been shown to be effective in addressing high "friction demand" locations is the installation of a High Friction Surface Treatment (HFST).

1.2 High Friction Surface Treatment Defined

HFSTs are pavement surface treatments with exceptional skid-resistant properties that are composed of extremely hard, polish and abrasion-resistant aggregates bonded to the pavement that greatly enhance the frictional characteristics of a road surface. The high-adhesive and tensile properties of the binder lock the aggregates in place. This creates a durable surface capable of providing long-lasting surface friction on road sections with high friction demands, such as those that experience excessive and heavy braking, contain sharp horizontal curves, or feature a vertical grade in combination with a horizontal curve.

HFSTs address two speed-related crash conditions: (1) where there is low to marginal friction (further reduced by weather), and (2) where the available friction is incompatible with approach speeds and roadway geometry (friction demand). In general, HFSTs assist in keeping vehicles in their lane around curves and allow vehicles to stop in shorter distances at intersections. For details on the HFST material requirements and test methods, the reader is referred to the list of references at the end of this document.

1.3 Kentucky Transportation Cabinet's High Friction Surface Treatment Program

Although multiple agencies have installed HFST, the KYTC was one of the first organizations in the United States to establish a formal HFST program–a program considered to be one of the best in the country. The KYTC program was developed in the mid- to late-2000s. One reason for the success of the Kentucky program is the effectiveness of the data analysis processes the State uses in identifying areas where HFST application will maximize the benefit. This benefit has been validated or confirmed through the use of a crash monitoring program prior to and after HFST installation.

1.4 Purpose of the Document

The Federal Highway Administration (FHWA) works with States to accelerate the use of innovative technologies and programs, especially those where the proof of the concept has been validated with field data, under the Every Day Counts 2 Program.3 In 2012 under this program, HFST was selected as one of the safety initiatives. FHWA aims to mainstream HFST as a safety countermeasure on the Nation's highway to decrease serious injuries and fatalities. This document is a case study on the Kentucky HFST program from inception to full-scale deployment.

The FHWA partnered with the American Traffic Safety Service Association, Inc. (ATSSA) and the American Association of State Highway and Transportation Officials (AASHTO) to develop material and performance standards to help State departments of transportation (DOT) and local transportation agencies to implement and use HFST. The standard was published in 2014 as PP79, High Friction Surface Treatment for Asphalt and Concrete Pavements. This case study on the Kentucky HFST program was prepared as part of this assistance and documentation so that other agencies interested in deploying their own programs can benefit from the insights garnered from Kentucky's experiences.

This document summarizes Kentucky's efforts to set up and establish a HFST program for reducing roadway crashes and fatalities and outlines Kentucky's standards, guidance, and specifications for using this safety treatment strategy as a practice for reducing roadway departure crashes in critical areas of the roadway. It also identifies and discusses various elements to consider when selecting roadway segments that are candidates for HFST applications and lists some of the important insights and lessons learned from the Kentucky program. The case study document also includes experiences and lessons learned from HFST installation.

1.5 Scope of the Document

The information for this case study document is based on experiences obtained from Kentucky's formal program to identify and select roadway segments that would be expected to improve roadway departure safety by increasing the available pavement surface friction. Including this Introduction, this case study is organized into seven sections:

  • Section two presents a brief overview on the history of HFSTs, including the successful application of HFSTs made throughout the United States and other areas of the world to address crash issues. It also summarizes the main reasons why Kentucky selected HFST.
  • Section three presents an overview of the development and deployment of Kentucky's HFST program as an element of its overall Strategic Highway Safety Plan. This section also addresses the level of effort and budget needed to deploy this program.
  • Section four focuses on Kentucky's site selection process to maximize the benefit of applying HFSTs.
  • Section five focuses on Kentucky's data analysis in support of selecting high-potential locations that were most likely to see the greatest benefit from using HFST to reduce roadway departure crashes and single and multi-vehicle collisions at intersections.
  • Section six includes information on materials and construction practices used in Kentucky for placing HFSTs and how changes were made in contracting and construction based on the lessons learned from the early years deploying this technology. This section also addresses Kentucky's post construction assessment friction testing methodology.
  • Section seven provides a listing and summary of selected Kentucky HFST projects that document the benefit from using HFST in optimal locations.
  • The final section is the list of references cited throughout the document as well as additional reference material.