Preliminary Scope

FHWA Technical Advisory T5040 provides information and guidelines for implementing a pavement friction management program (PFMP), which helps state DOTs refine their friction testing practices and places a greater emphasis on the relationship between crashes and pavement friction to minimize friction-related crashes. In the case of macrotexture, NCHRP Report 964 describes the protocols for network-level macrotexture measurements. However, one of the key components of any PFMP is the network safety analysis. For such an analysis, a functional relationship between crashes (or crash risks) and skid resistance is needed, i.e., a safety performance function (SPF) that uses friction and/or texture as one of the safety predictors. To develop SPFs, agencies may use different crash and safety performance metrics (e.g., a wet/dry crash ratio, wet crash frequencies, the type and severity of the crash, etc.) as well as specifying different time windows over which to analyze the crashes. Moreover, depending on the crash reports and the structure of the database, the crash metric used may correspond to one or two traffic directions. Finally, the model structure defined for the SPF can differ among DOTs: some utilize the negative binomial model framework described in the Highway Safety Manual (HSM), while others include model coefficients to represent a panel data structure, random effects, spatial correlations, clustering analysis, machine learning, etc.

Because of this great variation in defining these components for safety analysis, there is a need to document the different methods and practices used by state DOTs to model safety performance as a function of skid resistance and to integrate this analysis into a comprehensive PFMP.

The objective of this synthesis is to document current and anticipated state DOT practices and methods to (1) measure pavement friction and texture; (2) account for friction and texture during associated design processes (e.g., mixture, geometrical, etc.); (3) model the relationship between these parameters and highway safety; and (4) integrate this information into pavement management processes. 

Information to be gathered includes (but is not limited to):

• Testing technologies, measurement protocols, and analysis techniques used to characterize skid resistance (friction and texture). These include (1) performance models; (2) possible correction factors (e.g., testing speeds, temperature, seasonality, etc.); (3) measurement frequency; (4) testing location; (5) delineation of homogeneous sections; and (6) representative index value to correlate with safety and to represent pavement performance.
• Identify whether friction and/or texture demand are accounted for during the roadway and materials design processes.
• Identify analysis tools used by each state DOT to model safety performance, including identifying the variables frequently used as safety descriptors, whether skid resistance is considered as a safety descriptor, and if that is the case, what is the safety metric used.
• Identify the factors used to define friction demand categories. 
• Identify the extent to which DOTs are integrating their PFMP into the broader pavement management system, including prioritization and optimization.
• What data collection plans do the DOTs use? How frequently is data collected?
• How often is the model updated?

Information will be gathered through a literature review, a survey of state DOTs, and follow-up interviews with selected DOTs for the development of case examples. Information gaps and suggestions for research to address those gaps will be identified.

Information Sources (Partial)

• Flintsch, G.W., et al. (2021). NCHRP Report 964: Protocols for Network-Level Macrotexture Measurement. National Academies of Sciences, Engineering, and Medicine. Washington, DC: The National Academies Press. https://doi.org/10.17226/26225.
• Guide for Pavement Friction, 2^nd Edition, 2022.
• Highway Safety Manual, 1^st Edition, 2010.
• FHWA Technical Advisory T 5040.38: Pavement Friction Management Program.
• FHWA-RC-20-0009 PFM Program Utilizing Continuous Friction Measurement Equipment and State-of-the-Practice Safety Analysis Demonstration.
• NCHRP Synthesis 20-05/Topic 54-10: State Customization of Highway Safety Manual Methods.

TRB Staff
Sandra Q. Larson
Email: slarson@nas.edu

Meeting Dates
First Panel Meeting: TBD
Teleconference with Consultant: TBD
Second Panel Meeting: TBD