As of October 1, 2016, the SWUTC concluded its 28 years of operation and is no longer an active center of the Texas A&M Transportation Institute. The archived SWUTC website remains available here.


SWUTC Research Project Description

Surface Treatments to Alleviate Crashes on Horizontal Curves

University: Texas A&M University

Principal Investigator:
Mike Pratt
Texas Transportation Institute
(979) 845-1907

Funding Source: SPR Program

Total Project Cost: $221,354

Project Number: 0-6714

Date Started: 9/1/12

Estimated Completion Date: 8/31/13

Project Summary

Project Abstract:
The primary objective of this project is to improve safety for motorists through the identification of appropriate usage of surface treatments at horizontal curves. Researchers believe that the application of such treatments at appropriate horizontal curve locations throughout the state will result in better driver performance and thereby reduce the number of crashes experienced at horizontal curves.  The project will contain tasks that:

  • Identify the current state-of-the-practice with regard to high-friction surface treatments;
  • A crash analysis of horizontal curve characteristics factoring into run-off-the-road crashes;
  • Evaluation of current high-friction surface treatments available; and
  • Field studies of surface treatment installations at horizontal curves.

Project Objectives:
Specifically, the objectives of this research are to:

  • determine contributing factors to run-off-the-road (ROT) (roadway departure) crashes at horizontal curves,
  • identify appropriate surface treatments to alleviate crashes,
  • conduct field analysis to determine operational benefits of surface treatments, and
  • develop guidance regarding the application of surface treatments and other traffic control devices at horizontal curves.

Task Descriptions:

Task 1:  State-of-the-Practice Synthesis;

Task 2:  Crash Data Analysis;

Task 3:  Site and Treatment Selection;

Task 4:  Field Evaluation of Surface Treatments;

Task 5:  Prepare Guidelines; and

Task 6:  Prepare Reports.

Implementation of Research Outcomes:
An analysis framework was developed by this research to assess the need for surface treatments at curves based on the concept of margin-of-safety analysis. Models were developed to predict vehicle speeds throughout a curve, and calibrated using data from Texas curve sites. Safety prediction models were also developed to quantify the relationship between skid number and curve crash frequency. This information was assembled to develop guidelines that can be applied to assess the need and potential benefit of installing a high-friction surface treatment on a rural highway horizontal curve. The guidelines are formulated as an Excel®-based spreadsheet program called the Texas Curve Margin of Safety (TCMS). The TCMS program accepts curve geometric and traffic control characteristics as inputs, and provides information about margin of safety, expected crash frequency, and travel path distribution as outputs. The spreadsheet tool is envisioned to be incorporated into the Texas Department of Transportation’s pavement design guidance.

Impacts/Benefits of Implementation:
Practitioners interested in considering a high-friction surface treatment for a horizontal curve should conduct a margin-of-safety analysis to estimate the potential benefit of the treatment. The analysis framework developed in the research project can be implemented to determine the improvement in margin of safety that would result from the installation of a high-friction surface treatment, as well as the expected reduction in crash frequency. The practitioner must obtain data to describe the curve’s geometric characteristics as well as the existing skid number and the expected improvement in skid number following the installation of the surface treatment.

Web Links:
Final Technical Report