Technical Report Documentation Page
1. Report No.
2. Government Accession No.
3. Recipient's Catalog No.
FHWA/TX-07/0-5439-P1
4. Title and Subtitle
5. Report Date
HORIZONTAL CURVE SIGNING HANDBOOK
August 2007
Published: October 2007
6. Performing Organization Code
7. Author(s)
8. Performing Organization Report No.
J. Bonneson, M. Pratt, J. Miles, and P. Carlson
Product 0-5439-P1
9. Performing Organization Name and Address
10. Work Unit No. (TRAIS)
Texas Transportation Institute
The Texas A&M University System
11. Contract or Grant No.
College Station, Texas 77843-3135
Project 0-5439
12. Sponsoring Agency Name and Address
13. Type of Report and Period Covered
Texas Department of Transportation
Product
Research and Technology Implementation Office
P.O. Box 5080
14. Sponsoring Agency Code
Austin, Texas 78763-5080
15. Supplementary Notes
Project performed in cooperation with the Texas Department of Transportation and the Federal Highway
Administration.
Project Title: Identifying and Testing Effective Advisory Speed Setting Procedures
URL: http://tti.tamu.edu/documents/0-5439-P1.pdf
16. Abstract
Horizontal curves are a necessary component of the highway alignment; however, they tend to be associated
with a disproportionate number of severe crashes. Warning signs are intended to improve curve safety by
alerting the driver of a change in geometry that may not be apparent or expected. However, several research
projects conducted in the last 20 years have consistently shown that drivers are not responding to curve
warning signs nor complying with the Advisory Speed plaque.
The procedures described in this handbook are intended to improve consistency in curve signing and driver
compliance with the advisory speed. The handbook describes guidelines for determining when an advisory
speed is needed, criteria for identifying the appropriate advisory speed, an engineering study method for
determining the advisory speed, and guidelines for selecting other curve-related traffic control devices.
The handbook is intended for use by traffic engineers and technicians that have been given the responsible
charge of evaluating and maintaining horizontal curve signing and delineation devices. The procedures
described in this handbook are applicable to rural highways. However, they may be useful for establishing
advisory speeds for urban streets.
17. Key Words
18. Distribution Statement
Traffic Control Devices, Warning Signs, Speed
No restrictions. This document is available to the
Signs, Highway Curves, Speed Measurement,
public through NTIS:
Trucks, Traffic Speed
National Technical Information Service
Springfield, Virginia 22161
http://www.ntis.gov
19. Security Classif.(of this report)
20. Security Classif.(of this page)
21. No. of Pages
22. Price
Unclassified
Unclassified
56
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

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HORIZONTAL CURVE SIGNING HANDBOOK
by
J. Bonneson, P.E.
Senior Research Engineer
Texas Transportation Institute
M. Pratt
Associate Transportation Researcher
Texas A&M University
J. Miles
Associate Transportation Researcher
Texas Transportation Institute
and
P. Carlson, P.E.
Associate Research Engineer
Texas Transportation Institute
Product 0-5439-P1
Project 0-5439
Project Title: Identifying and Testing Effective Advisory Speed Setting Procedures
Performed in cooperation with the
Texas Department of Transportation
and the
Federal Highway Administration
August 2007
Published: October 2007
TEXAS TRANSPORTATION INSTITUTE
The Texas A&M University System
College Station, Texas 77843-3135

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DISCLAIMER
The contents of this handbook reflect the views of the authors, who are responsible for the
facts and the accuracy of the data published herein. The contents do not necessarily reflect the
official view or policies of the Federal Highway Administration (FHWA) and/or the Texas
Department of Transportation (TxDOT). This handbook does not constitute a standard,
specification, or regulation. It is not intended for construction, bidding, or permit purposes. The
engineer in charge of the project was James Bonneson, P.E. #67178.
NOTICE
The United States Government and the State of Texas do not endorse products or
manufacturers. Trade or manufacturers’ names appear herein solely because they are considered
essential to the object of this handbook.
v

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ACKNOWLEDGMENTS
The research project that led to the development of this handbook was sponsored by the
Texas Department of Transportation and the Federal Highway Administration. The research was
conducted by Dr. James Bonneson, Mr. Michael Pratt, Mr. Jeff Miles, and Dr. Paul Carlson. These
researchers are employees with the Texas Transportation Institute (TTI).
The researchers would like to acknowledge the support and guidance provided by the Project
Monitoring Committee:
! Mr. Paul Frerich, Project Coordinator;
! Ms. Marla Jasek, Project Director;
! Mr. James Bailey;
! Mr. Herbert Bickley;
! Mr. Carlos Ibarra; and
! Mr. Darren McDaniel.
All of the committee members are employees with TxDOT. In addition, the researchers would like
to acknowledge the valuable assistance provided by Mr. Todd Hausman (with TTI) during the data
collection and reduction phase of the project. The effort of these individuals is greatly appreciated.
vi

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TABLE OF CONTENTS
Page
LIST OF FIGURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
CHAPTER 1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
PURPOSE AND SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
CHAPTER 2. COMMUNICATING CHANGES IN HORIZONTAL ALIGNMENT . . . . 3
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
HORIZONTAL CURVE SAFETY AND OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
WARNING SIGNS FOR CHANGES IN HORIZONTAL ALIGNMENT . . . . . . . . . . . . . . . . . . 5
TEXAS CURVE ADVISORY SPEED SOFTWARE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
CHAPTER 3. PROCEDURE FOR ESTABLISHING ADVISORY SPEED . . . . . . . . . . . 11
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
DIRECT METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
COMPASS METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
CHAPTER 4. CURVE SIGNING GUIDELINES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
OVERVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
GUIDELINES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
APPENDIX A. ADVISORY SPEED CRITERIA AND ISSUES . . . . . . . . . . . . . . . . . . . . . 27
APPENDIX B. SELECTED TABLES FROM THE TMUTCD . . . . . . . . . . . . . . . . . . . . . . 39
APPENDIX C. DATA COLLECTION SHEET . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
vii

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LIST OF FIGURES
Figure
Page
1
Effect of Radius, Tangent Speed, and Vehicle Type on Curve Speed . . . . . . . . . . . . . . . . . 4
2
Curve Crash Rate as a Function of Radius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3
Curve Warning Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4
TCAS Welcome Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5
TCAS Analysis Worksheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6
Location of Critical Portion of Curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7
Camcorder View of Measuring Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8
TCAS Input Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9
TCAS Advisory Speed Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
10
Effect of Lateral Shift on Travel Path Radius . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
11
Guidelines for the Selection of Curve-Related Traffic Control Devices . . . . . . . . . . . . . . 22
12
TCAS Traffic Control Device Guidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
A-1 Relationship between Curve Speed, Ball-Bank Reading, and Radius . . . . . . . . . . . . . . . . 31
A-2 Ball-Bank Readings from Two Test Runs with Different Technicians . . . . . . . . . . . . . . . 32
A-3 Comparison of Posted and Estimated Advisory Speeds . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
A-4 Relationship between Radius, Speed, and Ball-Bank Reading . . . . . . . . . . . . . . . . . . . . . 35
A-5 Comparison of the 50th Percentile Curve Speed with the Advisory Speed . . . . . . . . . . . . 36
A-6 Relationship between Speed Limit and 85th Percentile Speed . . . . . . . . . . . . . . . . . . . . . . 37
viii

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LIST OF TABLES
Table
Page
1
Guidelines for the Selection of Curve-Related Traffic Control Devices . . . . . . . . . . . . . . 23
B-1 Guidelines for Advance Placement of Warning Signs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
B-2 Horizontal Alignment Sign Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
B-3 Delineator and Chevron Sign Spacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
ix

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Document Outline

• Technical Report Documentation Page
• Author's Title Page
• Disclaimer
• Notice
• Acknowledgments
• Table of Contents
• List of Figures
• List of Tables
• Chapter 1. Introduction
  • Overview
  • Purpose and Scope
• Chapter 2. Communicating Changes in Horizontal Alignment
  • Overview
  • Horizontal Curve Safety and Operation
  • Warning Signs for Changes in Horizontal Alignment
  • Texas Curve Advisory Speed Software
• Chapter 3. Procedure for Establishing Advisory Speed
  • Overview
  • Direct Method
  • Compass Method
• Chapter 4. Curve Signing Guidelines
  • Overview
  • Guidelines
• References
• Appendix A. Advisory Speed Criteria and Issues
• Appendix B. Selected Tables from the TMUTCD
• Appendix C. Data Collection Sheet

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