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Publication Number:  FHWA-HRT-13-077    Date:  January 2014
Publication Number: FHWA-HRT-13-077
Date: January 2014

 

Safety Effects of Horizontal Curve and Grade Combinations on Rural Two-Lane Highways

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Location Corrected Values URL
Page i, Block 21 68 /publications/research/safety/13077/index.cfm#errata01
Page 4, SAFETY EFFECTS OF HORIZONTAL ALIGNMENT, Paragraph 1, Sentence 1, Line 2 shown in figure 2 /publications/research/safety/13077/002.cfm#errata02
Page 4, SAFETY EFFECTS OF HORIZONTAL ALIGNMENT, Paragraph 1, Sentence 1, Figure 2 N = [1.55 (LC)(V) + 0.014(D)(V) − 0.012(S)(V)](0.978)W − 30 /publications/research/safety/13077/002.cfm#errata03
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Page 8, Paragraph 1, Sentence 10 [A = abs(G1 – G2 )] /publications/research/safety/13077/003.cfm#errata06
Page 9, DESCRIPTIVE STATISTICS, Paragraph 1, Sentence 1 [million vehicle miles traveled in the 6-year period (MVMT)] /publications/research/safety/13077/003.cfm#errata07
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Page 17, Horizontal Curves and Tangents on Straight Grades, Paragraph 1,Sentence 1, Bullet 1 [number of roadway segments (N) = 8,095 and total roadway length = 595 mi] /publications/research/safety/13077/004.cfm#errata11
Page 17, Horizontal Curves and Tangents on Straight Grades, Paragraph1, Sentence 1 (i.e., number of roadway sections; total roadway length; and minimum, maximum, mean, and median values for specific parameters) /publications/research/safety/13077/004.cfm#errata12
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Report - FHWA-HRT-13-077 Summary Report - FHWA-HRT-13-078 Excel Calcuator Tool - HRTM 2130

 

FOREWORD

The first edition of the American Association of State Highway and Transportation Officials (AASHTO) Highway Safety Manual (HSM) provides crash modification factors (CMFs) for the safety effects of horizontal curvature and percent grade on rural two-lane highways.(1) However, the HSM does not provide a method to account for the interactions between these effects. Researchers have always presumed that there are interactions between the safety effects of horizontal and vertical alignment, but this has not been demonstrated for specific alignment combinations in a form useful for safety prediction.

This document is a final report highlighting research undertaken to quantify the safety effects of five specific combinations of horizontal and vertical alignment for rural two-lane highways. The research is based on data from the Federal Highway Administration’s Highway Safety Information System (HSIS) for Washington State, including roadway characteristics, horizontal and vertical alignment, traffic volume, and crashes. The outcome is a set of safety prediction models for fatal and injury and property damage only crashes. CMFs representing safety performance relative to level tangents on rural two-lane highways were developed from the models for each of the five combinations of horizontal and vertical alignment to present the results in a form suitable for incorporation in the HSM. This report should be of interest to safety engineers and planners as well as other AASHTO HSM users.

Monique R. Evans
Director, Office of Safety
Research and Development

 

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.

 

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

Technical Report Documentation Page

1. Report No.

FHWA-HRT-13-077

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

Safety Effects of Horizontal Curve and Grade Combinations on Rural Two- Lane Highways

5. Report Date

January 2014

6. Performing Organization Code
7. Author(s)

Karin M. Bauer and Douglas W. Harwood

8. Performing Organization Report No.

110785.01.001

9. Performing Organization Name and Address

MRIGlobal
425 Volker Blvd
Kansas City, MO 64110

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-11-C-00050

12. Sponsoring Agency Name and Address

Federal Highway Administration Office of Safety Research and Development 6300 Georgetown Pike McLean, VA 22101-2296

13. Type of Report and Period Covered

Final Report December 2010–August 2012

14. Sponsoring Agency Code

 

15. Supplementary Notes

This work was performed under subcontract with the University of North Carolina (UNC) Highway Safety Research Center for Highway Safety Information System (HSIS) under Master Agreement No. 5-555697 Contract No. DTFH61 06 C 000013 and under subcontract for HSIS under Master Agreement No. 5-55771 Contract No. DTFH61 11 C 00050. The UNC Program Manager was David L. Harkey, and the Federal Highway Administration HSIS Program Manager was Carol Tan, Ph.D.

16. Abstract

This report summarizes the results of research undertaken to quantify the safety effects of five types of horizontal and vertical alignment combinations for rural two-lane highways. The research is based on Federal Highway Administration Highway Safety Information System data for Washington State, including crash records from 2003 to 2008. The outcome is a set of safety prediction models for fatal and injury and property damage only crashes.

 

To present the results in a form suitable for incorporation in the American Association of State Highway and Transportation Officials Highway Safety Manual, crash modification factors representing safety performance relative to level tangents were developed from these models for each of the five combinations of horizontal and vertical alignment—horizontal curves and tangents on straight grades, horizontal curves and tangents at type 1 crest vertical curves, horizontal curves and tangents at type 1 sag vertical curves, horizontal curves and tangents at type 2 crest vertical curves, and horizontal curves and tangents at type 2 sag vertical curves.(1)

17. Key Words

Safety, Horizontal curves, Vertical curves, Grade interaction, Crests, Sags, Rural two-lane highways, Crash modeling, Safety performance function, Crash modification factor

18. Distribution Statement

No restrictions. This document is available to the public through the National Technical Information Service, Springfield, VA 22161

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

63 68*

22. Price

N/A

Form DOT F 1700.7 Reproduction of completed page authorized

*Modified on November 16, 2014

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

CHAPTER 1—INTRODUCTION

CHAPTER 2—STATE OF KNOWLEDGE LITERATURE REVIEW

CHAPTER 3—DATABASE DESCRIPTION

CHAPTER 4—STATISTICAL ANALYSIS

CHAPTER 5—CRASH MODIFICATION FACTORS

CHAPTER 6—CONCLUSIONS AND RECOMMENDATIONS

REFERENCES

LIST OF FIGURES

LIST OF TABLES

 

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