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Publication Number: FHWA-RD-98-133
Date: October 1998

Accident Models for Two-Lane Rural Roads: Segment and Intersections

FOREWORD

This report is a direct step for the implementation of the Accident Analysis Module in the Interactive Highway Safety Design Model (IHSDM). The Accident Analysis Module is expected to estimate the safety of two-lane rural highway characteristics for existing and new projects. Several accident models are developed to estimate accident frequencies. The three main models are for road segments (with non-intersection accidents), one-way stop-controlled intersections with three legs, and two-way stop-controlled intersections with four legs. This report describes the collection, analysis, and modeling of accidents on rural roads in Minnesota (1985-1989) and Washington State (1993-1995).

Models of the Poisson type, negative binomial type, and extended negative binomial type are developed, and advanced statistical techniques are applied to assess the explanatory value of the models in the presence of Poisson randomness and overdispersion. The models derived from these data indicate that exposure and traffic counts are the chief highway variables contributing to accidents. Other variables that affect accidents on road segments are: lane width, shoulder width, horizontal and vertical alignments, roadside conditions, and driveway density. Other variables that affect accidents at intersections are: vertical and horizontal alignments, roadside conditions, number of driveways, posted speed, approach angles, and turning lanes.

 

A. George Ostensen, Director

Office of Safety and Traffic

Operations 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.

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.

 

Technical Report Documentation Page

1. Report No.

FHWA-RD-98-133

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

ACCIDENT MODELS FOR TWO-LANE RURAL ROADS: SEGMENTS AND INTERSECTIONS

5. Report Date

October 1998

6. Performing Organization Code
7. Author(s)

Andrew Vogt and Joe G. Bared

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

 

10. Work Unit No. (TRAIS)

3A5A

11. Contract or Grant No.

DTFH61-94-Z-00124

12. Sponsoring Agency Name and Address

Office of Safety and Traffic Operations R&D

Federal Highway Administration

6300 Georgetown Pike

McLean, Virginia 22101-2296

13. Type of Report and Period Covered

Final Report

August 1994 - September 1997

14. Sponsoring Agency Code

 

15. Supplementary Notes

Contracting Officers Technical Representative (COTR): Joe G. Bared, HSR-20

16. Abstract

This report describes the collection, analysis, and modeling of accident and roadway data pertaining to segments and intersections on rural roads in the States of Minnesota (1985-1989) and Washington (1993-1995). The segments are on two-lane roads, and the intersections are three-legged and four-legged intersections of such roads, stop-controlled on the minor legs. Data were acquired from the Highway Safety Information System, photologs, construction plans, and State data bases. More than 1,300 segments and more than 700 intersections are included in the final samples on which the modeling is based. Variables collected include accident counts, traffic exposure, surface and shoulder width, Roadside Hazard Rating, number of driveways, channelization, horizontal and vertical alignments, intersection angles, speed limits, and commercial traffic percentage.

Models of Poisson type, negative binomial type, and extended negative binomial type (the latter due to Shaw-Pin Miaou) are developed, and advanced statistical techniques are applied to assess the explanatory value of the models in the presence of Poisson randomness and overdispersion.

The models derived from these data indicate that exposure and traffic counts are the chief highway variables contributing to accidents, but that surface and shoulder width, roadside conditions, and alignments are also significant, especially in the segment models. Unexpected behavior of intersection angle, Roadside Hazard Rating, number of driveways, and channelization in the intersection models is worthy of note. Despite the incompleteness of the data and uncertainties in the values of some variables, the quantity, quality, and variety of the data give the models both descriptive and predictive value.

17. Key Words

Highway safety, Accident prediction models, Negative binomial regression, Extended negative binomial models, Highway geometric design

18. Distribution Statement

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

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

179

22. Price

Form DOT F 1700.7 Reproduction of completed page authorized

 

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