U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000


Skip to content U.S. Department of Transportation/Federal Highway AdministrationU.S. Department of Transportation/Federal Highway Administration

Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations

 
Report
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number: FHWA-RD-97-106

Rural Public Transportation Technologies: User Needs and Applications FR1-798

U.S. DOT FHWA

Turner-Fairbanks Highway Research Center

Technical Report Documentation Page

Go to the Table of Contents

1. Report No.

FHWA-RD-97-106

2. Government Accession No.

 

3. Recipient's Catalog No.

 

4. Title and Subtitle

STATISTICAL MODELS OF ACCIDENTS ON INTERCHANGE RAMPS AND SPEED-CHANGE LANES

5. Report Date

6. Performing Organization

7. Author(s)

K.M. Bauer and D.W. Harwood

8. Performing Organization Report No.

3195-02

9. Performing Organization Name and Address

Midwest Research Institute
425 Volker Boulevard
Kansas City, Missouri 64110-2299

10. Work Unit No. (TRAIS)

3A5A

11. Contract or Grant No.

DTFH61-92-C-00031

12. Sponsoring Agency Name and Address

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

13. Type of Report and Period Covered

Final Technical Report
May 1994 - July 1997

14. Sponsoring Agency Code

15. Supplementary Notes

Contracting Officer's Technical Representative (COTR): Joe Bared, HSR-20

 

16. Abstract

The objective of this research was to develop statistical models for defining the relationship between traffic accidents and highway geometric design elements and traffic volumes for interchange ramps and speed-change lanes. The data base used to develop the models consisted of data for interchange ramps and speed-change lanes in the State of Washington and was obtained from the FHWA Highway Safety Information System. Additional geometric design features were obtained from the review of interchange diagrams. Data on other geometric design features, such as the ramp grades and horizontal curvature, were collected for a sample of ramps from aerial photographs and other existing highway agency files.

The statistical modeling approaches used in the research included Poisson and negative binomial regression. Regression models to determine relationships between accidents and the geometric design and traffic volume characteristics of ramps were difficult to develop because the observed accident frequencies for most ramps and speed-change lanes are very low. The regression models developed, based on the negative binomial distribution, explained between 10 and 42 percent of the variability in the accident data, with the negative binomial distribution providing a poor to moderate fit to the data. However, most of that variability was explained by ramp Annual Average Daily Traffic (AADT). Other variables found to be significant in some models included mainline freeway AADT, area type (rural/urban), ramp type (on/off), ramp configuration, and combined length of ramp and speed-change lane.

The best models obtained for predicting accident frequencies were those obtained when modeling the combined accident frequency for an entire ramp, together with its adjacent speed-change lanes. These models provided a better fit than separate models for ramps and speed-change lanes. Models developed to predict total accidents generally performed slightly better than did models to predict fatal and injury accidents.

17. Key Words

Accident Modeling Poisson Regression
Traffic Accidents Negative Binomial
Geometric Design Regression
Interchange Ramps Speed-Change Lanes

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

163

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized


TABLE OF CONTENTS

CHAPTER 1:

INTRODUCTION

CHAPTER 3:

DATA BASE SELECTION

REFERENCES


LIST OF FIGURES
  1. Typical Interchange Configurations
  2. Typical Ramp Configurations
  3. Illustration of Ramps and Adjacent Speed-Change Lanes
  4. Typical Interchange Diagram Used to Determine Relationships Between Interchange Elements
  5. Accident Frequency Distributions for Entire Ramps
  6. Accident Frequency Distributions for Ramp Proper Segments: Off-Ramps vs. On-Ramps
  7. Total Accident Frequency Distributions for Ramp Proper Segments: Off-Ramps vs. On-Ramps
  8. Fatal and Injury Accident Frequency Distributions for Ramp Proper Segments: Off-Ramp vs On-Ramp
  9. Accident Frequency Distribution for Ramp Proper Segments, Off-Ramps Only (Rear-end Accidents Excluded
  10. Accident Frequency Distribution for Entire Ramps, Off-Ramps Only (Rear-End Accidents Excluded)
  11. Accident Frequency Distributions for Speed-Change Lanes
  12. Accident Frequency Distributions for Entire Ramps, Including the Adjacent Speed-Change Lane
  13. Accident Frequency Distributions for Urban Diamond Off-Ramps
  14. Accident Frequency Distributions for Urban Parclo and Free-Flow Loop Off-Ramps
  15. Accident Frequency Distributions for Urban Outer Connection Off-Ramps
  16. Annual Accident Frequency Distributions for Entire Ramps (1993-1995)
  17. Annual Accident Frequency Distributions for Ramp Proper Segments (1993-1995)
List of Tables
  1. Accident Rates on Outer Connection Ramps as a Function of Curvature and Average Daily Traffic Volume
  2. Accident Rates for Loop Ramps as a Function of Curvature and Average Daily Traffic Volume
  3. Accident Rates by Ramp Type and Configuration
  4. Accident Rates by Area Type and Interchange Unit
  5. Variables Available in the Existing Washington Data Base for Ramps and Speed-Change Lanes
  6. Accident History Variables Derived From Washington State Accident File
  7. Additional Variables Obtained From Review of Data and Interchange Diagrams
  8. Additional Variables Obtained From Review of Other Highway Agency Records
  9. Number of Ramps by Facility Type, Ramp Type, and Area Type
  10. Number of Interstate Ramps by Ramp Configuration, Area Type, and Ramp Type
  11. Number of Entire Ramps by Ramp Configuration, Area Type, and Ramp Type
  12. Number of Ramp Proper Segments by Ramp Configuration, Area Type, and Ramp Type
  13. Total Accident Frequencies and Rates for Entire Ramps by Ramp Configuration, Area Type, and Ramp Type (1993-1995)
  14. Fatal and Injury Accident Frequencies and Rates for Entire Ramps by Ramp Configuration, Area Type, and Ramp Type (1993-1995)
  15. Descriptive Statistics for Ramp Proper Segments
  16. Model Diagnostics for Total and Fatal and Injury Accidents on Ramp Proper Segments
  17. Negative Binomial Regression Results for Total Accident on Ramp Proper Segments
  18. Negative Binomial Regression Results for Fatal and Injury Accidents on Ramp Proper Segments
  19. Descriptive Statistics for Ramp Proper Segments on Off-Ramps (Rear-End Accidents Excluded)
  20. Model Diagnostics for Total and Fatal and Injury Accidents for Ramp Proper Segments of Off-Ramps (Rear-End Accidents Excluded)
  21. Negative Binomial Regression Results for Total Accidents for Ramp Proper Segments on Off-Ramps (Rear-End Accidents Excluded)
  22. Negative Binomial Regression Results for Fatal and Injury Accidents for Ramp Proper Segments on Off-Ramps (Rear-End Accidents Excluded)
  23. Descriptive Statistics for Entire Ramps
  24. Model Diagnostics for Total and Fatal and Injury Accidents on Entire Ramps
  25. Negative Binomial Regression Results for Total Accidents on Entire Ramps
  26. Negative Binomial Regression Results for Fatal and Injury Accidents on Entire Ramps
  27. Descriptive Statistics for Entire Off-Ramps (Rear-End Accidents Excluded)
  28. Model Diagnostics for Total and Fatal and Injury Accidents on Enter Off-Ramps (Rear-End Accidents Excluded)
  29. Negative Binomial Regression Results for Total and Fatal and Injury Accidents on Entire Off-Ramps (Rear-End Accidents Excluded)
  30. Descriptive Statistics for Speed-Change Lanes
  31. Model Diagnostics for Total and Fatal and Injury Accidents in Speed-Change Lanes
  32. Negative Binomial Regression Results for Total Accidents in Acceleration Lanes (Diamond On-Ramps Only)
  33. Negative Binomial Regression Results for Fatal and Injury Accidents in Acceleration Lanes (Diamond On-Ramps Only)
  34. Descriptive Statistics for Entire Ramps, Including the Adjacent Speed-Change Lane
  35. Model Diagnostics for Total and Fatal and Injury Accidents on Entire Ramps, Including the Adjacent Speed-Change Lane
  36. Negative Binomial Regression Results for Total Accidents on Entire Ramps, Including the Adjacent Speed-Change Lane (Reduced Model at 10-Percent Significance Level)
  37. Negative Binomial Regression Results for Fatal and Injury Accidents on Entire Ramps, Including the Adjacent Speed-Change Lane (Reduced Model at 10-Percent Significance Level)
  38. Negative Binomial Regression Results for Total Accidents on Entire Ramps, Including the Adjacent Speed-Change Lane (Reduced Model at 20-Percent Significance Level)
  39. Negative Binomial Regression Results for Fatal and Injury Accidents on Entire Ramps, Including the Adjacent Speed-Change Lane (Reduced Model at 20-Percent Significance Level)
  40. Descriptive Statistics for Urban Diamond Off-Ramps
  41. Model Diagnostics for Total and Fatal and Injury Accidents on Urban Diamond Off-Ramps
  42. Summary of Statistically Significant Variables in Modeling Accidents on Urban Diamond Off-Ramps
  43. Expected Accident Experience for Rural Off-Ramps
  44. Expected Accident Experience for Rural On-Ramps
  45. Expected Accident Experience for Urban Off-Ramps
  46. Expected Accident Experience for Urban On-Ramps
  47. Definitions of Variable Considered in Statistical Modeling Of Ramp and Speed-Change Lane Accidents
  48. Accident Severity Distribution by Ramp Segment Type for Rural Diamond Off-Ramps (1993 Through 1995)
  49. Accident Severity Distribution by Ramp Segment Type for Rural Diamond On-Ramps (1993 Through 1995)
  50. Accident Severity Distribution by Ramp Segment Type for Urban Diamond Off-Ramps (1993 Through 1995)
  51. Accident Severity Distribution by Ramp Segment Type for Urban Parclo Loop Off-Ramps (1993 Through 1995)
  52. Accident Severity Distribution by Ramp Segment Type for Urban Free-Flow Off-Ramps (1993 Through 1995)
  53. Accident Severity Distribution by Ramp Segment Type for Urban Outer Connection Off-Ramps (1993 Through 1995)
  54. Accident Severity Distribution by Ramp Segment Type for Urban Direct and Semi-Direct Connection Off-Ramps (1993 Through 1995)
  55. Accident Severity Distribution by Ramp Segment Type for Urban C/D Roads (1993 Through 1995)
  56. Accident Type Distribution by Ramp Segment Type for Rural Diamond Off-Ramps (1993 Through 1995)
  57. Accident Type Distribution by Ramp Segment Type for Rural Diamond On-Ramps (1993 Through 1995)
  58. Accident Type Distribution by Ramp Segment Type for Urban Urban Diamond Off-Ramps (1993 Through 1995)
  59. Accident Type Distribution by Ramp Segment Type for Urban Parclo Loop Off-Ramps(1993 Through 1995)
  60. Accident Type Distribution by Ramp Segment Type for Urban Free-Flow Loop Off-Ramps (1993 Through 1995)
  61. Accident Type Distribution by Ramp Segment Type for Urban Outer Connection Off-Ramps (1993 Through 1995)
  62. Accident Type Distribution by Ramp Segment Type for Urban Direct and Semi-Direct Connection Ramps (1993 Through 1995)
  63. Accident Type Distribution by Ramp Segment Type for Urban C/D Roads(1993 Through 1995)
ResearchFHWA
FHWA
United States Department of Transportation - Federal Highway Administration