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

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

TABLE OF CONTENTS

1. INTRODUCTION

 

2. LITERATURE REVIEW

SEGMENT MODELS

SEGMENT VARIABLES

Average Daily Traffic (ADT)

Lane Width, Shoulder Width, and Shoulder Type

Horizontal and Vertical Alignment

Roadside and Terrain Condition

Speed

Driveways

INTERSECTION MODELS

INTERSECTION VARIABLES

Traffic Flow

Control Type

Sight Distance and Alignment

ARTIFICIAL NEURAL NETWORKS

 

3. DATA COLLECTION

THE POPULATIONS AND SAMPLE SELECTION

Minnesota Segments

Minnesota Intersections

Washington Segments

Washington Intersections

HOW DATA WERE COLLECTED

HSIS Data

Minnesota Photologs

Minnesota Construction Plans

Washington Videotapes

Weather Data

Miscellaneous Investigations

LIMITATIONS ON DATA QUALITY

Accident Data

Traffic Data

Alignment Data

Location Uncertainties

Time Uncertainties

Miscellaneous Limitations

SUMMARY

 

4. ANALYSIS

NEW VARIABLES

Accident Variables

Traffic Variables

Horizontal Alignment Variables

Vertical Alignment Variables

Angle Variables

Miscellaneous Variables

UNIVARIATE STATISTICS

Minnesota versus Washington

Segments versus Intersections

Minnesota Sample versus Population

BIVARIATE STATISTICS

Segment Accidents

Three-legged Intersection Accidents

Four-legged Intersection Accidents

Other Bivariate Relationships

SUMMARY

 

5. MODELING

POISSON AND NEGATIVE BINOMIAL MODELING TECHNIQUES

The Poisson and Negative Binomial Models

Model Evaluation - Overdispersion

Model Evaluation - Goodness of Fit

SEGMENT MODELS

The State Variable

The Exposure Variable

Lane Width and Shoulder Width

Horizontal and Vertical Curve Variables

Grade, Roadside Hazard Rating, Driveway Density, and Other Variables

Poisson versus Negative Binomial

The Extended Negative Binomial

INTERSECTION MODELS

Traffic

Alignment, Channelization, and Speed

Roadside Variables - Number of Driveways and Hazard Rating

The Angle Variable

Negative Binomial Models - Minnesota versus Washington

Additional Negative Binomial Runs

Negative Binomial Models for Injury Accidents

Final Intersection Models

LOGISTIC MODELING

Theory

Results

SUMMARY

 

6. VALIDATION AND FURTHER ANALYSIS

VALIDATION

Validation Techniques

Minnesota Models versus Later Minnesota Data

Minnesota Models versus Washington Data

Washington and Combined Segment Models versus Minnesota Data

EXPLANATORY VALUE OF FINAL MODELS

CUMULATIVE SCALED RESIDUALS

SUMMARY

 

7. CONCLUSIONS

REFERENCES

APPENDIX 1 - STATISTICS ON THE MINNESOTA POPULATIONS

APPENDIX 2 - FINAL MODELS IN METRIC UNITS

LIST OF FIGURES AND TABLES

INDEX OF VARIABLES

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