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IHSDM Intersection Diagnostic Review Model

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FOREWORD

This report documents the results of the development of an expert system for intersection safety that is part of the Interactive Highway Safety Design Model (IHSDM). The objective was to develop software to perform a diagnostic review of intersections on rural two-lane highways, referred to as the Intersection Diagnostic Review Model (IDRM). This report focuses on documenting the knowledge base developed for the IDRM software. It also documents the software in that it identifies the knowledge structure, problem definitions, models, decision algorithms, formulas, and parameter values implemented in the software.

Technical Report Documentation Page

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

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

1.0 INTRODUCTION

1.1 Role of the Intersection Diagnostic Review Model (IDRM) in the IHSDM

1.2 IDRM Objectives

1.3 The Knowledge Base Development Process

1.4 IDRM as an Expert System

1.5 IDRM Knowledge Base

1.6 Use of IDRM Results

2.0 KNOWLEDGE BASE SCOPE AND APPROACH

2.1 Issues Addressed

2.2 Guiding Principles Used in Knowledge Base Development

2.3 Highway Design Data

2.4 Concerns Identified by IDRM

2.5 Overview of IDRM Models

2.6 Use of IDRM Models to Evaluate Concerns

2.7 Overview of IDRM Treatment Recommendations

3.0 IDRM MODELS

3.1 Intersection Sight Distance for Case B1 – Left Turn From Minor Road

3.2 Intersection Sight Distance for Case B2 – Right Turn From Minor Road

3.3 Intersection Sight Distance for Case B3 – Crossing Maneuver From Minor Road

3.4 Intersection Sight Distance for Case F – Left Turn From Major Road

3.5 Stopping Sight Distance for Vertical Curves

3.6 Stopping Sight Distance for Horizontal Curves

3.7 Visibility Distance to Traffic Signal

3.8 Visibility Distance to Stop Sign

3.9 Visibility Distance to Yield Sign

3.10 Decision Sight Distance for Vertical Curves

3.11 Decision Sight Distance for Horizontal Curves

3.12 Clearance Time for Skewed Intersection

3.13 Left-Turn Lane Warrants

3.14 Right-Turn Lane Warrants

3.15 Left-Turn Lane Length for Closely Spaced Intersections

3.16 Intersection Conflict Index

3.17 Minor-Road Profile

3.18 Intersection Pavement Area

3.19 Change in Approach Alignment Between Opposing Approaches

3.20 Queue Length Prediction

3.21 Horizontal Curve Design for Braking and Cornering

4.0 IDRM CONCERNS

4.1 Insufficient Intersection Sight Distance

4.2 Insufficient Intersection Sight Distance for Intersection on a Horizontal Curve

4.3 Insufficient Intersection Sight Distance for a Horizontal Curve on an Intersection Approach

4.4 Insufficient Intersection Sight Distance for Intersection on Approaches to Crest Vertical Curve

4.5 Insufficient Intersection Sight Distance for Multileg Intersection

4.6 Insufficient Intersection Sight Distance for Intersections With More Than One Minor-Road Approach on the Same Side of the Major Road

4.7 Insufficient Intersection Sight Distance for Skewed Intersections

4.8 Insufficient Stopping Sight Distance for a Crest Vertical Curve on an Intersection Approach

4.9 Insufficient Stopping Sight Distance for a Horizontal Curve on an Intersection Approach

4.10 Insufficient Visibility of Traffic Signal

4.11 Insufficient Visibility of Stop Sign

4.12 Insufficient Visibility of Yield Sign

4.13 Insufficient Decision Sight Distance for a Crest Vertical Curve on an Intersection Approach

4.14 Insufficient Decision Sight Distance for a Horizontal Curve on an Intersection Approach

4.15 Insufficient Decision Sight Distance for Multileg Intersection

4.16 Insufficient Decision Sight Distance for Intersections With More Than One Minor-Road Approach on the Same Side of the Major Road

4.17 Increased Crossing Distance

4.18 Warranted Left-Turn Lane Is Not Present

4.19 Warranted Right-Turn Lane Is Not Present

4.20 Insufficient Left-Turn Bay Storage and Deceleration Length Between Closely Spaced Intersections

4.21 Insufficient Taper Length for Left-Turn Lanes Between Closely Spaced Intersections

4.22 High Traffic Conflict Index

4.23 Uneven, Discontinuous Minor-Road Profile Through Intersection

4.24 Large Intersection Pavement Area

4.25 Approach Alignment Differs Between Opposing Approaches

4.26 Insufficient Queue Storage

4.27 Loss of Control Potential Due to Frequent Braking

5.0 USE OF ACCIDENT HISTORY DATA TO HIGHLIGHT PARTICULAR       INTERSECTION-LEG CONCERNS

5.1 Role of Site-Specific Accident History Data in IDRM

5.2 Conceptual Approach to Use of Site-Specific Accident History Data in IDRM

5.3 Identification of Patterns of Specific Collision Types

5.4 Algorithm for Use in IDRM

5.5 Use of Table 25 to Identify Accident Patterns of Interest

5.6 Summary

6.0 IDRM TREATMENT RECOMMENDATIONS

APPENDIX A – IDRM TREATMENT DETAILS

LIST OF FIGURES

Figure 1. IHSDM Functional Overview

Figure 2. Departure Sight Triangles for ISD Cases B1, B2, and B3

Figure 3. Regions of the Sight Triangle for Which Users Will Be Queried About the Presence of Roadside Sight Obstructions

Figure 4. Visibility Distance to Traffic Signal

Figure 5. Skewed Intersection

Figure 6. Minimum Distance Between Closely Spaced Intersections

Figure 7. Area of Skewed Intersections for Two-Lane Rural Intersections

Figure 8. Estimate of Left-Turn Vehicles Queued

Figure 9. Intersection Profile Case A

Figure 10. Intersection Profile Case B

Figure 11. Intersection Profile Case C

LIST OF TABLES

Table 1. IDRM Advisory Panel Participants

Table 2. Priority Issues Identified for Knowledge Base Development

Table 3. IDRM Concerns

Table 4. IDRM Models

Table 5. Application of IDRM Models to Evaluate Concerns

Table 6. Values of Dt for Various Intersection Scenarios

Table 7. Minimum Sight Distance on Approach to Traffic Signal

Table 8. Minimum Sight Distance on Approach to Stop Signs

Table 9. Minimum Sight Distance on Approach to Yield Signs

Table 10. Decision Sight Distance (Table III-3 in 1994 Green Book)

Table 11. Skewed Unsignalized Intersection – Additional Clearance Seconds (With Median/Turn Bay on Major Approaches)

Table 12. Skewed Unsignalized Intersection – Additional Clearance Seconds (Without Median/Turn Bay on Major Approaches)

Table 13. Skewed Signalized Intersection – Additional Clearance Seconds (With Median/Turn Bay on Major Approaches)

Table 14. Skewed Signalized Intersection – Additional Clearance Seconds (Without Median/Turn Bay on Major Approaches)

Table 15. Volume Warrants for Left-Turn Lanes

Table 16. Threshold Volumes for Right-Turn Lane

Table 17. Required Deceleration Lengths

Table 18. Weights for Use in Computing the Intersection Conflict Index

Table 19. Design Controls on Difference Between Major - and Minor - Road Slopes

Table 20. Tentative Threshold Values and Types of Safety Advisory Messages for Evaluation of ISD

Table 21. Tentative Threshold Values and Types of Safety Advisory Messages for Evaluation of SSD

Table 22. Tentative Threshold Values and Types of Safety Advisory Messages for Evaluation of Visibility to Traffic Signals

Table 23. Tentative Threshold Values and Types of Safety Advisory Messages for Evaluation of Visibility to Stop Signs

Table 24. Tentative Threshold Values and Types of Safety Advisory Messages for Evaluation of Visibility to Yield Signs

Table 25. Accident Patterns for Increased Emphasis on Particular Intersection-Leg Concerns at Four-Leg Intersections

Table 26.  List of Treatments (Design Improvements and Mitigation Measures) for Intersection Concerns

Table 27. List of Treatments (Design Improvements and Mitigation Measures) for Intersection-Leg Concerns

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