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Guide to Road Design Part 4A: Unsignalised and Signalised Intersections (2017 Edition)

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Publication no: AGRD04A-17 Pages: 142
Published: 07 June 2017


Guide to Road Design Part 4A: Unsignalised and Signalised Intersections provides road designers and other practitioners with guidance on the detailed geometric design of all at‑grade intersections (excluding roundabouts).

This Part contains information for the design of signalised and unsignalised intersections. Guidance is provided on intersection sight distances, including approach sight distance, safe intersection sight distance, and minimum gap sight distance. Left and right turn treatments are outlined including the incorporation of auxiliary lanes at intersections and the use and size of traffic islands.

This third edition contains minor editorial and technical changes throughout the Guide, and substantial parts of Sections 1.4, 3.2, 4.3-4.14, 5.1, 5.2, 6.1, 7.1-7.5, 8, 9 and 10 have been transferred to Guide to Road Design Part 4: Intersections and Crossings – General.

Updates have been made throughout this edition to include new and updated reference material and cross‑references to other Guides. Most figures have been redrawn to provide a consistent appearance. The major updates include:

  • Section 1: Introduction: Updates to road safety, including the Safe System principles.
  • Section 3: Sight Distance: Incorporates additional information relating to safe intersection sight distance and additional description in tables to assist in interpretation.
  • Section 5: Auxiliary Lanes: Section 5.2 (new number), has information included from the commentaries on turning radii and vehicle speeds, and Table 5.4 contains additional information on acceleration lane lengths.
  • Section 6: Traffic Islands and Medians: Information from Appendix D has been included in Section 6.2.


Table of Contents

Summary
1. Introduction
  • 1.1 Purpose
  • 1.2 Scope of this Part
  • 1.3 Design Criteria in Part 4A
  • 1.4 Intersection Safety and the Safe System Approach
  • 1.5 Grade Separation of Traffic Movements
2. Layout Design Process
  • 2.1 Design Process
  • 2.2 Alignment of Intersection Approaches
  • 2.2.1 Horizontal Alignment
  • 2.2.2 Vertical Alignment
  • 2.2.3 Combined Horizontal and Vertical Curves
  • 2.2.4 Superelevation at or near Intersections
3. Sight Distance
  • 3.1 General
  • 3.2 Sight Distance Requirements for Vehicles at Intersections
  • 3.2.1 Approach Sight Distance (ASD)
  • 3.2.2 Safe Intersection Sight Distance (SISD)
  • 3.2.3 Minimum Gap Sight Distance
  • 3.3 Pedestrian Sight Distance Requirements
  • 3.4 Sight Distance at Property Entrances
4. Types of Intersection and Their Selection
  • 4.1 General
  • 4.2 Intersection Types
  • Unchannelised and unflared intersections
  • Unchannelised and flared intersections
  • Channelised intersections
5. Auxiliary Lanes
  • 5.1 General
  • 5.2 Deceleration Lanes
  • 5.2.1 Components of Deceleration Turn Lanes
  • 5.2.2 Determination of Deceleration Turning Lane Length
  • 5.3 Acceleration Lane for Cars
  • 5.3.1 General
  • 5.3.2 Acceleration Distance
  • 5.3.3 Merge Taper Tm
  • 5.4 Acceleration Lanes for Trucks
  • 5.5 Auxiliary Through-lane Design
6. Traffic Islands and Medians
  • 6.1 Raised Traffic Islands and Medians
  • 6.1.1 Raised Islands
  • 6.1.2 Raised Medians
  • 6.1.3 Raised High-entry Angle and Free-flow Left-turn Islands
  • 6.1.4 Simple High Entry Angle Design Process
  • 6.2 Painted Traffic Islands and Medians
  • 6.2.1 General
  • 6.2.2 Painted Medians
  • 6.2.3 Painted Left-turn Islands
  • 6.3 Desirable Clearances to Traffic Islands and Medians
  • 6.4 Road Width between Kerbs and between Kerb and Safety Barrier
  • 6.4.1 General
  • 6.5 Kerb and Channel
  • 6.5.1 General
  • 6.5.2 Kerb and Channel Types
7. Right-turn Treatments
  • 7.1 Design Procedure
  • 7.2 Rural Right-left Staggered T-intersection
  • Basic two-lane two-way road
  • 7.3 Rural Right-turn Treatments – Divided Roads
  • 7.3.1 Two Stage Crossing on a Rural Road
  • 7.3.2 Left-right Staggered T – Divided Road
  • 7.3.3 Back-to-back Right Turns on a Divided Road
  • 7.4 Rural Wide Median Treatment
  • 7.5 Urban Right-turn Treatments – Undivided Roads
  • 7.5.1 Urban Basic Right-turn Treatment (BAR)
  • 7.5.2 Urban Channelised T-junction – Short Lane Type CHR(S)
  • 7.6 Urban Right-turn Treatments – Divided Roads
  • 7.6.1 Channelised Right-turn (CHR) on Divided Urban Roads
  • 7.6.2 Two Stage Crossings on Divided Urban Roads
  • 7.6.3 Seagull Treatments on Divided Urban Roads
8. Left-turn Treatments
  • 8.1 General
  • 8.1.1 Return Radius
  • 8.1.2 Intersection Angle
  • 8.2 Rural Left-turn Treatments
  • 8.2.1 Rural Basic Left-turn Treatment (BAL)
  • 8.2.2 Rural Auxiliary Left-turn Treatment – Short Turn Lane [AUL(S)] on the Major Road
  • 8.2.3 Rural Auxiliary Left-turn Lane Treatment (AUL)
  • 8.2.4 Rural Channelised Left-turn Treatment (CHL) with High Entry Angle
  • 8.3 Urban Left-turn Treatments
  • 8.3.1 Urban Auxiliary Left-turn Treatment (AUL) on the Major Road
  • 8.3.2 Left-turn Treatments for Large Vehicles
9. Signalised Intersections
  • 9.1 Design Process
  • 9.2 Sight Distance
References
Appendix A Extended Design Domain (EDD) for Intersections
  • A.1 General
  • A.2 EDD for Sight Distance at Intersections
  • A.2.1 Application of EDD for Sight Distance at Intersections
  • Compliance with EDD for sight distance at intersections
  • Formulae
  • A.2.2 Base and Check Cases
  • Base cases
  • Check cases
  • Optional check cases
  • A.2.3 EDD Approach Sight Distance (ASD)
  • A.2.4 Observation Times for EDD Safe Intersection Sight Distance
  • A.2.5 EDD Safe Intersection Sight Distance (SISD)
  • Application of the base cases
  • Application of the check cases
  • A.2.6 Sight Distance at Constrained Urban Intersections
  • A.3 EDD for Sight Distance at Domestic Accesses
  • A.3.1 Application of EDD for Sight Distance at Domestic Accesses
  • A.4 EDD for Minor Road Approaches
  • A.5 EDD for Intersection Turn Treatments
  • A.5.1 Intent of EDD Turn Treatments
  • A.5.2 Use of EDD Turn Treatments
  • A.5.3 General Considerations
  • A.5.4 Minimum EDD Channelised Right-turn Treatment for Two-lane Two-way Roadways without Medians
  • A.5.5 Minimum EDD Channelised Right-turn Treatment for Roadways with Medians
  • A.5.6 Minimum EDD Auxiliary Left-turn Treatment
  • A.6 EDD Treatment of a Constrained Left-turn Radius
  • A.7 EDD for Existing Channelised Four-way Intersection – Right-turn CHR
  • A.8 EDD for Median Widths
  • A.9 Adverse Crossfall for Turning Movements
Appendix B Truck Stability at Intersections
  • B.1 Introduction
  • B.2 Lateral Friction Force on Vehicles
  • B.3 Other Factors that Affect Truck Stability
  • B.4 Critical Turning Speeds for Trucks in Intersections
Appendix C Swept Paths for Road Trains at High Entry Angle Left-Turn Treatments
  • C.1 Introduction
  • C.2 Examples of Vehicle Swept Paths
  • C.2.1 Normal Treatment
  • C.2.2 Alternative Treatment
  • C.3 Detailed Examples from Main Roads Western Australia

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