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Road Design

Cover of Guide to Road Design Part 4C: Interchanges
Guide to Road Design Part 4C: Interchanges
  • Publication no: AGRD04C-23
  • ISBN: 978-1-922700-88-9
  • Published: 29 May 2023
  • Edition: 2.1

Guide to Road Design Part 4C: Interchanges provides guidance on the geometric design of interchanges on freeways/motorways and on major arterial roads.

The Guide covers the design of interchanges between freeways and arterial roads; two freeways; and two major arterial roads. It covers the geometric design of all the elements of an interchange including the alignment and cross-section of the freeway in the vicinity of the interchange, the intersecting road and the ramps; merge and diverge ramp terminals at the freeway; and ramp terminals at the intersecting road.

Edition 2.1 contains editorial and technical changes to sections 2.3, 4.1, 4.2, 5.2.1, 5.2.2, 7.4, 10.3, 11.2, 11.3.3, 11.4.3, 13.1, 14.1, and 15.3. It also contains new guidance in Section 3.2.3 for grade-separated intersections, Section 11.2.5 for exit ramps near tunnel sections and Section 11.3.7 for entry ramps near tunnel sections.

Edition 2.0 contains minor editorial and technical changes to Sections 1.3, 1.4, 1.8, 3.2, 4.9 (new), 9.2, 10.1, 11 and 17.3. Updates have been made throughout this edition to include new and updated reference material and cross-references to other Guides, including:

  • Section 1 Introduction: updates to road safety including the Safe System principles; and additional information on design objectives and staged development.
  • Section 3 Forms of Interchange: additional information on factors that may influence the type of interchange.
  • Section 4 Structures: additional section providing information on safety screens.
  • Section 9 Vertical Alignment: additional information on criteria to be considered for grading at a cross-road.
  • Section 10 Ramp Terminals at Major Roads: amending the longitudinal grade of a minor road to not exceed 2%.
  • Section 11 Ramp Terminals at the Major Road: additional information to expand the range of speeds shown in Table 11.2 and Table 11.3.
  • Section 17 Other Considerations: additional section on oversized and high wide load corridors.
  • 1. Introduction
    • 1.1 Purpose
    • 1.2 Scope of this Part
    • 1.3 Road Safety
    • 1.4 Road Design Objectives
    • 1.5 Traffic Management at Interchanges
    • 1.6 Safety Performance of Interchanges
    • 1.7 Traffic Capacity of Interchanges
    • 1.8 Staged Development of Interchanges
      • 1.8.1 Staging Interchange Development
      • 1.8.2 Flexibility and Constructability
  • 2. Design Considerations Process and Principles
    • 2.1 General
    • 2.2 Design Considerations
      • 2.2.1 Design Information
      • 2.2.2 Design Controls and Criteria
      • 2.2.3 Stormwater Drainage
      • 2.2.4 Landscape Development
      • 2.2.5 Public Transport Facilities
    • 2.3 Design Process
      • 2.3.1 Review Planning Reports
      • 2.3.2 Design Brief
      • 2.3.3 Preliminary Design
      • 2.3.4 Detailed Design Stage
    • 2.4 Principles
      • 2.4.1 Interchange Elements
      • 2.4.2 Interchange Uniformity and Spacing
  • 3. Forms of Interchange
    • 3.1 Traffic Considerations
    • 3.2 Other Considerations
      • 3.2.1 General
      • 3.2.2 Underpass or Overpass
      • 3.2.3 Grade-separated Intersection
  • 4. Structures
    • 4.1 General
      • 4.1.1 Types of Structure
    • 4.2 Form of Structure
    • 4.3 Cross-sections on Bridges
    • 4.4 Pedestrian/Cyclist Grade Separations
      • 4.4.1 General
      • 4.4.2 Safety Barriers at Pedestrian Bridges
    • 4.5 Culverts
    • 4.6 Retaining Walls
    • 4.7 Wildlife Crossings
    • 4.8 Services on Structure
    • 4.9 Safety Screens
  • 5. Cross-Section
    • 5.1 Major Road and Minor Road
    • 5.2 Ramp Cross-section
    • 5.2.1 Number of Lanes on Ramps
    • 5.2.2 Ramp Lane Widths
    • 5.3 Clearances on Major Road
  • 6. Design Speed
    • 6.1 General
    • 6.2 Major Road
    • 6.3 Minor Road
    • 6.4 Ramps
      • 6.4.1 Ramp Design Speed
      • 6.4.2 Other Considerations
  • 7. Sight Distance
    • 7.1 General
    • 7.2 Stopping Sight Distance on the Major Road and Minor Road
    • 7.3 Exit Ramp Nose
    • 7.4 Entry Ramp Nose
    • 7.5 Safe Intersection Sight Distance
  • 8. Horizontal Alignment
    • 8.1 Major Road
    • 8.2 Minor Road
      • 8.2.1 Curvature
      • 8.2.2 Spread Diamond Interchanges
    • 8.3 Ramps
      • 8.3.1 General
      • 8.3.2 Geometric Requirements
      • 8.3.3 System Interchanges
      • 8.3.4 Service Interchanges
  • 9. Vertical Alignment
    • 9.1 Major Road
      • 9.1.1 Grading Options
      • 9.1.2 Grading Controls
    • 9.2 Minor Road
      • 9.2.1 Closed Diamond
      • 9.2.2 Spread Diamond
    • 9.3 Ramps
      • 9.3.1 Ramp Gradients for System Interchanges
      • 9.3.2 Ramp Gradients on Service Interchanges
  • 10. Ramp Terminals at Major Roads
    • 10.1 Ramp Terminal Locations
    • 10.2 Ramp Alignment at Minor Road Terminals
      • 10.2.1 Exit Ramp Alignment at Minor Road Terminals
      • 10.2.2 Entry Ramp Alignment at Minor Road Terminals
    • 10.3 Ramp Terminal at Minor Road
  • 11. Ramp Terminals at the Major Road
    • 11.1 General
    • 11.2 Exit Ramps
      • 11.2.1 Single-lane Exits
      • 11.2.2 Two-lane Exits
      • 11.2.3 Exits to Two High-speed Roadways
      • 11.2.4 Lane Drop at an Exit
      • 11.2.5 Exit Ramps near Tunnel Sections
    • 11.3 Entry Ramps
      • 11.3.1 General
      • 11.3.2 Single-lane Entry
      • 11.3.3 Entry with Auxiliary Lane
      • 11.3.4 Two-lane Entry
      • 11.3.5 Loop Ramps
      • 11.3.6 Merging of High-speed Major Roads
      • 11.3.7 Entry Ramps near Tunnel Sections
    • 11.4 Ramp Traffic Signals
      • 11.4.1 General
      • 11.4.2 Capacity Analysis
      • 11.4.3 Geometric and Layout Design
  • 12. Ramps on Two-Lane Two-Way Freeways
  • 13. Pedestrians
    • 13.1 General
    • 13.2 Bus Passengers
  • 14. Cyclists
    • 14.1 General
    • 14.2 Treatment at Interchanges
      • 14.2.1 Cyclists Required to Exit and Re-enter Freeway
      • 14.2.2 Grade Separation of Ramps for Cyclists
      • 14.2.3 Alternative Routes
  • 15. Pavement Markings, Signs and Lighting
    • 15.1 General
    • 15.2 Key Considerations
    • 15.3 Lighting of Interchanges
  • 16. Landscaping and Street Furniture
    • 16.1 General
    • 16.2 Landscape Development
    • 16.3 Road Safety
  • 17. Other Considerations
    • 17.1 Access in the Vicinity of Interchanges
      • 17.1.1 Access to the Freeway
      • 17.1.2 Access to the Minor Road
    • 17.2 Service Centres
    • 17.3 Oversized Loads and High Wide Load Corridors
  • References
  • Appendix A Example of Ramp Speed Analysis
  • Appendix B Ramp Terminal Location
  • Appendix C Examples of Ramp Signal Layouts
  • Commentary 1
  • Commentary 2
  • Commentary 3
  • Commentary 4
  • Commentary 5
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