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Introduction to the Diverging Diamond Interchange

Introduction to the Diverging Diamond Interchange. Alaska DOT Quarterly Design Meeting Anchorage, AK March 30, 2010. Steve Speth, P.E., PTOE Professional Associate HDR Engineering. Presentation Purpose. Background / History Site Choice Considerations Traffic Operations Design Safety.

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Introduction to the Diverging Diamond Interchange

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  1. Introduction to the Diverging Diamond Interchange Alaska DOT Quarterly Design Meeting Anchorage, AK March 30, 2010 Steve Speth, P.E., PTOE Professional Associate HDR Engineering

  2. Presentation Purpose • Background / History • Site Choice Considerations • Traffic Operations • Design • Safety

  3. Background/History • What is a DDI? • Why build a DDI? • How many DDIs have been built? • Where are they being considered?

  4. DDI Concept Overview Source: Missouri Department of Transportation

  5. Background/History • Why build a DDI? • Improve Capacity for Interchange with high turning movements • Minimize Bridge Costs • Improve Safety

  6. Background/History • What is a DDI? • Why build a DDI? • How many DDIs have been built? • Where are they being considered?

  7. Existing Locations

  8. Existing Locations

  9. Proposed DDI Locations • Missouri – 7+ locations • Illinois – 2 locations • Kentucky – 5 locations • Utah – 7+ locations • New Mexico – 2+ locations • California – 1 location • Oregon – 1 location • Ohio – 2+ locations • Florida, New York, North Carolina, Nebraska, Tennessee, Wyoming, Colorado…

  10. Site Choice Considerations • The DDI is not the perfect solution for every situation • Things to consider: • Mainline and crossroad alignment • Bridge Height Restrictions • Right-of way constraints • Access control • Nearby signals • Traffic volumes – High Through Volume on cross-street

  11. Traffic Operations • Must be analyzed with Simulation (VISSIM) • Delay is decreased dramatically (generally >50% decrease) • When doing conceptual studies of interchange types, the capacity of 5 lane DDI has been comparable to an 8 lane Diamond or SPUI • The higher the turning traffic, the more dramatic the benefit for the DDI – we have had studies where a 4 lane DDI has outperformed an 8 lane Diamond

  12. Traffic Operations • Why are the operations so much better? • Less Conflict Points = better operations • Less “Crossing Movements” • Traffic Signalization Benefits (shorter cycle, less phases, less lost time) • Freeway operations are improved • “Platooning” of vehicles onto the freeway are reduced • Speeds from the ramp are more consistent • Can be a significant improvement

  13. Design Considerations • Profiles and Grade Separation • Crossing Intersection Angle • Crossroad to Freeway Intersection Angle • Ramp Terminal Separation Distance • Right-of-Way • Access Control • Design Vehicle/Lane widths

  14. Design Considerations • Design Speed and Reverse Curvature • Signing and Striping • Glare Screening • Bicycle and Pedestrian Treatments

  15. Design • Are there design standards for DDIs? • What is the design speed of the reverse curves on the crossroad through movement? • What is the optimum intersection angle of the crossing through movements? • Are there standards for signing and striping?

  16. Design Elements Interior Angle Additional Striping

  17. Safety • Is the DDI safer or is it a safety risk? • Can bicycles and pedestrians safely traverse a DDI?

  18. Conflict Points

  19. Conflict Points

  20. Conflict Points

  21. Safety • Is the DDI safer or is it a safety risk? • Can bicycles and pedestrians safely traverse a DDI?

  22. Bicycles

  23. Pedestrians

  24. Contact Information Steve Speth, P.E., PTOE Professional Associate HDR Engineering 24954 Highway 395 South Canyon City, OR 97820 steve.speth@hdrinc.com

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