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  • 1. I-15/Timpanogos Highway (S.R. 92) Diverging Diamond Interchange (DDI) Retrofit(Now Called Double Crossover Diamond (DCD) by FHWA) May 9, 2012 Michael Lasko, PE Brad Hartman, PE Brian Michels, PE 801-350-5200
  • 2. Timpanogos Highway (SR-92)/I-15Double Crossover Diamond Interchange (DCD) Retrofit Replace existing tight diamond I/C to a double crossover diamond I/C  Public Outreach – Design Development and Construction  Geometric footprint and drainage to fit within existing I-15/SR-92 right of way  Traffic Operations  Minimize impacts to utilities  Signing, Striping, and Traffic Signals  Maintenance of Traffic during construction
  • 3. Public Outreach – Design Through Construction Key Part of the Team Public Outreach Team attended design and construction coordination meetings  Enabled better public awareness in advance of and during construction Website: Design/Build Liaison
  • 4. Roadway Design Benefit/Cost – 15+ yrs at $7.9M Driver Perception  Channelization, Sight lines, Barriers, Curbing, Signage, Glare Match Existing Infrastructure (ie ramps, structures) I-15 over SR-92 Vertical Geometry Accommodation for Pedestrian Movements Utilize Existing Pavement  Enabled more efficient MOT setups during construction  Minimized construction costs
  • 5. Traffic Operations FHWA Interchange Access Change Request Acceptance  Geometrics and Signing Plans and Traffic Models Travel Demand Model Future Forecasts  Affects operations, geometrics, storage Utilize Right Modeling Tools  Synchro – Lower cost/Less Effective VISSIM – Higher cost/Very Effective Maintenance of Traffic  Iterative process – MOT Options vs. Modeling/Contract Requirements Two Phase I/C Results in Better Efficiency  Careful consideration required with adjacent intersections  2030 PM Peak SB Ramp Terminal 45% Delay reduction (75s to 41s)
  • 6. Drainage Design Quick Facts Challenges & Lessons Learned  Existing flat grades  Unique geometry  Design standards  Design flexibility Photo courtesy UDOT  Utilities  Collaboration and documentation
  • 7. Minimize Utilities Impacts Complete Interlocal Agreements  Continual coordination with utility operators Pothole and survey existing utilities prior to design Develop utility plan Utility coordinator/Engineer
  • 8. Signing, Striping, Traffic Signals  Signing Balance  Avoid over signing the DCD  Keep signing simple  Manage Vehicle Throughput and I/C Capacity  Consistency w/Operational Analysis  Stop bar placement, Ramp Meters, Shoulders/Shy Distances  Lane widths  Speed  Involve Region Traffic Signal Inspector  Signal Head Placement
  • 9. Maintenance of Traffic during Construction Conduct dry runs and brainstorming sessions with Contractor, UDOT, Designer Minimize impacts to LOS by utilizing night time/weekend construction operations Utilize operational efficiencies of DCD as soon as possible Utilize temporary elements Be diligent and flexible during construction activities
  • 10. Summary Double Crossover Diamond Retrofits Benefits:  Maximizes Traffic Operations at a Lower Cost • FHWA and UDOT Supports the use of DCD Retrofits  Reduces Travel Delays  Extends Interchange Life  Improves Safety – Drivers are More Perceptive  Other States Following UDOT’s Lead • Ohio, Illinois, Kansas