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-15
Double 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:
http://www.udot.utah.gov/sr92/
 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

8. 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

9. 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

10. 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

11. 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