Wednesday, August 10, 2016

#WZW Diverging Diamond Interchange in Junction City

The interchange for I-70 and U.S. 77, with a diverging diamond interchange. 
A differently designed interchange will soon be coming to the I-70/U.S. 77 interchange on the west side of Junction City. A diverging diamond is a type of interchange in which two direction of traffic on the non-freeway road cross to the opposite side on both sides of the bridge at the freeway.

The project was let earlier this spring and construction begins this summer. How traffic passes through the DDI is unconventional, but easily understood by drivers unfamiliar with the design. This location was chosen because of it's importance to freight movement for trucks.

The DDI has many advantages over a traditional Diamond Interchange when dealing with high traffic volumes and a high percentage of tractor-trailers by reducing the number of conflict points. The benefits are listed below.
Safety Benefits
  • Fewer conflict points (14 for DDI, 26 for conventional)
  • Conflict points spread out throughout interchange
  • Better sight distance at turns
  • Virtually no driver confusion (FHWA study and new DDI observations in Springfield, MO)
  • Traffic calming features when desired
  • Wrong way entry to ramps extremely difficult
  • Pedestrian crossings are shorter
Operational Benefits

  • Unique phase combinations
  • “Free” or simple left and right turns from all directions
  • Increases left turn lane capacity without needing more lanes
  • Only two phases needed, shorter cycle length
  • Lanes with multiple assignments in all directions
  • Better storage between the ramp terminals
  • More functional during a power outage
  • U-turns from highway are accommodated well
  • Better signal network synchronization

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