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I-64/US 15 Diverging Diamond Interchange (DDI) Zion Crossroads. Louisa County, Virginia.

WRA was the Owner Representative for VDOT on this $6.8 M interchange improvement design-build project.

WRA prepared an Interchange Modification Report (IMR) to determine recommended improvements that addressed existing safety deficiencies and accommodated planned development and future traffic volume increases.  VDOT selected the DDI alternative as the most efficient way to address safety and capacity needs. It also provided a solution within the existing right-of-way and did not require reconstruction of the Route 15 bridge over I-64, costing less than half compared to other alternatives under consideration. WRA developed the 30% plans on an accelerated schedule, the RFQ and RFP contract documents, and provided design review services during the delivery phase. This was the first DDI constructed in Virginia.

Diverging Diamond Interchange
Project Highlights


WRA performed extensive research of best practices in various states with regard to the design, operation, and implementation of DDIs. The DDI alternative provided extremely efficient movement of traffic through the interchange due to the simple, two-phase traffic signals and balancing of competing left-turn movements. Preliminary Field Inspection plans were prepared in five weeks on an accelerated schedule in order to hold a Public Meeting.


As part of the IMR development that was approved by VDOT and FHWA, WRA prepared a detailed traffic simulation using VISSIM. Base condition models were developed and calibrated to match existing traffic volume and travel time data throughout the corridor. Average and maximum queue lengths were also compared to ensure the model was predicting reasonable results. Simulation models were then developed for each of the proposed interchange alternatives under consideration. Upon selection of the DDI, a detailed three-dimensional video was developed using VISSIM to gain public acceptance.