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Existing Conditions
Project improvements were necessary due to severe traffic congestion within the interchange area. The configuration of the existing interchange resulted in closely spaced signalized intersections and inadequate vehicle storage capacity.
Interchange Improvements
The project widened College Boulevard under SR 78 and realigned Vista Way, a major frontage road adjacent to the freeway. A new westbound on-ramp to SR 78 was constructed and a significant realignment of the westbound off-ramp from SR 78 was completed.
One signalized intersection was eliminated which increased the number of through lanes and turn lanes on College Boulevard and Vista Way, and improved vehicle storage capacity.
Structures
Interchange modifications included widening the simple-span box girder undercrossing structure. The widened portion of the structure was designed to be built on elevated falsework, above finish grade, and ultimately lowered into place. This system allowed the selection of a cast-in-place concrete structure type, matching the structure type of the existing undercrossing.
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Traffic Management Plan
A Traffic Management Plan (TMP) was developed to assist with anticipated road and ramp closures during construction. Of particular importance was the nearby Tri-City Hospital that required unrestricted access 24-hours per day. The TMP addressed procedures for notification of emergency personnel on a daily basis regarding road closures and detours. District 11 Traffic Operations reviewed and approved the TMP and worked to insure that proper notifications were conducted during construction.
Retaining Walls
The widening of College Boulevard under SR 78 required the design of tie back retaining walls at each undercrossing abutment. The tie-back retaining walls received a cast-in-place concrete fascia with architectural treatment to improve the visual aesthetics of the walls. District 11 Landscape Architecture provided review and approval of the architectural design proposed by Dokken Engineering.
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