Four-level Freeway-to-Freeway Interchange
Dokken Engineering was hired by the San Diego Association of Governments (SANDAG) to prepare the Plans, Specifications and Estimate (PS&E) of a 4-level freeway-to-freeway interchange including a portion of the State Route 125 (SR 125) Corridor. The interchange connects the 6-lane SR 125 and the existing SR 94 freeways. The project is the largest consultant designed interchange in San Diego County. To ensure funding deadlines were met, Dokken Engineering accelerated the PS&E schedule.  The project plans, consisting of 1024 sheets, were approved in 31 months – nearly 5 months ahead of the original schedule.

Consensus Building
Built in an existing urban setting, public involvement was critical to the overall success of the project.  Through public workshops, Dokken obtained valuable input from the local community. Visual and noise impacts were of particular concern to residents. Visual impacts were minimized through a combination of bridge architecture and attractive details for sound and retaining walls, including plantable designs.  State-of-the art masonry/glass sound walls were used to preserve resident views while providing effective barriers to traffic noise.

Preliminary Engineering
Preliminary engineering was completed to establish roadway geometrics and profiles, determine the location of a major frontage road, and determine required right of way.  The results of our preliminary engineering, completed concurrently during the PS&E, was to shift portions of the interchange to avoid acquiring a controversial business, reduce the cost of the proposed structures by over $6 million, and add access from Spring Street to southbound SR 125.

Bridge Design
Dokken designed 7 major bridges and 4 Mechanically Stabilized Embankment (MSE) retaining walls.  The total length of the bridges is 9,900 feet, which contain more than a half-million square feet of deck; some of the columns exceed 100 feet in height.  Special features of the bridges include 3 outrigger bent caps, and the use of site specific seismic criteria.  High seismic loads from the nearby Rose Canyon Fault were handled with advanced dynamic analysis techniques and innovative seismic isolation column casings. Advanced  3-D modeling techniques were used in the design of column and bent cap reinforcing, eliminating many conflicts in these highly-congested areas of reinforcement.

Drainage Design
Prior to the completion of the project, the intersection of Broadway and Sweetwater Road was often flooded during major storm events. As part of the interchange drainage design, a detention basin was designed to eliminate the recurring flooding. The design involved completing a complex hydraulic analysis including routing peak flows through multiple detention basins, analyzing split flows, and evaluating existing, overloaded storm drain systems. Dokken developed a system of storm-water diversion and retention facilities assuring that the existing facilities would not be continually flooded during major storms.

Engineer’s Estimate
An Engineer’s Estimate was prepared for each PS&E submittal.  Dokken Engineering’s final estimate was within 4.8% of the contractor’s estimate, providing strong confirmation that our cost estimates had been accurate throughout the PS&E process.

Design Support During Construction
For over 3 years, Dokken staff provided daily support during construction.  At the conclusion of construction, evaluated items included contract plans, bid items, quantities, staging and design support.  A Design/ Construction Features Memorandum (project evaluation form) dated April, 2006, evaluated both Caltrans and Dokken Engineering performance was completed.  Comments on the performance of Dokken included:

• “The Resident Engineer (RE) Book was informative and very complete and organized.”
• “Structure staging was thought out and the contractor followed the prescribed staging plans for this work.”
• “All bid items adequately reflected the work to be done on this project.” 
• “Project staging was well thought out considering the magnitude of the contract while keeping existing highway and local street traffic moving.”
• “Support on this consultant designed project was excellent. Both the oversight PE and consultant PM were responsive to our construction inquiries.”