An evening aerial view (taken by drone, not over live traffic) shows the crossover points to the left side of traffic at Virginia’s I-95/Route 630 DDI interchange. Photo: Dewberry
California’s first DDI, soon to open in Manteca, has benefitted from a rigorous partnering process during construction. Photo: Rob Shackelford, courtesy of Dewberry.
school that visitors could walk along, pretending they were in a car and mimicking the motions of the diverging diamond interchange. The exhibit included graphics of all of the highway signs so that visitors could see what the updated signage would look like, where the traffic signals would be, and how it would operate. California’s First Diverging Diamond Interchange On the West Coast, construction is underway on California’s first di- verging diamond interchange for the City of Manteca’s Union/SR120 Interchange Project in Manteca. Here, city administrators determined that the configuration would be the optimal solution to improve its State Road 120/Union Road interchange. Designed by the consulting firm of Mark Thomas and Company and built by local contractor Teichert Construction, the interchange will significantly reduce potential accident locations and improve traffic flow. The existing interchange has 26 po- tential conflict points while the DDI design reduces this to 14. Dewberry has provided construction management services for the project. Staging is critical to the success of diverging diamond interchange projects, and this has proven to be the case with the construction in Manteca. The need to relocate overhead utilities delayed the project by approximately six months. Staging can be complex where alignments overlap, requiring a significant amount of field and public coordina- tion, which was in this case complicated by the utility delay. Additional staging challenges in the electrical work, drainage, and signage com- ponents also had to be coordinated in real-time to keep all disciplines moving forward. Another major challenge involved moving the excess dirt on the proj- ect site. The proposed plan including moving 275,000 cubic yards of imported borrow—the dirt that is delivered to help construct the site. To resolve the issues of the delay and removal of excess dirt from the project, our team coordinated with the city’s Department of Public Works to re-sequence the staging. This included closing one side of the over-crossing bridge as well as the westbound on-ramp and the eastbound off-ramp. While this created detours for commuters, the de-
cision enabled us to combine three phases of the construction process into one. This resulted in several benefits: • Reducing the offhaul of roadway excavation material • Removing the inefficient balancing of dirt in each state of construction. We reduced the transported borrow quantity from 275,000 cubic yards to 225,000. • Trimming four months from the project schedule • Providing a roughly $350,000 credit to the city following a value engineer- ing change proposal (VECP) A VECP recommends a cost and/or time-saving measure that results in shared savings with the owner. In this case, the VECP, which ulti- mately yielded both cost savings as well as the four-month reduction in the schedule, was initiated by the contractor, reviewed by our CM team, and then cleared with the city’s risk and public relations depart- ments. Ultimately, this effort mitigated much of the utility delay. A Partnering Process The successful process to address the challenges of the SR 120/Union Road interchange project in Manteca can be attributed in large part to a formal partnering relationship involving a professional facilitator. We maintained a strong relationship with the contractor, kept an open dialog with all parties, and encouraged collaboration and regular com- munications. This breakthrough project should soon serve as a model for other diverging diamond interchange projects in California.
STEVE KUNTZ, PE, DBIA, is a vice president in the Fairfax, Virginia, office of Dewberry. HOWARD ZABELL, PE, is an associate vice president and construction services manager in the Rancho Cordova, California, office of Dewberry.
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october 2020
csengineermag.com
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