Launch Slideshow

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Design-build vs. CM/GC

Design-build vs. CM/GC

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    Source: Utah DOT

    'All-parties' risk assessment lowers project price 27%: Utah DOT convened four “opinions of probable construction cost” (OPCC) workshops for a multimodal transportation system. The designers' assessment of risk (OPCC1) was, as usual, lower than the contractor's. At 30% design completion, OPCC2A included the contractor's assessment, which factors in unknown risks. OPCC3 and 4 focused on mitigating risks. If awarded at 30% design — when a contractor is selected in design-build — the Mountain View Corridor would have cost $126 million more than the final $223 million price tag. Unlike design-build, the owner rather than the contractor keeps the savings.

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    Source: Utah DOT

    Utah DOT found that with the CM/GC approach, change orders and overruns are 40% to 60% less than with design-bid-build. In addition, it achieves a cost savings of 6% to 12% for innovation and 15% to 22% for risk management.

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    Source: Utah DOT

By Reuel Adler, PE

The manufacturing world has proved that a high-quality product can be made for less money using a streamlined process. “Lean manufacturing”— a term used to describe a production process that eliminates waste — replaces the stop-and-go process of a classic batch-and-queue system with a smoother, continuous-flow system. Proponents say the process preserves value while doubling productivity.

The same principle can be applied to road construction. Like lean manufacturing, construction manager/general contractor (CM/GC) uses a team approach that incorporates the contractor's point of view into the project much sooner than design-bid-build. The contractor is hired early enough to contribute expertise that prevents design errors, and to order materials much earlier so construction begins sooner. The early start coupled with early procurement eliminates up to a year in construction time.

Because the contractor has more time to become familiar with new construction methods, such as accelerated bridge construction, the owner — which retains control of design decisions — can deploy innovations without a significant cost increase for risk.

Overlapping design, construction phases

The advantages of CM/GC are speed, brevity, and control. You don't need a design package to move forward on a project, as required in traditional design-bid-build. You also don't need a performance specification of hundreds to thousands of pages to hire the contractor, as required in design-build. You only need to define your goals and evaluation criteria. This shortens acquisition time.

Early inclusion of the contractor helps the design phase to transition seamlessly into the construction phase. For example, we used CM/GC for an accelerated bridge construction project over I-215 in Salt Lake City. This allowed the contractor to order girders — typically a long lead-time item — before design began. The contractor also developed the construction schedule during design, which minimized lane closures and other negative impacts to the public.

However, the real time savings was a result of building the bridge offsite and moving it into place over a weekend. It was the first time we've used this method and CM/GC gave the contractor time during design to figure out how to do this.

Adjustments that can be made during design include special considerations for local government needs and incorporating more public involvement. Unlike design-bid-build, CM/ GC enables the contractor and designers to determine right-of-way and utility issues during design and focus on ways to reduce their impact on the overall schedule.

A word of caution: Shortening the design phase minimizes the effectiveness of CM/GC because the contractor has less time to provide input. In fact, the design phase is generally longer to accommodate contractor feedback.


Innovations and risk avoidance