Value of a Progressive Design Build vs. Design Bid Build Delivery Model for Rehabilitation Projects

Abstract

In the civil construction industry, the choice between a Progressive-Design-Build (PDB) contract and a Traditional Design-Bid-Build (DBB) contract can significantly impact project outcomes. This paper explores two sewer rehabilitation project case studies in the Pacific-Northwest (Washington, USA) for King County: a traditional DBB style contract (Interbay Conveyance Rehabilitation and Odor Control project) and a PDB style contract (Eastside Interceptor Section 8 rehabilitation project). The focus of the paper is to present how and when a PDB contract can impact and benefit civil rehabilitation projects drawing on shared perspectives and learnings from the Owner, Contractor and Design Consultant. A PDB contract integrates design and construction, fostering collaboration among the Owner, designer, and contractor from the start. This allows for real-time adjustments, cost estimations, and value engineering, enhancing efficiency and reducing risks. Early-contractor-involvement ensures constructability reviews and feasibility assessments, leading to innovative solutions and optimized designs. This collaborative environment often results in faster project delivery as design and construction activities can overlap. The PDB contracting model has seen widespread use in North America over the past two years and is likely to remain popular in the future. In contrast, the DBB model follows a well-established, sequential process where the design is completed before construction begins. This approach provides clear delineation of responsibilities and allows for competitive bidding, which can help drive cost efficiency and transparency. DBB is particularly effective for projects with well-defined scopes and minimal anticipated changes, where the design can be fully developed in advance. Its structured nature supports thorough planning and documentation, which can be advantageous for regulatory approvals and internal stakeholder alignment. While it may not offer the same level of flexibility, DBB remains a reliable and widely used method for delivering infrastructure projects with predictable requirements.