By Robert Connors, PE, CCS
Design-build (D-B) proponents laud the construction delivery method as a suitable way for complex projects to accelerate completion, contain liability for cost overruns, and shift operational risks. Potential disadvantages for owners include less control, increased need for earlier and timely owner decisions, and resistance from those unfamiliar with the delivery method.
Properly prepared bridging documents advance owner goals to:
- select the best D-B team by establishing a clear and competitive procurement process;
- establish what they are buying through project definition;
- maximize desired advantages and minimize disadvantages of the D-B process; and
- allocate risks in order to optimize the owner’s risk/cost tradeoff.
Bridging documents convey design/construction requirements to D-B teams bidding the project. They include a summary of work, technical requirements, plans, project constraints, reference materials, and contractual requirements. Empirical evidence suggests key aspects to consider when preparing bridging documents include project definition, risk allocation, defining the procurement process, and following best practices.
To ensure they get what they bought, public agencies typically require more project definition than private owners in bridging documents. Private owners have greater influence when refining the project definition in the final design, because future work will likely be awarded on past performance and personal relationships. Public agencies, on the other hand, have less leverage with D-B contractors due to public bidding laws. Public agencies also have internal customers such as construction, engineering, and maintenance departments that often prefer a higher level of definition and control.
The project definition:
- provides a basis for bids and agreement;
- identifies technical issues, risks, and project constraints;
- conveys lifecycle criteria;
- avoids unnecessary owner commitments;
- maximizes innovation opportunities; and
- establishes quality assurance criteria.
Conveying required elements
Defining scope and technical requirements, the project agreement is the sole document defining contractual requirements. Design elements ‘required’ by the owner must be identified as such.
The bridging documents often include a technical design concept presenting the project scheme and layout. The technical design concept articulates ‘one way’ of designing the project, but not ‘the only way.’ It provides proof of feasibility within the project constraints. The technical design concept represents a five to 30 percent effort level, but varies by discipline and project. It can be used to estimate construction costs. The technical design concept is issued by bidders as a ‘no-reliance’ document, but it should not contain errors or be misleading.
The technical design concept, or portions of which are defined as ‘required’ in the project agreement, is used to define scope requirements and measure compliance.
To maximize innovation opportunities, bridging documents employ performance criteria, which are measurable performance attributes of products that define their suitability for installation on a specific project. The more the project description is expressed in performance criteria, the more flexibility the design-builder has in creating an efficient final design.
As an example of performance criteria, the Ottawa Light-rail Transit (OLRT) is a complete new system including tunnels, railway, stations, maintenance facilities, vehicles, and a 30-year maintenance term. The bridging documents for this Canadian project established light-rail system performance criteria of 24,000 people per hour (pph). This allowed the proposing D-B teams to find the most efficient combination of vehicle capacity, headway, and station capacity to meet the performance criteria.
Innovation in design-build projects is encouraged when performance criteria is used. Collaboration between the designer and builder also results in innovation. As long as the bridging documents clearly define the project requirements and performance criteria and tests, the owner gains value.
Under a traditional design-bid-build construction delivery model, the owner has separate contracts with the designers and the builder—this creates a liability gap. The designeris responsible to meet a standard of care. The builder is responsible to build to plans and specifications. In D-B, the owner has a single contract and a single point of contact.
Project cost is the critical owner and proposer concern. Bridging documents are used by the owner to develop a construction cost estimate. An accurate bridging cost estimate is essential for the owner’s budgeting, risk analysis, value analysis, and financial models. Bridging documents are also used by proposers to develop their cost/bids. The overall level of design in bridging documents (and the level of design in specific project elements) is driven by what information is necessary to get an accurate bid and cost estimate.
Bridging documents provide proof of feasibility within the project constraints. On longer, more complex projects, and those with long lead items and schedule constraints, it is important to develop an accurate schedule with the bridging documents. The design-build approach results in accelerated project completion—the bridging documents must capture this value for the owner through setting accelerated (but still feasible) milestone and completion dates for the project in the bridging documents.