Project Delivery Systems: CM at Risk, Design-Build, Design-Bid-Build

Design and construction cost growth was least (best) for the D-B method, approximately 2.4% (median), less than half that for the D-B-B method and approximately 35% lower than experienced by CM at risk projects. The frequency of D-B method projects experiencing >5% cost growth was also much lower than projects using other methods saw. (RS133-1, p. 6)
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Design and construction schedule growth was highest (worst) for D-B-B projects, at about 4.4% (median). Median schedule growth for D-B and CM at risk projects was right at 0%. The frequency of CM at risk method projects experiencing >5% schedule growth was lowest, followed by D-B projects; schedule growth was highest for D-B-B projects. (RS133-1, p. 8)
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Median design and construction speed, measured as square feet completed per month, was highest for D-B projects and was over twice that achieved by D-B-B projects and more than 50% higher than that achieved by CM at risk projects. (RS133-1, p. 9)

Based on seven different measures of “quality,” all three delivery methods on average met or exceeded customer expectations. Within the subtle differences that existed, D-B scored overall higher than the other methods, with D-B-B trailing slightly. (RS133-1, p. 11)

The performance advantages for the D-B method were greater on private sector projects than for public sector projects. The greater flexibility in private sector bidding and contractor selection processes was the most common reasons cited for the greater effectiveness of D-B methods in the private sector. (RS133-1, p. 21)