Exploring the impact of project size on design-bid-build and design-build project delivery performance in highways

The highway construction industry has been increasingly using design-build (D-B) project delivery because of its documented benefits. Only limited studies, if any, have compared D-B and traditional design-bid-build (D-B-B) project performance based on the size of projects. The existing gap was addressed by investigating the cost growth, schedule growth, and construction intensity of highway projects delivered under D-B-B and D-B with the project sizes ranging from $2 million to greater than $100 million. These projects were collected from six state departments of transportations in the U.S. with mature D-B programs. Several statistics tests including t-test, Welch’s test, and Mann–Whitney U-test were used to analyze 3888 completed highway construction projects. The results show that D-B produced a lower cost growth than D-B-B in the project size of over $10 million while D-B-B projects had lower cost growth than D-B projects in the project size from $2 million to $10 million. D-B projects also produced less schedule growth than D-B-B projects across all groups of project size. D-B-B projects had a faster work pace than D-B projects in the project size from $2 million to $10 million. The findings contribute to the project delivery body of knowledge by reporting statistically empirical comparisons between D-B-B and D-B project performance controlled by the project size. The findings may help highway agencies better understand how D-B performs under the different sizes of projects in terms of cost growth, schedule growth, and construction intensity.