Comparing Cost Performance of Project Delivery Methods Using Quantifiable RFIs: Cases in California Heavy Civil Construction Projects

The objective of this research is to present the comparative analysis results for cost performance of the design–build and design–bid–build methods using quantifiable request for information data resulting in contract changer order or notice of design change to help both owners and contractors estimate inherent risk and additional costs. Quantifiable request for information data are collected from real heavy civil construction projects based on the reasons and costs. Statistical analysis using unbalanced t test, hypothesis tests, analysis of variance, and multiple comparisons with the best are conducted for comparison metrics such as mean costs of change orders triggered by requests for information for eight work elements and three main reasons, such as design, material, and craftsman. The results of statistical analysis indicated that the cost growths of the design–build projects and the design–bid–build projects are 0.77 and 11.3%, respectively, while the average cost per request for information of the design–build projects is 94.2% lower than that of the design–bid–build projects. The results showed the concurrence with the merits of change order metric. The results not only coincide with the existing body of knowledge on the cost performance of the project delivery methods, but also contribute to the change order research by a comparison between the design–build and design–bid–build projects.