Impact of Design Cost on Project Performance of Design-Bid-Build Road Projects

The vast majority of highway and street projects in the United States are procured and constructed by state or local governments using the design-bid-build (DBB) project delivery method. In the DBB method, the contractors build the project according to the detailed design and specifications prepared by the engineers. Using the DBB method, the quality of design has an impact on the construction performance. To date, only a few studies have measured the effect of design cost on the project performance of the road projects. In order to determine the impact of design cost on construction cost and schedule performance, this paper analyzes a sample of 47 Clark County public road projects of Nevada and 17 road projects of the Texas Department of Transportation (TxDOT). The sample includes projects completed between 1991 and 2009, and cost more than $3.43billion in construction value, converted to a 2010 base cost. Besides determining the impact of design cost on the cost and schedule growth of the road projects, this study also determines a correlation between the design cost percentage and the final project cost of the projects. The analysis showed a significant negative correlation between the design cost percentage and the total cost growth of the project. In addition, the design cost percentage was found to have a strong negative correlation with the final project cost for this sample. The t-test showed that the design cost percentage of road projects that have total cost growth less than or equal to zero was significantly higher than that for road projects that have a total cost growth higher than zero.