Preliminary engineering cost-estimation strategy assessment for roadway projects

Preliminary engineering (PE) for a roadway project encompasses two efforts: planning to minimize the physical, social, and human environmental impacts of projects and engineering design to deliver the best alternative. State transportation agencies strive to manage these efforts efficiently, seeking to maximize the utilization of limited funding and workforce productivity. Managers need a feasible PE budget, considering both cost and time, early in project development. The results reported herein will provide engineers and managers with a comparative investigation evaluating different strategies for establishing a PE budget during the preconstruction phase of roadway project development. Cost data were obtained for 188 North Carolina roadway projects built between 1999 and 2009. An analysis of the North Carolina DOT data yielded an overall mean ratio of PE cost to estimated construction cost (the PE cost ratio) of 11.7%. The multiple linear regression model was used to develop prediction models to forecast the PE cost ratio of future roadway projects. It was found that while differing regression strategies could reduce prediction error, the improvement was small. In terms of simplicity, using the historical means applicable for widening projects (13.3%), rehabilitation/resurfacing projects (7.7%), and new location/interchange projects (16.5%) proved advantageous over regression modeling because a project manager would not have to estimate any project-specific values at the earliest stages of project development. The lowest of these historical means was significantly different than the two higher means (7.7% versus 13.3% and 16.5%); however, the difference between the two higher means (13.3% versus 16.5%) was not statistically significant. The study analyses also found a significant correlation between a project's PE cost ratio and its PE duration, suggesting that further investigation into PE duration of transportation projects is warranted.