On Highlighting the Need for Constructability Considerations When Evaluating Scope and Quantity Takeoffs for Estimates
Courses in undergraduate estimating emphasize quantity takeoffs. Usually, discussions of constructability decisions and their impacts on scope and cost are not covered in these courses. The need for students to have awareness of constructability impacts on projects costs has been identified as a shortcoming in construction management undergraduate education. Case studies and discussions have been cited as effective teaching tools. This paper discusses a case study derived from a construction project managed by the author that is used to illustrate the impact of constructability on a project’s cost in estimating classes taught by the author. Execution decisions made by the contractor and scope and costs resulting from them were included in the final bid. The case lends itself to treatment of constructability impacts on scope and cost in multiple ways, and also lends itself to treatment of other estimating and cost-related concepts useful in undergraduate construction management education.
Assessment of Spatial Correlation Patterns of Unit Price Bids and External Factors
The generalized linear modeling (GLM) approach overlooks the spatial correlation between the unit price bids and the geographical location of a project, leading to over- or underestimating the significance of explanatory variables. State departments of transportation (DOTs) often encounter over- or underestimation of their construction costs, which can cause cost overruns, inefficient budget allocation, and project delays or cancellation. The overarching objective of this study is to explain variation in the submitted unit price bids for asphalt line items used in highway projects. The study applies geographically weighted regression (GWR) analysis to explore spatial variations of relationships between submitted unit price bids and explanatory variables and to create a set of local models with the capability to describe variations in submitted unit price bids. The regression analysis of submitted unit prices for asphalt line items, drawn from in-highway pavement projects in the state of Georgia between 2008 and 2015, examines key variables, including the quantity of the bid item, the total contract price, the number of bids, the dollar value of a project, and the price index of asphalt cement. The results indicate significant spatial variation in the relationship between submitted unit price bid and the identified explanatory variables. Not only is GWR analysis capable of more accurately describing variation in submitted unit price bids, but it also provides a means of exploring the geographical variation of construction costs in a graphical manner.