Regional Modeling of the Variability of Riprap Prices in Alabama: A Riprap Location Cost Index

Riprap is widely used by state departments of transportation (DOTs) for erosion control and slope stabilization purposes. Even though DOTs seem to be satisfied with the ability of riprap to fulfill its intended purpose, its cost-effectiveness has been increasingly questioned, mainly in job sites where riprap is not locally or nearby available resulting in increased costs due to longer haul distances. This is an issue in some parts of Alabama where soils are not suitable for the production of riprap. Before considering alternative technologies or materials, the Alabama Department of Transportation (ALDOT) must first understand how riprap prices vary across the state to facilitate the identification of regions where substitutes to riprap could offer better cost-effectiveness. This paper models and quantifies this price variability in the form of a riprap location cost index (RLCI). The study identified statistically significant differences in riprap prices across four geographic regions in Alabama: north, central, south-west, and south-east. These are the regions upon which the RLCI was built. The development of the RLCI involved the use of advanced data collection, cleaning, and processing techniques to analyze historical bid data from projects awarded by ALDOT between 2006 and 2016.