=+factors. From about the mid-1990s to 2010, Kentucky’s annual average API and DPI were found to be closely related to the annual average crude oil price. Based on this, the authors suggested that crude oil price could be used to predict API and DPI (“Prices of Highway Resurfacing Projects in Economic Downturn: Lessons Learned and Strategies Forward,” J. Mgmnt. Engr., 2012, 391–397).