This study evaluates both the transportation efficiency benefits and economic development impacts of the completed portions of the Appalachian Development Highway System (ADHS). The study focuses on 12 of the 26 ADHS highway corridors that were largely completed, totaling 1,400 miles of the system. A primary objective of the study is to measure, in retrospect, the extent to which the completed portions of the ADHS have contributed to the economic well-being of Appalachia. Two major effects are estimated using transportation data and a state-of-the-art regional economic model: travel efficiency benefits due to reduced travel time, lower vehicle operating costs, and the reduced number of accidents; economic development impacts on the Region due to the enhanced competitive position of industry in the Region, increased roadside business, and increased tourism. The economic model used for the study was developed by Regional Economic Models Inc., of Amherst, Massachusetts, which estimated the employment, wages, value-added, and population increases attributable to the ADHS in the 165-county study region.