Comprehensive Design of Interchanges and Connector Roads in Rural Areas: Kentucky Case Study

The main objective of this study is to accommodate the increasing vehicular traffic through Simpson County, Kentucky, with emphasis on truck traffic. The study involved thoroughly designing a new interchange along Interstate-65 (I-65) and creating a connector road between the interchange and the major road arterial, US-31W. All engineering specifications were followed per the American Association of State Highway and Transportation Officials (AASHTO) “Greenbook” and the Kentucky Transportation Cabinet (KYTC) design manual. A series of comprehensive analyses were performed using numerous software, including AutoCAD, OpenRoads Designer (ORD), Highway Capacity Plus (HCS+), ProjectWise, and crash information website. Each software provided unique capabilities to aid in the full roadway design. Examples of the analyses performed included: earthwork quantities estimation (either cut or fill), vertical and horizontal alignment design, level-of-service (LOS) analysis, crash and traffic safety investigation, and material cost calculations (for pavement design and construction). The benefit-to-cost (B/C) ratio selection method was then applied to assess the different design alternatives.

The design revealed that the diamond interchange was the optimal interchange type in the rural study area of Simpson County, Kentucky. The total study cost was estimated to be roughly $9.5 million. From the B/C ratio analysis, it was found that it would take 3.5 years to benefit from the proposed interchange construction (right after opening the interchange to the public) in reducing fatal-related crashes and 3.16 years to benefit in reducing total crashes. This study provides useful insights and guidance for appropriately selecting and designing new interchanges and connector roads in rural areas, which can be easily transferred to other rural states in the U.S.