Mackin performed preliminary engineering, environmental clearances, and final design for the interchange of U.S. Route 22 with State Route 66 near Delmont, Westmoreland County. The existing cloverleaf interchange was constructed nearly 50 years before and no longer complied with current design standards or criteria. The project also included widening and traffic improvements to Route 22 and Route 66.
Various conventional interchange configurations were considered for this project. In performing this study, it was found that no standard interchange designs would meet all of the strict criteria. When alternative design options were explored, Mackin determined that a Single Point Urban Interchange (SPUI) configuration would meet all geometric criteria, provide increased levels of traffic service, and meet all District conditions. This became the first interchange of this type constructed in the state.
