 All of I-78 was completed by 1989.When the Interstate Highway System numbers were first assigned in 1957, the route was planned as I-80N.Prior to the late 1960s, I-78 was to be routed on the Lehigh Valley Thruway across to Phillipsburg, New Jersey, continuing the concurrency with US 22; however, because of heavy opposition by residents of Phillipsburg, the Pennsylvania Department of Transportation (PennDOT) and the New Jersey Department of Transportation opted to build the new southerly alignment on which I-78 is routed today.