 Much of I-78 west of Allentown predates the Interstate Highway System as a freeway upgrade of U.S. Route 22 (US 22), which runs concurrently with I-78 between Bethel Township and Upper Macungie Township.The Interstate, originally planned as I-80N, was supposed to continue its concurrency with US 22 to the New Jersey state line, but was realigned to the south due to local opposition.Two auxiliary routes, I-178 and I-378, were also planned; I-178 was never built while I-378 became Pennsylvania Route 378 (PA 378) as it no longer connected to I-78.