Two auxiliary routes, Interstate 178 (I-178) and I-378, were also planned as spurs into Allentown and Bethlehem respectively, but I-178 was never built and I-378 became Pennsylvania Route 378 (PA 378) since it no longer connected to I-78.
Interstate 178 and Interstate 378 were both planned as spurs into Allentown and Bethlehem, but Interstate 178 was not constructed while Interstate 378 became Pennsylvania Route 378 (PA 378) due to its lack of connection with I-78.