Never actually signed as I-178 in the field, initial plans for the route originated in a 1954 plan for the Allentown Spur Route. The limited access highway was proposed from a new interchange with U.S. 22, east of the Lehigh River to 3rd and Hamilton Streets, west of the river in Allentown.1 Plans for the route were included in an improvement plan drafted by the Lehigh Valley Planning Commission in 1968.2
Lack of funding for the $35 million project in 1976 halted plans for the route.1 An alternate proposal arose in the mid-1980s by Allentown officials.2 Named American Parkway and following an abandoned Conrail line right of way, the new at-grade road was envisioned to run north from Hamilton and Front Streets, across the Lehigh River to Airport Road.1 Construction was proposed to commence in 1990.2
Work on American Parkway did not start until December 2012 due to land rights issues, funding shortages and delays in design and environmental studies.2 The initial stretch opened to traffic connected Dauphin Street and Airport Road. An eastern extension to Nelson Street was also constructed.3 The bridge across the Lehigh River was built last, having opened on November 24, 2015 after a ribbon cutting ceremony held at 11 that morning. The span was previously planned for completion in December 2014, but fractured rock discovered beneath the river bed led to delays on the $36 million project.2
More information on decommissioned Interstate 178 available at Pennsylvania Highways: Pennsylvania’s Dearly Departed Interstates.