PA 378 was originally designated in the 1928 numbering as an alignment of PA 12, a route crossing through Northampton and Monroe Counties. As the area grew in the 1950s, several proposals to connect the city with the newly built Lehigh Valley Thruway to the north were reviewed.
The current alignment of PA 378 was first constructed from West Broad Street in Bethlehem to the current interchange with the Lehigh Valley Thruway. Construction began in 1966 with the completed expressway opening to traffic in 1968. This highway was designated as Interstate 378, (I-378). However, in 1970, the plan to connect the Lehigh Valley Thruway (I-78, now route 22) was changed because of the resistance of Philipsburg, NJ residents to have the thruway travel through residential areas. At this point, I-378 was decommissioned and replaced with the alignment of PA 378 the following year.
Since completion, PA 378 has undergone little major change, but the highway has undergone several rehabilitations. The Hill to Hill Bridge received a minor fire during reconstruction of the bridge, when a piece of equipment had its motor catch fire on April 13, 2009, when the bridge was undergoing re-painting. The bridge repainting was completed on May 15, 2009, after the closing of a bridge and was re-opened later due to rainfall in the area.
On September 23, 2009, the Pennsylvania Department of Transportation announced plans and designs for an upgrade and redesign of PA 378 through Bethlehem at its interchange with West Third Street, although this met public criticism. Part of the project, construction of a new ramp from Wyandotte Street to West Third Street, was completed in September 2011. Completion of the widening of West Third Street and PA 412 was completed later in 2011. The $5.1 million project will also include a widening of PA 412 between Exit 67 on I-78 and Daly Avenue in Bethlehem to two lanes in each direction. On November 21, 2009, the project was given funding from the American Recovery and Reinvestment Act of 2009 signed by President Barack Obama in 2009. The Pennsylvania Department of Transportation received $1 billion worth of funding from the act.
For more information about the history of both I-378 and I-78, visit these pages:
Source: Source: Wikipedia, Interstate-Guide.com