Interstate 378 Pennsylvania


Interstate 378 was the original designation for the freeway spurring southward from U.S. 22 (Lehigh Valley Thruway) near Allentown-Bethlehem-Easton Airport to Downtown Bethlehem. The short spur winds southeast to end at the Hill to Hill Bridge across the Lehigh River. Sequential exit numbers used along the route increase as one travels southward.


The Interstate 378 freeway was constructed between 1966 and 1968.1 The route was signed as I-378 until Interstate 78 shifted southward to a new alignment. This led the AASHTO approval of eliminating I-378, and the adjacent Allentown Spur (I-178), at their meeting on June 30, 1970. Today, the Lehigh Valley Thruway is solely signed as U.S. 22 and former I-378 now represents the northern third of Pennsylvania 378, a 9.55-mile route stretching south to Pennsylvania 309 in Upper Saucon Township.

Interstate 378 was also once proposed to extend south across the Lehigh River to an end at an interchange with a planned freeway: Constitution Drive on the west and South Side Spur on the east. The South Side Spur was proposed to go east and south to Interstate 78 and may have become part of Interstate 378.

Southern Terminus - Downtown Bethlehem, Pennsylvania
Perspective from Pennsylvania 378 south
Looking south on Pennsylvania 378 (former Interstate 378 from 1968 to 1971), the final exit is Exit 3, West North Street, which provides access to the Center City of Bethlehem. The freeway ends in about a half-mile (note the expressway ends sign on the overhead sign bridge). Photo taken 09/01/05.
The speed limit drops to 40 miles per hour on the freeway. Note the older standards used on this freeway, including a limited shoulder, limited sight distance, and curves. The freeway is dropping a bit toward the Lehigh River. Photo taken 09/01/05.
The Lehigh River bridge comes into view as Pennsylvania 378 rounds the last corner. All four lanes cross the bridge, only to culminate at a traffic signal. Turn left on Pennsylvania 412 (Third Street) to Lehigh University. Photo taken 09/01/05.
Preparing to cross the Lehigh River on this truss bridge, the former Interstate highway came to an end here. The bridge was not part of the former Interstate, and there is no median or barrier separating the two directions of traffic. On the south side of the bridge, Pennsylvania 378 meets Pennsylvania 412 (Third Street) at a traffic signal, with Polaski Park serving as the green space between the directions of traffic. Pennsylvania 378 will continue south as Wyandotte Street. Photo taken 09/01/05.
This dual truss bridge carries Pennsylvania 378/Bridge Street over the Lehigh River. On the south side of this bridge is the signalized intersection with Pennsylvania 412, which travels east and then south through Bethlehem, ultimately terminating at Pennsylvania 611 (Old U.S. 611) near Nockamixon State Park. Photo taken 09/01/05.
A pair of guide signs are mounted on the front of the second overhead truss section of this dual truss bridge. The left lane connects to Pennsylvania 412/Third Street, while the both lanes continue south along Pennsylvania 378/Wyandotte Street. Photo taken 09/01/05.
After the Lehigh River bridge, Pennsylvania 378 meets Pennsylvania 412/Third Street at this signalized intersection. Photo taken 09/01/05.
Perspective from Pennsylvania 378 north
Northbound Pennsylvania 378/Bridge Street meets Pennsylvania 412/Third Street in Bethlehem. This marks the northern terminus of Pennsylvania 412. Pennsylvania 378 prepares to cross the Lehigh River on this dual truss bridge, then becomes a freeway (joining former Interstate 378) on the north bank. Photo taken 09/01/05.
The dual truss, locally known as the steel bridge, carries four lanes of traffic over the Lehigh River. Downtown Bethlehem sits on the north bank of the river; Lehigh University sits on the south bank. Photo taken 09/01/05.
Between the two trusses visible to drivers on Pennsylvania 378 north, both motorist and pedestrian scale lighting is available for safety on the bridge at night and during inclement weather. Note the older style of concrete guardrail along the pedestrian walkway. Photo taken 09/01/05.
A pair of guide signs are mounted on the second visible truss on the Lehigh River bridge. Northbound Pennsylvania 378 will transition to freeway standards after the Main Street exit. The off-ramp actually carries Bridge Street into downtown Bethlehem; it intersects with Main Street at its eastern end. Photo taken 09/01/05.
Northbound Pennsylvania 378 reaches the Main Street off-ramp. From here, Pennsylvania 378 follows former Interstate 378 (signed from 1968 through 1971) north to U.S. 22/Lehigh Valley Thruway. Photo taken 09/01/05.
A restoration area and greenbelt lines Pennsylvania 378 as it begins the freeway journey north to U.S. 22. Photo taken 09/01/05.
This is the first northbound Pennsylvania 378 reassurance shield since the freeway began. For a very brief time, this freeway was signed as Interstate 378. Photo taken 09/01/05.
The next exit along northbound Pennsylvania 378 is Exits 2E-W, Eighth Avenue. The first exit connects to northbound Eighth Avenue (Exit 2E), followed by the ramp to southbound (Exit 2W). Photo taken 09/01/05.
Northern Terminus - U.S. 22 - northern Bethlehem, Pennsylvania
Perspective from Pennsylvania 378 north
About midway along its freeway portion, northbound Pennsylvania 378 (former Interstate 378, 1968-1971) approaches its junction with Eighth Street (Exits 2E-W). Photo taken 09/01/05.
Northbound Pennsylvania 378 (former Interstate 378) reaches Exit 2E, Eighth Street north. The next exit is a loop ramp that connects to Exit 2W, Eighth Street south. Photo taken 09/01/05.
With a guide sign mostly obscured by brush, northbound Pennsylvania 378 (former Interstate 378) reaches Exit 2W, Eighth Street south. The next exit is the junction with U.S. 22/Lehigh Valley Thruway, several miles northwest of here. Photo taken 09/01/05.
Newer reflective signs for U.S. 22 grace the first lane allocation signage for the connection to the Lehigh Valley Thruway on northbound Pennsylvania 378. Photo taken 09/01/05.
Use U.S. 22 west to the Lehigh Valley International Airport (left lane on northbound Pennsylvania 378). Photo taken 09/01/05.
To Schoenersville Road, use U.S. 22 east, then follow the signs on the collector distributor lanes. Unlike Exit 1 on southbound, there is no direct ramp to Schoenersville Road or Catasauqua Road on northbound. Photo taken 09/01/05.
Northbound Pennsylvania 378 (former Interstate 378) comes to an end at this point, where the right lane transitions onto eastbound U.S. 22 (former Interstate 78) to Easton and the left lane transitions onto westbound U.S. 22 to Allentown. This marks the northern terminus of Pennsylvania 378 and the end of the old Interstate highway. Photo taken 09/01/05.
Perspective from U.S. 22/Lehigh Valley Thruway east
This mileage sign is the first indication of the pending junction with Pennsylvania 378 south to Bethlehem. Pennsylvania 378 was formerly known as Interstate 378 when Interstate 78 was planned to follow U.S. 22 along the Lehigh Valley Thruway. Since Interstate 78 now bypasses the valley to the south, Interstate 378 was orphaned and renumbered as a state route. Photo taken 09/01/05.
After traffic merges back onto eastbound U.S. 22 from Pennsylvania 987/Airport Road, the new lane becomes the exit only connection to Pennsylvania 378 south to Bethlehem. Photo taken 09/01/05.
Use Pennsylvania 378 south to downtown Bethlehem and Lehigh University. The route is freeway south to the Lehigh River bridge; the university is located on the south bank of the river along Pennsylvania 412/Third Street east. Photo taken 09/01/05.
Eastbound U.S. 22/Lehigh Valley Thruway (Former Interstate 78) reaches the ramp to southbound Pennsylvania 378 (former Interstate 378). Photo taken 09/01/05.
Now on the collector distributor lanes for the trumpet interchange that serves Pennsylvania 378 as well as the connection to Schoenersville Road, the first ramp connects to Pennsylvania 378. The collector distributor lane continues east to Schoenersville Road, then rejoins eastbound U.S. 22. Photo taken 09/01/05.
Perspective from Pennsylvania 378 south
The first exit along southbound Pennsylvania 378 is Exit 1, Catasauqua Road to Schoenersville Road. The exit numbers on this short freeway are sequential, not mileage-based. The signs along this stretch mostly date back to the late 1960s when the freeway was built. Photo taken 09/01/05.
Southbound Pennsylvania 378 reaches Exit 1, Catasauqua Road (east to Schoenersville Road, which parallels Pennsylvania 378 to the east). The next exit is Exit 2, 8th Avenue (one and one-half miles). Note that the sequential exit numbers increase as the freeway travels farther south. Photo taken 09/01/05.
Continuing south, this is the one-mile advance sign for 8th Avenue. This is almost the midpoint of the short freeway. Photo taken 09/01/05.
Pennsylvania 378 briefly turns east to interchange with Exit 2, 8th Avenue. The last exit on southbound is Exit 3, West North Street/Center City. Photo taken 09/01/05.


  1. Pennsylvania Highways:  Pennsylvania's Decommissioned Interstates.

Page Updated May 26, 2015.