The Montour Trail website has instructions for the remaining bypasses. For this particular one, the say:
"Gill Hall Road to Large
Mile 44 40° 17.574? N, 79° 54.675? W
In this section the MTC does not own trail right-of-way, requiring this 3.4 mile on-road section.
Eastbound: Cross Gill Hall and continue on Peter’s Creek Road for 2.5 miles to Cherry Street. Cherry becomes First Street. Follow First Street 0.1 mile, turn right onto Oak Road (marked as Maple), continue 0.5 mile on Oak (past the foundation of the recently demolished Large Hotel on the curve) to PA Rt. 51. Cross Rt. 51 at the light and walk your bike across the grassy strip on the east side of the road in front of the funeral home. Stay on the grassy strip on the east (left!) side of the road. Do not go onto Rt. 51 because it is a four-lane road with heavy traffic and no shoulders. Go past the brick buildings and the sign marked Jefferson Technology Center and turn left onto Peters Creek Road (before Piney Fork Creek). Follow this road past the Park and Ride lot (under Route 43). The trail starts at the extreme back end of the lot near the “No Outlet” sign next to the creek.
Westbound: The trail terminates into the Park and Ride lot under Rt. 43. Proceed on Peters Creek Road through the lot 0.3 miles then turn right into parking lot for Jefferson Technology Center adjacent to Rt. 51. (Do not leave the parking lot for Rt. 51 because it is a four-lane road with heavy traffic and no shoulders, and is not safe for biking.) At the end of the parking lot stay on the grassy strip on the east (right) side of the road. Cross Rt. 51 at the traffic light for Old Clairton Road and nce across, immediately turn left onto Oak Road Go past the foundation of the recently demolished Large Hotel on your right and follow Oak for a total of 0.5 miles. Turn left on First Street and go 0.1 mile; then turn left again after a 90-degree bend in the road. Follow public paved road (Peters Creek Road) for 2.5 miles to Gill Hall Road (Montour Trail signs posted along the road). The trail continues straight ahead on its own right of way on the left side of Piney Fork Rd."
Not sure if that answers you question in full, but I thought I'd quote it here in case you weren't aware of the MTC position on the bypass.
2017-05-31 03:55:18