I-476 comes to the Mid-County Interchange, where it enters the Pennsylvania Turnpike system and has a mainline toll plaza before coming to an interchange with I-276 (which follows the mainline of the Pennsylvania Turnpike), heading north from here as the six-lane Northeast Extension of the Pennsylvania Turnpike. The route continues through the Philadelphia suburbs, passing over CSX's Stony Creek Branch rail line, and reaches an interchange with PA 63 west of Lansdale that serves the North Penn Valley region. Past this interchange, the route enters a more rural setting of woods and farms, narrowing to four lanes before crossing into Bucks County and coming to an interchange with PA 663 west of Quakertown. The Northeast Extension continues northwest into Lehigh County, part of the Lehigh Valley metropolitan area, past the PA 663 interchange. Here, the road heads into more developed areas and passes over Norfolk Southern's Reading Line. The route has ramps to the dual-access Allentown Service Plaza in Upper Macungie Township, and, just north of it, I-476 reaches an interchange with US 22 (Lehigh Valley Thruway) west of Allentown, which offers an indirect connection to I-78 and PA 309. North of Allentown, the route crosses under Norfolk Southern's C&F Secondary rail line and runs through farmland with some development. The road passes under Blue Mountain in the Lehigh Tunnel and enters Carbon County in the Pocono Mountains region. Here, I-476 crosses over the Lehigh River and Norfolk Southern's Lehigh Line before it has an interchange with US 209 east of Lehighton. Continuing through mountainous areas, the route has ramps to the dual-access Hickory Run Service Plaza prior to coming to a diamond interchange with PA 903. Past here, I-476 cuts through Hickory Run State Park before reaching an interchange with PA 940 providing a connection to I-80 just to the north of the state park. The route continues through mountainous terrain, heading into Luzerne County at a crossing of the Lehigh River and coming to an interchange with PA 115 in Bear Creek that provides access to nearby Wilkes-Barre. The route comes to a mainline toll plaza near Pittston that marks the northern end of the distance-based toll system along the Northeast Extension. A short distance later, an interchange with PA 315 provides indirect access to I-81 and Scranton. Past this interchange, I-476 crosses under a Luzerne and Susquehanna Railway line before it enters Lackawanna County. Here, the route