Interstate 83 Exit 4 is an existing diamond configuration interchange with signals located at the ramp intersections with PA 851. Due to the growth of the Shrewsbury area, congestion is experienced at the interchange during peak periods, and traffic exiting I-83 northbound and southbound backs up onto I-83. Two options have been developed for the reconstruction of the interchange:
- A Tight Diamond Interchange configuration, similar to the existing configuration, but with two eastbound and two westbound lanes on PA 851 with dedicated left turn lanes onto northbound and southbound I-83 at the signalized ramp intersections.
- A Diverging Diamond Interchange configuration with two eastbound and two westbound lanes on PA 851 which utilizes signalized ramp intersections to cross traffic over to the left side of the roadway with a return to the right side within the interchange limits. This is to improve all traffic movements, particularly left turns, to and from I-83.
Both options include the reconstruction of the bridge that carries I-83 over PA 851 with a two-span structure that will accommodate the additional lanes on PA 851 and accommodate possible future widening of I-83. Also included is the lengthening of the I-83 northbound and southbound on and off interchange ramps.