After crossing into New Jersey in Mercer County, US 1 continues on the Trenton Freeway through the city of Trenton and Lawrence as a four lane freeway. As the freeway ends, the four lane divided highway upgrades to six lanes after I-95/I-295 passing through the Penns Neck section of West Windsor Township. Through Penns Neck is a series of traffic signals. NJDOT is looking to revamp the highway through this area by removing traffic signals with grade separations. The highway enters Middlesex County through Plainsboro and South Brunswick. By Forrestal Village, the highway downgrades from 6 to 4 lanes until after Finnegans Lane in North Brunswick.