 Route 21 heads north from the Newark Airport Interchange with U.S. Route 1/9 and U.S. Route 22 in Newark near the Newark Liberty International Airport on the six-lane, divided McCarter Highway.This portion of Route 21 serves to connect Newark Liberty with downtown Newark.The route interchanges with Interstate 78 and then crosses over Conrail Shared Assets Operations' Greenville Running Track, Lehigh Line, and Passaic and Harsimus Line and then Amtrak's Northeast Corridor rail line on a viaduct, coming to an interchange with Broad Street that provides access to Frelinghuysen Ave./Route 27.