Route 21 southbound in North Newark, along the Passaic River. This section features the southbound lanes passing directly over the northbound lanes. The downtown Newark skyline is visible in the distance on the left.|thumb|right Route 21 and CR 508 head along the west bank of the Passaic River, passing by the New Jersey Performing Arts Center. CR 508 splits from Route 21 by heading east on Bridge Street, crossing the Passaic River, and Route 21 continues north, passing by the former site of Bears & Eagles Riverfront Stadium. After passing under NJ Transit's Montclair-Boonton Line/Morris & Essex Lines and interchanging with I-280, the route intersects with Clay Street (CR 506 Spur). Past the intersection with 3rd Avenue, Route 21 becomes a six-lane freeway again. After about a quarter mile, the northbound side swings under the southbound side and the freeway becomes double-decker, passes by Mt. Pleasant Cemetery, and returns to single-decker configuration. It then interchanges with Chester Avenue and Riverside Avenue with a southbound exit and northbound entrance before passing over Norfolk Southern Railway's Newark Industrial Track line. Route 21 comes to a northbound exit and southbound entrance for Grafton Avenue and Mill Street; this interchange actually connects with the original McCarter Highway, a street that retains this name and acts as a service road to Route 21 for a few blocks in this area, near several industries. Route 21 briefly becomes a double-decker freeway again past the latter interchange and passes under Norfolk Southern Railway's Boonton Line, before crossing into Belleville at the Second River crossing. The freeway features a southbound exit for Mill Street and a northbound exit for Rutgers Street/Belleville Turnpike (Route 7 and CR 506) as it passes by houses on the left side of the freeway. Route 21 features an interchange with Main Street that has a southbound exit and an entrance in both directions. It enters Nutley where the freeway interchanges with County Route 646 (Park Avenue), continuing north through residential areas along the Passaic River.
Route 21 southbound in North Newark, along the Passaic River. This section features the southbound lanes passing directly over the northbound lanes. The downtown Newark skyline is visible in the distance on the left.|thumb|right Route 21 and CR 508 head along the west bank of the Passaic River, passing by the New Jersey Performing Arts Center. CR 508 splits from Route 21 by heading east on Bridge Street, crossing the Passaic River, and Route 21 continues north, passing by the former site of Bears & Eagles Riverfront Stadium. After passing under NJ Transit's Montclair-Boonton Line/Morris & Essex Lines and interchanging with I-280, the route intersects with Clay Street (CR 506 Spur). Past the intersection with 3rd Avenue, Route 21 becomes a six-lane freeway again After about a quarter mile the northbound side swings under the southbound side and the freeway becomes double-decker, passes by Mt. Pleasant Cemetery, and returns to single-decker configuration. It then interchanges with Chester Avenue and Riverside Avenue with a southbound exit and northbound entrance before passing over Norfolk Southern Railway's Newark Industrial Track line. Route 21 comes to a northbound exit and southbound entrance for Grafton Avenue and Mill Street; this interchange actually connects with the original McCarter Highway, a street that retains this name and acts as a service road to Route 21 for a few blocks in this area, near several industries. Route 21 briefly becomes a double-decker freeway again past the latter interchange and passes under Norfolk Southern Railway's Boonton Line, before crossing into Belleville at the Second River crossing. The freeway features a southbound exit for Mill Street and a northbound exit for Rutgers Street/Belleville Turnpike (Route 7 and CR 506) as it passes by houses on the left side of the freeway. Route 21 features an interchange with Main Street that has a southbound exit and an entrance in both directions It enters Nutley where the freeway interchanges with County Route 646 (Park Avenue), continuing north through residential areas along the Passaic River.