 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'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 Route 7 and County Route 506 (Rutgers Street/Belleville Turnpike) as it passes by houses on the left side of the freeway.