U.S. Route 1/9 (US 1/9 or US 1-9) is the 31.0-mile-long (49.9 km) concurrency of US 1 and US 9 from their junction in Woodbridge in Middlesex County, New Jersey, north to New York City.

The route is a multilane road with some freeway portions that runs through urbanized areas of North Jersey adjacent to New York City.

[5][6] The current alignment of US 1/9 south of Elizabeth was planned as Route 1 in 1916; this road was extended to the Holland Tunnel in Jersey City in 1922.

When the U.S. Highway System was created in 1926, US 1 and US 9 were marked concurrent through northern New Jersey between Rahway on the current alignments of Route 27 and Truck US 1/9.

[1] US 1 comes from the southwest, where it serves the state capital of Trenton, along with New Brunswick and Edison; while US 9 comes from the south, where it serves the Jersey Shore region, along with the suburban communities of Freehold Township and Old Bridge; a short distance to the north of an interchange with the New Jersey Turnpike (I-95) and the Garden State Parkway.

[7][8] The combined US 1/9 runs northeast through business areas as a six-lane divided highway, coming to a partial cloverleaf interchange with Route 35 a short distance after the merge.

Following the intersection with South Stiles Street (CR 615), the road enters more urbanized areas of homes and businesses.

[1] Past this interchange, US 1/9 continues into Elizabeth, where it intersects with South Elmora Avenue/Bayway (Route 439) at the Bayway Circle, which has been modified to allow US 1/9 to run straight through.

The road continues north through urban neighborhoods as Spring Street, passing under Conrail Shared Assets Operations' Elizabeth Industrial Track line.

[1][9] Past the crossing of I-78, US 1/9 continues north, with the lanes splitting as it passes over the Conrail Shared Assets Operations' Greenville Running Track, Lehigh Line, and Newark and Passaic Industrial Track at Oak Island Yard before coming to a northbound exit and southbound entrance with Delancy and South streets.

[1][9] Following this interchange, the directions of US 1/9 rejoin as the freeway continues northeast, with Conrail Shared Assets Operations' Passaic and Harsimus Line running closely parallel to the northwest of the road.

The local–express lane configuration of US 1/9 ends at an interchange with Truck US 1/9 and Raymond Boulevard that provides access to the New Jersey Turnpike (I-95).

Here, US 1/9 head north on four-lane divided surface road called Tonnele Avenue,[1] named for local landowner and politician John Tonnelé.

[1] From this point, US 1/9 continues north-northeast, crossing NJ Transit's Hudson–Bergen Light Rail near the line's northern terminus at the Tonnelle Avenue Station.

Shortly after entering Fairview, the route passes over the New York, Susquehanna and Western Railway's Edgewater Branch line, where it is briefly a divided highway.

US 1/9/US 46 continue into Fort Lee, where it has access to a couple commercial areas before encountering the northern terminus of Route 63 at a westbound exit and eastbound entrance.

From here, the highway becomes a surface road that continues past more businesses and homes, angling northeast as it comes to an exit for Main Street (CR 56).

[25][26] As part of construction of the New Jersey Turnpike, a new interchange was built to connect to the road, this replaced the existing turn circle in the area, which had grown functionally obsolete with increased traffic.

From 1958 to 1964, the portion of road near and over the George Washington Bridge, which were shared with US 46 on the New Jersey side, were rebuilt into a freeway that became a part of I-95.