Route 173 is a state highway in New Jersey, United States that is a designation for an old section of U.S. Route 22 (US 22). The route runs 14.62 mi (23.53 km) from Interstate 78 (I-78) and US 22 in Pohatcong Township, Warren County to County Route 626 in Clinton Township, Hunterdon County, just east of an interchange with Route 31. Route 173 parallels I-78 and US 22 for its entire length through rural areas of Warren and Hunterdon counties, passing through the towns of Bloomsbury and Clinton along the way. At one point just to the west of Clinton, Route 173 runs concurrent with I-78 and US 22.

U.S. Route 22 (US 22) is a United States Numbered Highway stretching from Cincinnati, Ohio, in the west to Newark, New Jersey, in the east. In New Jersey, the route runs for 60.53 miles (97.41 km) from the Easton–Phillipsburg Toll Bridge over the Delaware River in Phillipsburg, Warren County, to Interstate 78 (I-78), US 1/9, and Route 21 at the Newark Airport Interchange in Newark, Essex County. The road first heads through the Phillipsburg–Alpha area as an arterial road before running concurrent with I-78 through mountainous and agricultural sections of western New Jersey between Alpha and east of Clinton in Hunterdon County. For the remainder of the route, US 22 runs to the south of I-78 through mostly suburban areas as a four- to six-lane arterial road, passing through Hunterdon, Somerset, Union, and Essex counties. Along this portion, it intersects US 202 and US 206 in Somerville, I-287 in Bridgewater Township, and the Garden State Parkway in Union.