Route 172 is a short state highway in New Brunswick, New Jersey, United States. The designation runs along the southernmost leg of George Street, which is county and city-maintained the rest of the way. Route 172 is 0.81 miles (1.30 km) long, serving as a connector from an interchange with New Jersey Route 18 to an intersection with County Route 527 and Middlesex County Route 672. The highway was assigned in the 1950s, when nearby Route 18 was realigned onto a new freeway over Burnet Street in New Brunswick. Route 172 underwent a major upgrade during the reconstruction of Route 18, including a roundabout at an intersection with Middlesex County Route 617, and a brand-new interchange with the local lanes of Route 18.

Route 172 begins at an interchange with New Jersey Route 18 in New Brunswick. The highway heads northward and passes through the Douglass Campus of Rutgers University. Route 172 then intersects with a local road, which serves the purposes of the university. The highway then progresses towards Middlesex County Route 617 (Ryders Lane), which heads northward from a roundabout with NJ 172. NJ 172 then turns to the west along George Street.

After the roundabout, Route 172 ducks down under a pedestrian overpass in the campus, heading along a university bus route. The highway intersects with Nichol Avenue, which terminates at the intersection. NJ 172 then continues down into New Brunswick. There, the highway intersects with Bishop Street, and terminates at an intersection with Commercial Avenue and County Route 527 continues along George Street, the right-of-way.

The interchange of Route 18 and Route 172 in New Brunswick

Route 172 originated as alignment of New Jersey State Highway Route S-28, which was assigned in the 1927 state highway renumbering. In the 1953 renumbering, State Highway Route S-28 was reassigned as New Jersey Route 18. However, just a few years after the designation of NJ 18 in New Brunswick along George Street, construction of a bypass around New Brunswick began. The highway was constructed along Burnet Street, which became state-maintained by the State Highway Department. The route was completed to NJ 27, and NJ 18 was moved onto that alignment. The former alignment of NJ 18 remained state-maintained up to the intersection with Commercial Avenue, which was redesignated as NJ 172.

When the New Jersey Department of Transportation started construction on upgrading the bypass, the fly-over ramp and on-ramp to and from NJ 172 were torn down for construction of a new interchange along a new local/express format. The overpass was closed on October 12, 2007 to begin the construction. The bridge was built in the 1950s and was replaced in 2008. On January 2, 2009, the new exit ramp for NJ 18 to NJ 172 was reopened to traffic.

The entire route is in New Brunswick, Middlesex County.