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.

From this interchange, Route 173 heads east on a two-lane, undivided road that parallels Interstate 78/U.S.

Route 22 to the south, immediately entering Greenwich Township and passing through farmland and some suburban residential developments.

[1] Route 173 crosses the Musconetcong River into Bloomsbury, Hunterdon County.

[1] The route enters Bethlehem Township and passes under Norfolk Southern's Central Running Track line, continuing east through farmland[1][2] The route parallels Norfolk Southern's Lehigh Line for a short distance, running farther to the north of Interstate 78/U.S.

[1][2] Past this intersection, Route 173 heads south and then east through the Musconetcong Mountains as a five-lane road with a center left-turn lane.

[1] Route 173 narrows back to a two-lane, undivided road and closely follows Interstate 78/U.S.

Route 22 and makes a left turn to merge onto eastbound Interstate 78/U.S.

[1] The route crosses into Clinton Township and it features ramps connecting to Interstate 78/U.S.

Construction of the portion of Interstate 78 built between Exit 11 (County Route 614) and Exit 13 in Union Township, completed in 1962, modified the alignment of U.S. Route 22 between these two points.

The westbound lanes of U.S. Route 22 were turned into a two-lane frontage road.