The route is 2.73 miles (4.39 km) long and runs between US 1 in Trenton and Lawrence Township.

in Trenton is now signed by the New Jersey Department of Transportation as part of US 1 Bus., despite not being officially recognized as such.

begins at a split from the median of the US 1 freeway in Trenton, having access to and from the south along US 1.

The road heads north as a four-lane divided highway before making a turn to the northwest.

[1] The route becomes four-lane undivided Strawberry Street and passes through residential areas.

[1][2] At the border of Lawrence Township and Trenton, the road enters the Brunswick Circle, where it junctions with northbound US 206 and CR 645.

[1] The road runs through residential and commercial areas and passes Colonial Lake, with a few intersections controlled by jughandles.

[1][2] Despite the official route beginning at US 1 near the Brunswick Circle, signage has US 1 Bus.

At the south end of Route 31, the one-way pair becomes Brunswick Avenue northbound and Martin Luther King Jr. Boulevard southbound, heading northeast.

The one-way pair continues to the Brunswick Circle, where the official US 1 Bus.

[9][10] In December 1952, the Trenton–Morrisville Toll Bridge and its approaches opened, which included the Trenton Freeway between the Delaware River and the Brunswick Circle.

was designated onto the former US 1 between the freeway's north end and the interchange at Strawberry Street.