This highway forms one of the two main surface transportation links between the two provinces.

The following highways form the original route of US 23:

In the national forest, the highway forms a six mile (10 km) concurrency with Route 49.

Together, these three highways form a busy, limited-access multiplex through the city of Pittsburgh.

The major highways in province form a road network connecting all the counties.

There, the three highways form the southern terminus of SH-127.

Secondary highways in Ontario rarely ever form a concurrency, even with their own kind.

The highway also forms the boundary of Huntington State Park.

The highway forms a concurrency with US 79 briefly north before turning east then south.

The highway forms a southern border to the Elgin street grid.