(Maine State Route 113 does cross into New Hampshire near NH 113, but remains completely under MaineDOT maintenance.)

The exact routing differs depending on which direction one is traveling, due to the one-way streets it traverses in the downtown area.

It is the only state route to pass through Rollinsford and runs in the south-central part of town for about 2.5 miles (4.0 km).

NH 4 (and State Route 4 in Maine by extension) was originally intended to be a part of US 4, hence its number.

US 4 only travels through a small section of southern Dover (mostly along the Spaulding Turnpike) which is several miles from downtown, meaning it was unlikely that the two highways would be easily confused.