[4] The complete (as originally planned) 24-mile (39 km) route between Portsmouth and Rochester opened on August 29, 1957, the same day that the Everett Turnpike was dedicated.

[4] In 1977, the New Hampshire House of Representatives approved funding to extend the Spaulding Turnpike by 12 miles (19 km) north through Milton.

Exit 2, a northbound-only exit/entrance which facilitated access to the Mall at Fox Run and adjacent businesses, was closed permanently on July 19, 2015.

US 4 leaves the turnpike at Exit 6, with the Dover barrier toll located about 700 metres (770 yd) to the north.

The reconstruction of Exit 6 into a full access diamond interchange between Dover and Durham was open to traffic on November 15, 2019.

Immediately north of Exit 16, the turnpike becomes a two-lane freeway and the speed limit drops to 55 mph (90 km/h).

The Spaulding Turnpike designation ends at Exit 18 near Union; NH 16 continues north as a two-lane freeway.

In November 2021, the New Hampshire Department of Transportation announced the installation of all-electronic tolling and collection of funds using E-ZPass transponders that are scanned by sensors for payment.

[13] Toll rates are determined by the class of vehicle (number of axles, single or dual rear tires).

The NHDOT currently offers discounted tolls for customers utilizing E-ZPass transponders registered with the agency.