New Hampshire State Route 16 is a north-south highway that runs briefly in Northern Rockingham County. It runs along the Spaulding Turnpike. NH St Rt 16 passes through the following town in Rockingham County. Portsmouth NH St Rt 16 is multi-plexed in Rockingham County. U.S. Rt. 4, at Portsmouth. Spaulding Turnpike, at Portmouth. NH St Rt 16 intersects the following highways in Rockingham County. BY-PASS U.S. Rt. 1, at Portsmouth.