It runs from the Massachusetts border north to Rye , then turns toward downtown Portsmouth .
New Hampshire Route 1A is an 18.32 - mile ( 29.48 km ) auxiliary of US 1 which runs along the Atlantic coastline .
US runs from the Massachusetts border north to Rye , then turns toward downtown Portsmouth .
New Hampshire Route 1A is an 18.32 - mile ( 29.48 km ) auxiliary of US 1 which runs along the Atlantic coastline .