US 16 formerly ran all the way across the state, to the
Minnesota state line east of
Sioux Falls. It entered the state on the current routing of
US 14/
I-90 (the current routing is former US 216) and followed the US 14 routing to Rapid City. It joined US 216 in Rapid City and continued east into
Box Elder. "Highway 14-16", as it was known, was a divided highway through most of Box Elder before returning to a two-lane road. (This road is still in use today, and still referred to as "14-16".) US 16 traveled east to
New Underwood, then continued through the foothills to
Wasta. The highway ran north of Wasta, across the
Cheyenne River, then ran southeast to
Wall. In Wall, an alternate route of US 16 (present day
SD 240) split from the highway and headed south, through the Badlands National Monument (now
Badlands National Park). US 14 and US 16 split south of
Philip, with US 14 traveling due east and US 16 continuing south (following present-day
SD 73 to its intersection with the eastern end of US 16 Alternate. From there, US 16 traveled due east, on the present-day routing of
South Dakota Highway 248 (
SD 248). The highway followed this routing through
Kadoka,
Murdo, and
Vivian, where it intersected
US 83. The highway continued east to
Reliance, where present-day SD 248 ends. US 16 then returned to the current routing of I-90 and followed this routing to
Oacoma, where it followed the current
I-90 Business to a bridge over the
Missouri River into
Chamberlain. East of Chamberlain, US 16 followed present day Old Airport Road to East King Street, then turned onto 249th Street just north of where I-90 now lies. It followed 249th Street to
Pukwana, present-day 350th Avenue to an intersection with
SD 47 (now
SD 50), 251st Street to
Kimball, and 252nd Street to
White Lake. US 16 then followed present-day County Road 34 (also named Old Highway 16) to
Mount Vernon and present-day 254th Street to
Mitchell. It then followed what is now
SD 38 east to 421st Avenue, 421st Avenue to
Alexandria,
SD 262 to
Bridgewater, and
SD 42 to
Sioux Falls. The highway followed Minnesota Avenue (
SD 115), 6th Street, Sycamore Avenue, Madison Street, and Splitrock Boulevard (
SD 11) to
Brandon. It then followed present-day Aspen Boulevard (formerly
South Dakota Highway 264, or
SD 264) from Brandon east to the
Minnesota state line north of
Valley Springs. ==Major intersections==