Medary.com

Article in the Sioux Falls Argus Leader:

In 1956 the first portion of Interstate 29 was completed, but it wasn't until 1983 that the state opened the last 22 miles to make South Dakota only the sixth state to boast a border-to-border system.

For cities such as Sioux Falls, Watertown and Rapid City, it bolstered the economy and tourism.

"There is no better economic development tool than the interstate," Judith Payne, secretary of the South Dakota Department of Transportation, said Monday during a celebration of the system's 50th anniversary in Sioux Falls.

Almost all of the economic and population growth in South Dakota is within 20 or 30 miles of an Interstate highway.  Towns which were bypassed, like Huron and (to a lesser extent) Aberdeen, are struggling to survive.