Interstate 129 is an auxiliary Interstate Highway which connects South Sioux City to Interstate 29 in Sioux City, Iowa. Opened in 1976, I-129 is a route, running in Nebraska. At, Interstate 129 is the shortest highway in the state of Iowa. All of the route's length is concurrent with US 20 and most of its length is concurrent with US 75. Interstate 129 is also one of only four auxiliary interstate highwaysto go into a state its parent route does not.
Route description
Interstate 129 begins along U.S. Route 20 on the western edge of South Sioux City, Nebraska, just west of exit 1, a cloverleaf interchange with U.S. Route 75 and U.S. Route 77. US 77 travels north through South Sioux City before ending at Interstate 29 in Sioux City while US 75 joins I-129 and US 20. One mile later, I-129 / US 20 / US 75 intersect Dakota Avenue at a partial cloverleaf interchange. U.S. Route 20 Business is designated along Dakota Avenue. East of Dakota Avenue, I-129 / US 20 / US 75 travels south of South Sioux City and passes through rolling farmland. For the rest of I-129's length, the two directions of I-129 / US 20 / US 75 traffic are separated by a Jersey barrier instead of a grassy median. The three routes cross the Missouri River and immediately intersect Interstate 29 at an interchange. Due to the minimum amount of space along the Missouri River banks, the I-29 interchange is a modified two-level cloverstack interchange. At I-29, US 20 and US 75 continue east around Sioux City and I-129 ends.
History
After the passage of the Federal-Aid Highway Act in 1968, the mileage which would eventually be manifested in over of interstate highway was allocated to the states. Iowa received the smallest allocation,, for the southern bypass of Sioux City. The proposed highway was planned to cost $22.5 million, which included $15 million for the Missouri River bridge. On the 1973 state highway map, the Iowa State Highway Commission showed the planned route on the state map for the first time. Interstate 129 was opened on November 22, 1976.
