Interstate 129 (I-129) is an auxiliary Interstate Highway which connects South Sioux City to

I-29 Interstate 29 (I-29) is an Interstate Highway in the Midwestern United States. I-29 runs from Kansas City, Missouri, at a junction with I-35 and I-70, to the Canada–US border near Pembina, North Dakota, where it connects with Manitoba ...

Sioux City, Iowa Sioux City () is a city in Woodbury and Plymouth counties in the northwestern part of the U.S. state of Iowa. The population was 85,797 in the 2020 census, making it the fourth-largest city in Iowa. The bulk of the city is in Woodbury County ...

. Opened in 1976, I-129 is a route, running in

Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the sout ...

. At , I-129 is the shortest highway in the state of Iowa. All of the route's length is concurrent with U.S. Route 20 (US 20) and most of its length is concurrent with US 75. I-129 is also one of only four auxiliary Interstate Highways to go into a state its parent route does not.

Route description

I-129 begins along US 20 on the western edge of South Sioux City, Nebraska, just west of exit 1, a

cloverleaf interchange A cloverleaf interchange is a two-level interchange in which all turns are handled by slip roads. To go left (in right-hand traffic; reverse directions in left-driving regions), vehicles first continue as one road passes over or under the ...

with US 75 and US 77. US 77 travels north through South Sioux City before ending at

Sioux City Sioux City () is a city in Woodbury and Plymouth counties in the northwestern part of the U.S. state of Iowa. The population was 85,797 in the 2020 census, making it the fourth-largest city in Iowa. The bulk of the city is in Woodbury County ...

while US 75 joins I-129 and US 20. later, I-129/US 20/US 75 intersect Dakota Avenue at a

partial cloverleaf interchange A partial cloverleaf interchange or parclo is a modification of a cloverleaf interchange. The design has been well received, and has since become one of the most popular freeway-to- arterial interchange designs in North America. It has also be ...

. U.S. Highway 20 Business (US 20 Bus.) 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 A Jersey barrier, Jersey wall, or Jersey bump is a modular concrete or plastic barrier employed to separate lanes of traffic. It is designed to minimize vehicle damage in cases of incidental contact while still preventing vehicle crossovers resu ...

instead of a grassy median. The three routes cross the Missouri River and immediately intersect

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

and I-129 ends.

History

After the passage of the

Federal-Aid Highway Act The following bills and Acts of Congress in the United States have been known as the Federal-Aid Highway Act or similar names: * Federal Aid Road Act of 1916: July 11, 1916, ch. 241, (first) * Federal Aid Highway Act of 1921 (Phipps Act): Novemb ...

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

. The proposed highway was planned to cost $22.5 million (equivalent to $ million in ), which included $15 million (equivalent to $ million in ) for the Missouri River bridge. On the 1973 state highway map, the

Iowa State Highway Commission The Iowa Department of Transportation (Iowa DOT) is the government organization in the U.S. state of Iowa responsible for the organization, construction, and maintenance of the primary highway system. Located in Ames, Iowa, DOT is also responsi ...

showed the planned route on the state map for the first time. I-129 was opened on November 22, 1976.

Exit list

References

{{s-end 29-1 29-1 29-1 U.S. Route 20 U.S. Route 75 1 Transportation in Dakota County, Nebraska Transportation in Woodbury County, Iowa