Interstate 129

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Interstate 129

I-129 highlighted in red
Route information
Auxiliary route of I-29
Length3.50 mi[1][2] (5.63 km)
Nebraska: 3.21 mi (5.17 km)
Iowa: 0.286 mi (460 m)
ExistedNovember 22, 1976[3]–present
NHSEntire route
Major junctions
West end US 20 in South Sioux City, Nebraska
Major intersections US 75 / US 77 in South Sioux City, Nebraska
East end I-29 / US 20 / US 75 in Sioux City, Iowa
CountryUnited States
Highway system
N-128NE N-133
Iowa 128IA Iowa 130

Interstate 129 (I-129) is an auxiliary Interstate Highway which connects South Sioux City to I-29 in Sioux City, Iowa. Opened in 1976, I-129 is a 3.5-mile-long (5.6 km) route, running 3.21 miles (5.17 km) in Nebraska. At 0.286 miles (0.460 km), 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 with US 75 and US 77. US 77 travels north through South Sioux City before ending at I-29 in Sioux City while US 75 joins I-129 and US 20. One mile (1.6 km) later, I-129/US 20/US 75 intersect Dakota Avenue at a partial cloverleaf interchange.[1] 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 instead of a grassy median. The three routes cross the Missouri River and immediately intersect I-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.[4] At I-29, US 20 and US 75 continue east around Sioux City and I-129 ends.


After the passage of the Federal-Aid Highway Act of 1968, the mileage which would eventually be manifested in over 1,400 miles (2,300 km) of Interstate Highway was allocated to the states. Iowa received the smallest allocation, 0.5 miles (0.80 km), for the southern bypass of Sioux City.[5] The proposed highway was planned to cost $22.5 million (equivalent to $163.89 million in 2023), which included $15 million (equivalent to $109.26 million in 2023) for the Missouri River bridge.[6] On the 1973 state highway map, the Iowa State Highway Commission showed the planned route on the state map for the first time.[7] I-129 was opened on November 22, 1976.[3]

Exit list

NebraskaDakotaCovington Precinct0.000.00
US 20 west
Western end of US 20 overlap; continuation beyond western terminus
US 75 south / US 77 – Fair Grounds, Sioux City
Western end of US 75 overlap; signed as exits 1A (south) & 1B (north)
South Sioux City1.502.412Dakota Avenue (US 20 Bus. east) – South Sioux City, Dakota City
Missouri River3.21
Sergeant Floyd Memorial Bridge; NebraskaIowa line
IowaWoodburySioux City0.2860.4601
I-29 / US 75 Bus. – Council Bluffs, Sioux Gateway Airport, Downtown Sioux City
Eastern end of US 20/US 75 overlap; signed as exits 1A (south) and 1B (north); I-29 exits 144A-B

US 20 east / US 75 north – Fort Dodge, Le Mars
Continuation beyond I-29
1.000 mi = 1.609 km; 1.000 km = 0.621 mi


  1. ^ a b c "Nebraska Highway Reference Log Book" (PDF). Nebraska Department of Roads. 2015. p. 270. Retrieved January 8, 2017.
  2. ^ a b "Road Network (Portal)" (ESRI shapefile). Ames: Iowa Department of Transportation. April 9, 2021. Retrieved April 18, 2021.
  3. ^ a b Iowa Department of Transportation. The National System of Interstate Defense Highways: 1956–1996.
  4. ^ Google (February 27, 2010). "Interstate 129" (Map). Google Maps. Google. Retrieved February 27, 2010.
  5. ^ Federal Highway Administration. "FHWA By Day - December 13". Retrieved August 1, 2010.
  6. ^ "Hot off the Wire". Carroll Daily Times Herald. Carroll, Iowa. June 2, 1972. p. 2. Retrieved August 9, 2014 – via
  7. ^ Iowa State Highway Commission (1973). State of Iowa Transportation Map (PDF) (Map). Ames: Iowa State Highway Commission. Sioux City inset. Retrieved August 1, 2010.
Browse numbered routes
Iowa 128IA Iowa 130
N-128NE N-133