Interstate 129

Interstate 129
Sioux City regional map with I-129 highlighted in red.
Route information
Auxiliary route of I‑29
Length:	3.48 mi (5.60 km) Nebraska: 3.21 mi (5.17 km) Iowa: 0.27 mi (0.43 km)
Existed:	November 22, 1976 – present
Major junctions
West end:	US 20 / US 75 / US 77 in South Sioux City, NE
	US 77 in South Sioux City, NE
East end:	I‑29 / US 20 / US 75 in Sioux City, IA
Location
States:	Nebraska Iowa
Highway system
Interstate Highway System Main Auxiliary Suffixed Business

Interstate 129 (I-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 3.48-mile-long (5.60 km) route, running 3.21 miles (5.17 km) in Nebraska. At 0.27 miles (0.43 km), Interstate 129 is the shortest highway in the state of Iowa. A rare characteristic of I-129 is that it is one of only four Interstates to enter a state that its parent does not enter (I-29, in this case, does not enter Nebraska). The other three are I-275 around Cincinnati, Ohio since I-75 does not enter Indiana, I-287 around New York City because I-87 does not enter New Jersey, and I-535 because I-35 (located in the Duluth-Superior area) does not enter Wisconsin.

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 (1.6 km) 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 1,400 miles (2,300 km) of interstate highway was allocated to the states. Iowa received the smallest allocation, one-half mile (800 m), for the southern bypass of Sioux City. The proposed highway was planned to cost $22.5 million ($127 million in 2024), which included $15 million ($84.9 million in 2024) 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.

Exit list

State	County	Location	mi	km	Exit	Destinations	Notes
Nebraska	Dakota	South Sioux City	0.00	0.00		US 20 west	West end of US 20 overlap
			0.38	0.61	1A	US 75 south / US 77 south – Fairgrounds	West end of US 75 overlap
			0.40	0.64	1B	US 77 north – Sioux City
			1.50	2.41	2	South Sioux City, Dakota City
Missouri River			3.21 0.000	5.17 0.000	Nebraska–Iowa state line
Iowa	Woodbury	Sioux City	0.286	0.460	1	I‑29 / US 75 Business north – Council Bluffs, Downtown Sioux City	Signed as exits 1A (southbound) and 1B (northbound); I-29 exits 144A-B
						US 20 east / US 75 north – Fort Dodge, Le Mars	East end of US 20 / US 75 overlap
1.000 mi = 1.609 km; 1.000 km = 0.621 mi       Concurrency terminus

References

Browse numbered routes
← x20px Iowa 128	IA	Iowa 130 →
← N-128	NE	N-133 x20px →