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 Future

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.

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.