Interstate 129 crosses the Missouri River between Sioux City, Iowa, and southern reaches of South Sioux City, Nebraska. The freeway is cosigned with U.S. 20 and U.S. 75 for its short distance.
I-129 spans the Missouri River across the Sergeant Floyd Memorial Bridge, a 2,607 foot long steel plate girder bridge. The bridge accommodates four lanes of travel with a 79 foot deck at a height of 64 feet above the river.
Mileage for the Sergeant Floyd Memorial Bridge was added to the Interstate Highway System in late 1968. The route was announced in Sioux City on December 13, 1968 and approved by the American Association of State Highway Officials (AASHO) on June 23, 1969. The 1.7 mile long approach on the Nebraska side of the river, the bridge and the interchange with I-29 cost $36,660,490. The span was dedicated on the morning of November 22, 1976.1 The Nebraska portion opened a year later.2
The east end of I-129 ties into the Sioux City bypass along U.S. 75. Conceptualized in the early 1970s, the bypass wraps around eastern reaches of the city to a point just south of the Plymouth County line. Earth work started on the route north of U.S. 20 in 1997.3
Totaling $45 million, with federal funding paying for 80% of the costs, the U.S. 75 bypass from U.S. 20 northward opened following a ribbon cutting ceremony held on November 19, 2001. The old route through the city was redesignated as U.S. 75 Business. Coupled with the project also was the $1.7 million construction of Outer Drive / 28th Street, a 1.3 mile long roadway linking north Sioux City with U.S. 75 at Exit 97.3
Signs for Interstate 129 posted on I-29 in Iowa referenced “I-129” in text in place of tri-color shields during the 2000s. An inquisition regarding the signing practice to IowaDOT netted this response in May 2007:
We received your comment concerning the use of the interstate shield for I-129 for southbound traffic and the use of letter text for I-129 for northbound traffic on I-29. Approximately 10+ years ago some motorists were getting confused with I-129 signing, thinking it was I-29 and taking the off ramp to US75 to Nebraska when they really wanted to stay on I-29. We thought we would try using the letter text I-129 to make it stand out different from the interstate shield of I-29.
Since then we have had a signing project on southbound I-29 and changed the letter text I-129 back to the interstate shield and have had no complaints or concerns that I’m aware of. The northbound signing on I-29 will be reviewed when we put our next project together.
All text-based signs for I-129 were replaced by June 2015 with the exception of a remaining panel over the southbound ramp split of Exit 144.
Interstate 429 Beltway
A post on the Usenet group misc.transport.road indicated that 7.2 mile bypass for U.S. 75 opened in 2001 was to become a part of Interstate 129 and that longer range plans for 2004-08 would extend the freeway west over ten miles to I-29 north of North Sioux City. Initial construction proposed for 2004 on the South Dakota side would construct the route as Interstate 429. Upon completion of the two sections, the beltway would be renumbered as just I-129.4
The Interstate 429 beltway was outlined by Don Willoughby, manager of government and community affairs for IBP, inc. Touting economic development and reduced congestion, Willoughby indicated that the proposal could take up to 20 years. The Tri-State Governors’s Conference held in South Sioux City, Nebraska on July 25, 2000 discussed various roads and infrastructure improvements including I-429. Sioux City Councilman Todd Moss asked the South Dakota Department of Transportation to conduct an interstate corridor study along Interstate 29 between Exit 4 (Northshore Drive) and milepost 6, including a new interchange (Exit 5) for the future beltway. Countering the proposal was South Dakota Governor Bill Janklow, who indicated that a lack of resources would prohibit any prospects for constructing the roadway.5
Interstate 129 was never extended north and the I-429 proposal never came to pass. The freeway along U.S. 75 defaults onto the divided highway leading northeast to Hinton and Le Mars. The US route in conjunction with Iowa 60, MN 60 and U.S. 59 provides an expressway grade corridor to Worthington, Minnesota and Interstate 90.