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 route, running in Nebraska. At , 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.