At both historic ends of the highway in Iowa, bridge failures have caused US 77 to be detoured around Sioux City.

[4] In 1951, Gordon Drive, which carried US 20 east of the Combination Bridge, was extended westward along the banks of the Missouri River.

[5][6] In the late 1950s when construction of I-29 began, its route was planned along the banks of the Missouri River generally following the path of US 275, US 75, and US 77.

The first section of I-29, from a point along Gordon Drive east of the Combination Bridge to the Big Sioux River opened around October 1, 1958.

[8] After sections of I-29 in South Dakota opened up, allowing traffic to utilize bridges crossing the Big Sioux that were built in 1958, US 77 was moved onto the interstate completely.

An investigation of the collapse found the surging waters scoured the dirt and rocks away from around the bridge piers, which caused them to fail.

During routine bridge washing on May 6, 1982, an Iowa DOT worker discovered a 30-inch-long (76 cm) crack across a box girder.

The completion of Interstate 29 in South Dakota, which generally followed US 77 northward, meant the end of the U.S. Highway's importance.

Maps published by the Iowa DOT in 1983 and traffic logs from 1984 show and list US 77 extending into South Dakota.

[12][13] Highway maps and traffic logs from 1986 show US 77 ending at I-29, meaning the route was shortened at some time in those two years.