Meridian Highway Bridge is a bridge that formerly carried U.S. Route 81 across the Missouri River between Nebraska and South Dakota. It was the last link of the Meridian Highway, which became U.S. Route 81, to be completed.
It was designed for use by trains on the lower level of the bridge and vehicular traffic on the upper level; a lift mechanism allowed river traffic to pass below. However, trains never used the lower level.
In 1953, all tolls were lifted and the two levels were converted to one-way traffic, northbound on the top, southbound on the bottom. It is notable as the first permanent river crossing in the Yankton vicinity and as one of the final links in the Meridian Highway, an early north-south route from Winnipeg, Canada, to Mexico City, Mexico.
The vertical lift design was a typical period engineering solution to a typical problem of spanning a wide navigable river, and thus did not garner much attention in engineering circles in the 1920s.
The bridge was built with a double deck in anticipation that the lower deck would be made available to a railroad, but the line never materialized. The double decking speaks to the optimism of the bridge company founders that they could attract a north-south rail line to Yankton.
By the 1920s, however, the great era of railroad construction was over; many railroads were already contemplating abandoning unprofitable lines and consolidating parallel, competing lines. The bridge has undergone several rehabilitation projects including the construction of new approach spans, deck modifications and several structural steel repairs within its 76-year life.
The most significant alteration to the bridge occurred in 1983 when the lift span ceased to be movable and the operating machinery, operator’s house that was cantilevered off the northeast quadrant, and counterweights and cables were removed.
The towers remain, defining what the vertical lift span was. The decorative iron railings were replaced with concrete barricades. The bridge retains its original configuration and is today distinguished as the only vertical lift span in Nebraska and South Dakota.
The Waddell and Harrington design operated on the same principal as a counterbalanced window sash. It employed, according to the company, “a simple span equipped with machinery for operation, suspended at each end by wire ropes which pass over sheaves on towers and connect to counterweights about equal to the span weight.”
In its plans for the Yankton Bridge, the engineers incorporated a standard, Waddell and Harrington vertical-lift span, measuring 250 feet in length with a maximum lift of 27 feet. Like the bridge’s six fixed spans, the movable span was a heavy, rigid-connected Pratt truss with flat upper chords, predominantly channel-section web, and concrete piers.
In 1969 the bridge’s south approach was partially rebuilt. All of the remaining approach spans were replaced in the early 1980s, creating the present configuration of seven steel-girder shore spans on the north, twelve on the south.
At that time the lift span was deactivated and the counterweights removed from the towers. These later alterations were supervised by the Nebraska Department of Roads, although the bridge remains in South Dakota ownership.