"It remains today one of the great bridge engineering accomplishments for railway and highway bridges built in the country."
- Historic American Engineering Record, Southeast Regional Office, National Park Service, U.S. Department of the Interior, 2005
By the late 1880s, New Orleans was being served individually by multiple railroad trunk lines. A committee of citizens decided that this wasn't the most efficient and economical way to provide rail service to the port area along the river. They decided that a belt railroad was needed to provide switching among the different trunks. Prior to the construction of the Huey P. Long Bridge, railcars and trucks had to be ferried across the river. With the construction of this bridge, the Port of New Orleans became better connected to the rail infrastructure on both banks.
Many conditions, such as the "gumbo soil" in and around the river, low land approaches, strong river currents, and the need for high navigation clearances required for ocean-going vessels, made the design and construction of this bridge difficult. Dr. Karl Terzaghi, who had developed a science of soil mechanics based on investigations of the permeability and compressibility of soil samples, concluded that the caissons of the four main piers should be sealed in a sand layer at a depth of approximately 170 feet snd that the fatigue loading should not be more than 5.5 tons per square foot. Prior to Dr. Terzaghi's involvement, it had been recommended that the main piers should be founded from 225 feet to 250 feet below Gulf level. Even when the widening of the bridge was started in 2006, it was determined that no changes to the caisson foundations were needed.
Designed by the firm of Modjeski, Masters and Chase, the Huey P Long Bridge was the first bridge to cross the Mississippi River at New Orleans. Its dual-track railroad portion was the longest, highest railroad bridge in the world at the time with a total length of 22,995 feet. The highway portion, 8,076 feet long, consisted originally of two lanes cantilevered off each side. This bridge opened up the southern portion of the country to improved transportation of commerce and people.