Interstate 15

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Interstate 15 cuts through the northwest corner of Arizona in Mohave County, separated from the rest of the state by the Grand Canyon. It passes through the Virgin River Canyon, one of the engineering marvels of the Interstate Highway System.

Interstate 15 Arizona Guides

Interstate 15 was part of the 1958 Interstate Highway system plan. The first leg constructed was the simplest one in Arizona, replacing U.S. 91 between Mesquite, Nevada and Littlefield.

However between Littlefield and Utah, Interstate 15 was proposed along a new alignment through the Virgin River Gorge. Despite objections from the state of Arizona, who advocated placing the road two miles north of the gorge for cost reasons, the Federal Highway Administration (FHWA) insisted on routing I-15 along the Virgin River, due to the scenic beauty of the gorge.

The section from Mesquite to Littlefield was constructed between 1961 and 1962, and opened to traffic in January 1963. Due to engineering difficulty, the section through the Virgin River Gorge was delayed. The first contracts were awarded in 1966, after completion of the road northeast of the gorge.

Due to the Vietnam War, the Federal government cut highway funds back 17% in December 1966. Arizona halted all work on I-15 through the gorge as a result, because the project had no benefit to the state. Utah had already completed the connecting section of I-15 between St. George and the Arizona state line, and found itself in a dilemma. Due to the importance of I-15 to Utah, and to avoid reconstructing U.S. 91, Utah advanced portions of their federal highway funds to Arizona in April 1969 to allow completion of I-15.

The majority of the freeway was completed by February 1972. The Virgin River was rechannelled twelve times during construction. During early building tests, a 50 foot long pile was driven into what was thought to be bedrock, only to have sank without a trace by the next morning. The Upper and Middle Gorge sections, located approximately between mile markers 15-26, were the first two to be built. The last section constructed was the Lower Gorge, approximately mile markers 11-15. The 3.82 mile long section of the Lower Gorge, where the gorge narrowed to as little as 150 feet in width, cost $13.8 million dollars to build. This segment of I-15 was the most expensive section of Interstate highway constructed, a distinction held until the completion of the Big Dig in Boston.

The last section of Interstate 15 in Arizona opened on December 14, 1973. Rendering U.S. 91 obsolete, this milestone lead to the decommissioning of U.S. 91 in 1974. Downgraded to County Route 91, old U.S. 91 remains driveable from Littlefield to St. George. I-15 spans the Virgin River six times inside the gorge, with the first bridge along the northbound roadway crossing the river lengthwise.

    Page Updated 02-12-2022.

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