U.S. 91

The remaining 45.27 miles of U.S. 91 in Utah originate at a diverging diamond interchange with I-15/84 at Brigham City. U.S. 91 overlaps with U.S. 89 from Brigham City northeast to Logan. U.S. 91 continues from there north to North Logan, Hyde Park, Smithfield, Richmond and into Idaho beyond Lewiston.

U.S. 91 combines with U.S. 89, 2.008 miles east of I-15/84 across the south side of Brigham City. U.S. 89/91 overlap east through Box Elder Canyon and north along the Wellsville Mountains to Wellsville Canyon. The two routes emerge in Cache Valley at Wellsville.

Originally beginning in Long Beach, California, U.S. 91 was truncated northward to Baker, California in 1965. The remainder of the route in California, all of it in Nevada, and within the Beehive State north to Brigham City was eliminated in 1974.

Within Utah U.S. 91 was replaced by Interstate 15 and a series of state routes, mostly in urban areas. Through southwest Utah, U.S. 91 entered the state from Arizona via Mohave County Route 91, following what is now Old Highway 91 to Castle Cliff and the Beaver Dam Mountains. The highway climbed onto Utah Hill Summit as it traversed the Beaver Dam Mountains. Old Highway 91 makes a gradual eastern arc, passing through Shivwits and paralleling the Santa Clara River southeast into the cities of Ivins and Santa Clara. Santa Clara Drive extends the former route east to Sunset Boulevard in St. George. The eastern 1.303 miles of Sunset Boulevard are state maintained and designated as Utah State Route 8.

U.S. 91 turned south onto Bluff Street (SR 18) to St. George Boulevard (SR 34) east through Downtown St. George. The US highway converged with I-15 just ahead of Red Cliffs Drive. Old U.S. 91 was directly replaced with I-15 northeast across Middleton Black Ridge to where Red Cliffs Drive diverges from the freeway east to Telegraph Street into Washington. All of Telegraph Street northeast to Utah 9 is old U.S. 91. Old Highway 91 resumes in name from there and continues north to eventually run along the east side of Interstate 15 to Leeds.

East

1100 South heads east from 1600 West into the diverging diamond interchange (Exit 362) joining U.S. 91 with I-15/84.
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I-15/84 overlap south from Brigham City to Ogden and north to Tremonton.
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Originally a trumpet interchange joined the end of U.S. 91 with I-15/84. It was later changed to a diamond interchange, and then a DDI in 2014.
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Exit 362 from I-15/84 south
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I-15 travels north from Tremonton to Pocatello and Idaho Falls in southeastern Idaho. I-84 heads northwest to Twin Falls and Boise in the Gem State.
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U.S. 91 runs across the south side of Brigham City between I-15/84 and U.S. 89 at SR 13. U.S. 89/91 overlap northeast to Logan.
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U.S. 91 is initially signed with an east cardinal direction banner instead of north.
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U.S. 91 constitutes a controlled access arterial, with two at-grade intersections between I-84/91 and U.S. 89 and SR 13 (S Main Street).
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U.S. 89 converges with U.S. 91 north from the city of Perry. SR 13 south ties in from Main Street and Downtown Brigham City.
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Business Loop I-15/84 through Brigham City followed U.S. 91 east and SR 13 north. Shields for the route were removed from U.S. 91 east by August 2018.
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U.S. 89 combines with U.S. 91 east from Brigham City through Box Elder Canyon four miles to the town of Mantua.
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West

U.S. 91 extends west along 1100 South from U.S. 89 and SR 13 (Main Street) for 2.01 miles to I-15/84.
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775 West (Medical Drive north / Commerce Way south) intersects U.S. 91, 062 miles west of U.S. 89/SR 13 (Main Street).
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U.S. 91 west spans a Union Pacific Railroad line ahead of I-15/84.
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I-15/84 overlap for 38.41 miles from Ogden and Riverdale north to Tremonton in Bear River Valley.
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Costing $14 million to build, the DDI at the south end of U.S. 91 was the first in northern Utah. It opened to traffic on September 16, 2014.¹
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Beyond their separation, I-84 travels east across the Wasatch Range to I-80 at Echo. I-15 continues south into Salt Lake City.
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West from U.S. 91, 1100 South ties into 1600 West, the west side frontage road for I-15/84.
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