Interstate 15 in Utah

Interstate 15 (I-15) runs north–south in the U.S. state of Utah through the southwestern and central portions of the state, passing through most of the state's population centers, including St. George and those comprising the Wasatch Front: Provo–Orem, Salt Lake City, and Ogden–Clearfield. It is Utah's primary and only north–south interstate highway, as the vast majority of the state's population lives along its corridor; the Logan metropolitan area is the state's only Metropolitan Statistical Area through which I-15 does not pass. In 1998, the Utah State Legislature designated Utah's entire portion of the road as the Veterans Memorial Highway.

The Interstate passes through the fast-growing Dixie region, which includes St. George and Cedar City, and eventually most of the major cities and suburbs along the Wasatch Front, including Provo, Orem, Sandy, West Jordan, Salt Lake City, Layton, and Ogden. Around Cove Fort, I-70 begins its journey eastward across the country. The Interstate merges with I-80 for about 3 miles (4.8 km) from South Salt Lake to just west of Downtown Salt Lake City and merges with I-84 from Ogden to Tremonton. Along nearly its entire length through the state, I-15 winds its way along the western edge of a nearly continuous range of mountains (including the Wasatch Range in the northern half of the state). The only exceptions are when it passes through the mountains south of Cedar City and, again, north of Cove Fort.

From Las Vegas, Nevada, I-15 winds and slightly inclines through the Virgin River Gorge in northwest Arizona, then it crosses the border into Utah and Washington County. Just past the border, there is a port of entry on each side of the freeway. These ports of entry (weigh stations) are jointly operated by the states of Utah and Arizona and are the first northbound exit and last southbound exit on I-15 in Utah. Heading north-northeast, it continues with two lanes in each direction until it reaches an interchange with Southern Parkway (SR-7), which provides access to the St. George Regional Airport. After SR-7, the route turns north as it passes the Bloomington area of the City of St. George and an interchange at Brigham Road, where an auxiliary lane is added before it crosses the Virgin River. This marks the lowest elevation along I-15 in Utah, 2,560 feet (780 m) above sea level. Immediately north of the Virgin River and partially spanning the Santa Clara River, is the Dixie Drive interchange. A collector ramp is added between Dixie Drive and the next interchange with Bluff Street (SR-18). I-15 then narrows to two lanes in each direction and turns northeast again, where it passes the eastern side of downtown St. George, with an interchange at St. George Boulevard (SR-34). The Bluff Street and St. George Boulevard interchanges are the southern and northern ends of the St. George I-15 Business Loop. From this point north, I-15 generally follows the route of the Old US 91, maintaining a two-lane configuration until it reaches the Wasatch Front in the north-central part of the state. (The route of Old US 91, in turn, followed the older Arrowhead Trail highway to Salt Lake City.)

After leaving St. George, I-15 continues northeast and passes through the northern part of the city of Washington. An auxiliary lane is added between St. George Boulevard and Green Springs Road with additional interchanges at Washington Parkway and State Street (SR-9). Northeast of Washington, I-15 passes through the northwestern side of the town of Leeds, with one-way interchanges on the southwest and northeast ends of town. After passing through the northwestern part of Toquerville, and an interchange with SR-17 (at Anderson Junction), I-15 resumes a more north-northeastern course as it ascends about 1,000 feet (300 m) higher on the Colorado Plateau. Along the way, it passes through the areas of Browse and Pintura, with interchanges at both, as well as two more ranch exits further northeast. After its ascent, it passes by the east of side of Ash Creek Reservoir and then by the northwest corner of Zion National Park, with an interchange providing access to the Kolob Canyon area of the park. Next is an interchange that provides access to New Harmony (several miles west) and Kanarraville (several miles to the northeast). This interchange is also at the border of Washington County and Iron County.

Just after entering Iron County, I-15 reaches the southernmost rest areas along its route within the state (with one each, northbound and southbound). After passing about a mile (1.6 km) west of Kanarraville, it reaches an interchange in Hamilton Fort. The freeway then briefly turns nearly east before turning north again to pass through the west side of Cedar City. The first interchange is at the southern end of SR-130 (Main Street) and the Cedar City I-15 Business Loop. Just north is the 200 South (SR-56) interchange, which provides access to downtown Cedar City as well as the Cedar City Regional Airport. After this interchange, the freeway turns northeast before the final Cedar City interchange with SR-130 (once again). This interchange is also the northern end of the Cedar City I-15 Business Loop, although no longer indicated as such by signage. The freeway then passes by the eastern edge of Enoch, but without an interchange within that city. After an interchange within the area of Summit, I-15 heads east-northeast before passing by the northwest edge of Parowan, with interchanges on the west (200 South / SR-143) and north (Main Street / SR-274) sides of town. After Parowan, the freeway curves back to a northeast course as it passes about a mile (1.6 km) west of Paragonah and reaches an interchange on the north side of that city (SR-271). Continuing northeast, it reaches the next pair of rest areas before an interchange with SR-20 and then a ranch exit (exit 100) before leaving Iron County.

As I-15 enters Beaver County, the Interstate turns northwestward and winds its way through the mountain pass before heading north again to pass along the western edge of the city of Beaver. The southern and northern interchanges in Beaver include the I-15 Business Loop and SR-160—the city streets are South Main Street on the south and 1400 North on the north. Off the 1400 North interchange, there is an official rest stop, courtesy of Utah Department of Transportation (UDOT) and the local Texaco Station. The freeway then heads slightly westward until it passes by the western side of the community of Manderfield and curves back to a north-northeast course. After several miles, there is an interchange with Manderfield Road before I-15 winds through another mountain pass and reaches the Sulphurdale interchange. This mountain pass, with a summit located at milepost 124.8, is the highest point along I-15 in Utah, at 6,611 feet (2,015 m) above sea level. After passing west of the ghost town of Sulphurdale, it reaches the interchange with the western end of I-70. This interchange is on the border of Beaver and Millard counties.

North of the I-15/I-70 interchange, I-70 heads east to Richfield and then toward Denver, Colorado, while I-15 continues north to pass by Cove Fort on the east and reach the Cove Fort (SR-161/Black Rock Road) interchange. Off the Black Rock Road interchange is an official rest stop, courtesy of UDOT and the local Chevron Station. I-15 meanders to the north-northeast before straightening out to the northeast–southwest of Kanosh. The freeway passes by the northwestern side of Meadow, having an interchange with North Main Street (SR-133). It then passes through the western side of Fillmore. SR-99 follows the length of the I-15 Business Loop through Fillmore, connecting at 850 South on the southwestern part of town and North Main Street / Cedar Mountain Road on the northern city limits. Off the North Main Street interchange, there is an official rest stop courtesy of UDOT and the local Chevron Station. Continuing north-northwest, it has an interchange with 5400 North / Maple Hollow Road (SR-64) before passing by the southeast edge of Holden. Several miles northeast of Holden, US 50 merges with I-15 as it continues northeastward and eventually heading through a low mountain pass just after another ranch exit. The US 50 overlap then ends as I-15 passes through the northwestern corner of Scipio. Off the Scipio interchange, is an official rest stop courtesy of UDOT and Flying J. (US 50 eastbound serves as a connector to I-70 for southbound I-15 motorists.)

Several miles north of Scipio, I-15 leaves Millard County and enters Juab County before turning northeastward again. After an interchange with the Yuba Lake Road is another interchange at Mills Junction / SR-78 just southeast of Chicken Creek Reservoir. The freeway then continues roughly north-northeast until it turns northeast to pass through the southern part of Nephi and an interchange with South Main Street (SR-28). The freeway then turns north to pass through the eastern side of Nephi, with an interchange with 100 North (SR-132). It then curves to the north-northwest before reaching the interchange with the northern end of SR-28 about a mile (1.6 km) north of town. The Interstate then turns north and passes by the eastern side of Mona and has an interchange with SR-52 (300 North). Continuing north, it passes by the eastern edge of Rocky Ridge before promptly leaving Juab County and entering Utah County.