History

Before I-15 was built, US 91 was the thoroughfare that ran north-south through Utah. Only in the far north of the state is I-15 built closer to the US 191 corridor.

The corridor of US 91 was largely paved in the 1920s. In 1927 there was still a long stretch from the Arizona border to Nephi that was unpaved, but this stretch was paved at a very rapid pace in the years that followed, by 1932 the entire route was asphalted. In the mid-1930s, the last section of US 191 in the far north of Utah was paved. Utah completed the asphalting of the north-south route earlier than Idaho.

As early as the 1940s, significant portions of the Provo – Salt Lake City – Ogden – Brigham City corridor had been widened to 4 lanes, which at the time was called a “superhighway” but was not yet a highway. Finally, in the early 1950s, passage through American Fork was widened to four lanes, as well as a missing section between Ogden and Brigham City. Before the construction of the Interstate Highways began, a 165-kilometre stretch had already been widened to at least 4 lanes. Part of this corridor still exists today but is now as US 89numbered, except between Salt Lake City and Ogden, where current US 89 has no relation to the original four-lane US 91. US 91 was canceled in 1974 due to the construction of I-15 over the existing route, due to a double numbering of many hundreds of miles.

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Construction history

Construction of I-15 in Southern Utah

Construction on I-15 began shortly after the creation of the Interstate Highway system in southern Utah in 1956, with the first section of I-15 opening about 1960 between Toquerville and Kanarraville. This was the very first section of I-15 to appear on Utah’s official state highway map under that number. This section runs along the Black Ridge and is one of the more spectacular sections of I-15 in Utah.

A second section opened a year later between Manderfield and Sulfurdale, over a 2,062 m high mountain pass. In the early 1960s, these sections were further extended. A major opening followed in 1965 at the historic Cove Fort, when the interchange with I-70 opened. In 1967, I-15 to the south side of Cedar City was completed. This made it possible to continue driving a 75 kilometer long route from near St. George to Cedar City.

In 1967, southern Utah had three missing sections, from the Arizona border to Washington at St. George, a longer stretch from Cedar City to Beaver, and a longer stretch from Kanosh to Santaquin, which is at the southern end of urbanized Wasatch. Front is located.

The southernmost portion of I-15 was built in conjunction with the State of Arizona because it crosses the Virgin River Gorge in Arizona, which previously had no roads at all, so there could be no temporary terminus. Opened on December 14, 1973, the section in Arizona is considered one of the most spectacular highways in the United States. At that time, there was a 132-mile stretch from the Arizona border to Paragonah throughput. About 1980, the last missing section opened in southern Utah between Paragonah and Beaver. This allowed for a 200-mile stretch from the Arizona border to Scipio, leaving only one missing link between Scipio and Nephi. This last 65-kilometre stretch was completed in the early.

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van	nasty	length	datum
Exit 27 Toquerville	Exit 42 Kanarraville	24 km	00-00-1960
Exit 120 Manderfield	Exit 129 Sulphurdale	14 km	00-00-1961
Exit 22 Leeds	Exit 27 Toquerville	7 km	00-00-1962
Exit 112 Beaver (north)	Exit 120 Manderfield	13 km	00-00-1964
Exit 10 Washington	Exit 22 Leeds	19 km	00-00-1965
Exit 42 Kanarraville	Exit 51 Hamilton Fort	14 km	00-00-1965
Exit 129 Sulphurdale	Exit 135 Cove Fort	10 km	00-00-1965
Exit 135 Cove Fort	Exit 146 Kanosh	17 km	00-00-1966
Exit 42 Kanarraville	Exit 57 Cedar City (south)	21 km	00-00-1967
Exit 57 Cedar City (south)	Exit 62 Cedar City (north)	8 km	00-00-1968
Exit 62 Cedar City (north)	Exit 71 Summit	14 km	00-00-1969
Exit 109 Beaver (south)	Exit 112 Beaver (north)	5 km	00-00-1970
Exit 0 Arizona state line	Exit 10 Washington	16 km	14-12-1973
Exit 71 Summit	Exit 82 Paragonah	18 km	00-00-1973
Exit 158 Meadow	Exit 167 Fillmore (north)	14 km	00-00-1973
Exit 146 Kanosh	Exit 158 Meadow	19 km	00-00-1974
Exit 167 Fillmore (north)	Exit 178 Holden (north)	18 km	00-00-1976
Exit 228 Nephi (north)	Exit 244 Santaquin	26 km	00-00-1976
Exit 95 State Highway 20	Exit 109 Beaver (south)	23 km	00-00-1978
Exit 178 Holden (north)	Exit 188 Scipio	16 km	00-00-1979
Exit 82 Paragonah	Exit 95 State Highway 20	21 km	00-00-1980
Exit 188 Scipio	Exit 228 Nephi (north)	64 km	00-00-1984?

Construction of I-15 in the Salt Lake City Area

Construction on I-15 began in 1950. The first section opened in 1956 north of Salt Lake City, a short stretch that coincided with US 89 and was not mapped until I-15 was signposted when the Bountiful diversion was also made in 1960. was opened. Construction of I-15 gained momentum in the early 1960s, with the upgrade of US 89 between Lehi and Draper over the low mountain pass and the construction of I-15 over a new route in south Salt Lake City. These parts were opened in 1964-1965. Beginning in 1965, a 17-mile stretch through Salt Lake City was continuous.

Construction then progressed south of Salt Lake City, where the land was only slightly suburbanized at the time. The Draper-Murray section was completed in stages between 1967 and 1971, completing I-15 through Salt Lake County.

Further south in Utah County, it was initially built at the conversion of US 91 between Lehi and Draper, across “The Point,” a low mountain pass that separates Utah County from Salt Lake County. However, this project took a relatively long time and was not fully completed until 1971. The section of I-15 between Provo and Lehi opened earlier, around 1964, this section was constructed more westerly than the old US 91 over a new route. By 1967, the remaining portion of I-15 in southern Utah County was completed, opening a 21-mile stretch from Santaquin to Provo.

North of Salt Lake City, the extension from Bountiful to Ogden was built in the first half of the 1960s. This was only partially constructed over the existing four-lane US 91, but largely over a new route that was opened in two or more phases around 1963 and 1965. This made it possible to drive 66 kilometers of I-15 from the south of Salt Lake City to Ogden.

Two sections of I-15 were not considered Interstate Highways for some time, a section across “The Point” from Lehi to Draper and a somewhat longer stretch from Centerville to Layton north of Salt Lake City. These were the older sections of US 91 that were converted into a highway, but only received I-15 status in 1974.

Van	Unpleasant	Length	Datum
Exit 310	Exit 313	5 km	00-10-1956
Exit 313	Exit 317	6 km	02-11-1960
Exit 317	Exit 330	21 km	00-00-1963
Exit 306	Exit 310	6 km	30-10-1964
Exit 265	Exit 282	27 km	00-00-1964
Exit 303	Exit 306	5 km	19-04-1965
Exit 300	Exit 303	5 km	23-11-1965
Exit 330	Exit 341	17 km	00-00-1965
Exit 244	Exit 265	34 km	00-00-1967
Exit 291	Exit 300	14 km	1967-1971
Exit 282	Exit 291	14 km	1970-1971

Construction of I-15 in northern Utah

In about 1963, the first section of northern Utah was completed, a new section of I-15 between Brigham City and Tremonton, beginning and ending at US 191. In 1965, the Brigham City bypass opened to traffic. In 1970, the first section opened from Ogden to the north and was completed in 1972 to Brigham City. This made it possible to drive through I-15 from Santaquin to Tremonton over a length of 210 kilometers.

About 1977, the northernmost portion of I-15 opened, between Plymouth and the Idaho border. There was still a missing link for a relatively long time, I-15 at Tremonton became I-84 towards Boise, but the exit to the north was missing for a long time. This 13-mile stretch between the interchange with I-84 at Tremonton and Plymouth opened on November 20, 1990. This was also the last section of the entire I-15 in the United States to open.

Van	Unpleasant	Length	Datum
Exit 365 Brigham City	Exit 376 Tremonton (south)	18 km	00-00-1963
Exit 357 Willard	Exit 365 Brigham City	13 km	00-00-1965
Exit 341 Ogden	Exit 351 South Willard	16 km	00-00-1970
Exit 351 South Willard	Exit 357 Willard	10 km	00-00-1972
Exit 376 Tremonton (south)	Exit 379 I-84	5 km	00-00-1973
Exit 392 Plymouth	Exit 401 Idaho state line	14 km	00-00-1977
Exit 379 I-84	Exit 392 Plymouth	21 km	20-11-1990

Later adjustments

Payson – Spanish Fork

In 2013-2015, a 15-kilometer stretch between Exit 248 in Payson and Exit 257 in Spanish Fork was widened from 2×2 to 2×3 lanes. This followed on from the widening completed in 2012 further from Spanish Fork to Lehi.

I-15 CORE

I-15 in South Salt Lake City.

On November 5, 2012, the I-15 Utah County I-15 Corridor Expansion (39-mile) project was completed, which will see I-15 widened by 2 lanes in each direction. Between Exit 257 and Exit 258, the highway has been widened from 2×2 to 2×3 lanes, then from 2×3 to 2×5 lanes to Exit 269 in Orem and from 2×4 to 2×6 lanes to Exit 279 in Lehi. Utah also has the longest express lane in the United States over a length of 100 kilometers, in both directions. The project cost $1465 million. The entire I-15 has actually been rebuilt.

The Point Project

Called ‘The Point Project’, a 10-mile stretch from Lehi (Exit 279) and Draper (Exit 289) south of Salt Lake City has been widened from 2×4-2×5 to 2×6 lanes, including an express lane and a DDI with the State Route 92. The work cost $252 million and was completed between March 2015 and October 2016.

Between 2018 and 2020, a missing portion in Lehi was further widened to 2×6 lanes between Main Street in Lehi and the connection to The Point Project in northern Utah County. This project was completed on October 30, 2020.

Salt Lake City

In anticipation of the 2002 Olympic Games held in Salt Lake City, I-15 along downtown has been completely reconstructed. Both interchanges with I-80 have been completely redeveloped and a brand new interchange with State Route 201 has been constructed. A 4×4 lane parallel structure has also been constructed between the southern interchange with I-80 and Downtown Salt Lake City. During the work in the 1990s, only 2×2 lanes were temporarily available, a huge difference from the situation after the completion of the project.

Salt Lake City – Farmington

Between April 2014 and August 2015, express lanes were added to I-15 between North Salt Lake and Farmington. This project cost $117 million.

Farmington – Ogden

When the Legacy Parkway opened in 2008, a major interchange with I-15 was created in Farmington. I-15 to Kaysville was also widened to 2×4 lanes at the time. In 2010, I-15 was widened to 2×4 lanes further up to Hill Field Road in Layton, and a new SPUI with Layton Parkway was also constructed.

Ogden – Brigham City

I-15 originally had 2×2 lanes north of I-84 in Ogden. The merger created significant congestion, and in 2007-2008 the highway was widened to 2×4 lanes from I-84 to 1200 S in Ogden and 2×3 lanes further to 2700 N in Farr West. In 2016, I-15 was widened to 2×3 lanes further north to 1100 S in Brigham City.

Future

I-15 now has a minimum of 2×3 lanes from Exit 248 in Payson to Exit 362 in Brigham City, a distance of 183 kilometers.

Traffic intensities

I-15 near Nephi, with a view of Mount Nebo (3635 m).

20,000 vehicles drive daily on the Arizona border, rising to 30,000 vehicles in St. George. Halfway between St. George and Cedar City, 21,000 vehicles and 16,500 vehicles drove north of Cedar City. There were 16,400 vehicles south of I-70 at Cove Fort and 12,400 vehicles north of it. At Scipio, 14,000 vehicles drove up to 21,000 vehicles north of Nephi. 43,000 vehicles drove between Payson and Spanish Fork.

After that, the I-15 runs through urban areas for a long time and the intensities are higher. North of US 6 in Spanish Fork, 77,000 vehicles ran, rising to 98,000 vehicles south of Provo and 105,000 vehicles between Provo and Orem. Between Orem and American Fork, 131,000 vehicles and 120,000 vehicles drove at Lehi. In Draper, 164,000 vehicles drove up to 232,000 vehicles south of I-215 in West Jordan. There were 213,000 vehicles south of I-80 and 252,000 vehicles north of it. There were 128,000 vehicles north of I-80 at Downtown Salt Lake City, rising again to 143,000 vehicles north of I-215 at North Salt Lake.

128,000 vehicles passed through Centerville and 109,000 vehicles passed through Kaysville. 110,000 vehicles passed Clearfield and 96,000 vehicles passed Ogden, just north of I-84. This then steadily declines to 27,000 vehicles at Brigham City and 18,000 vehicles at Tremonton. 9,000 vehicles were still driving at the Idaho border.

Lane Configuration

Van	Unpleasant	Lanes	Comments
Exit 0	Exit 248	2×2	southern Utah
Exit 248	Exit 258	2×3	Payson – Spanish Fork
Exit 258	Exit 269	2×5	Provo
Exit 269	Exit 291	2×6	American Fork – Draper
Exit 291	Exit 295	2×5	Salt Lake City
Exit 295	Exit 298	2×6	Salt Lake City
Exit 298	Exit 304	2×5	Salt Lake City
Exit 304	Exit 305	4×4	Salt Lake City
Exit 305	Exit 308	2×6	Salt Lake City
Exit 308	Exit 313	2×3
Exit 313	Exit 324	2×4
Exit 324	Exit 362	2×3	Ogden – Brigham City
Exit 362	Exit 398	2×2