Interstate 8

San Diego (Ocean Beach), CA ↔ Casa Grande, AZ•348.25 miles•0 Branch Routes

Overview

I-8 east - Sea Level — Well removed from the Pacific Ocean, Interstate 8 lowers to Sea Level in the Imperial Valley of California. 01/27/06

The lowest freeway in the country at one point, as it drops below sea level in the Imperial Valley near El Centro, Interstate 8 also traverses several mountain passes en route between San Diego, California, and Casa Grande, Arizona. Beginning in the Ocean Beach neighborhood, I-8 proceeds east along an urban course through the San Diego metro area. Beyond El Cajon and Alpine, the freeway winds through Cleveland National Forest and Laguna Mountain range before angling southeast. I-8 passes through the In-ko-pah Gorge ahead of Ocotillo and the rolling desert hills and farmland in the Imperial Valley. The freeway enters Arizona at the Colorado River and Yuma, and advances east across more desert terrain, including the famed Arizona saguaro. I-8 concludes at I-10 midway between Phoenix and Tuscon.

Mileage by State

California	169.92 mi
Arizona	178.33 mi

Data Sources

December 31, 2021 Interstate Route Log and Finders List

Parallel U.S. Routes

Interstate 8 only intersects one U.S. route for its entire length, U.S. 95, thus lending credibility to the paucity of U.S. highways in the Southwestern United States. However, it parallels a well-preserved historic U.S. route, Old U.S. 80.

U.S. 80 follows Interstate 8 from San Diego to Gila Bend, Arizona, where U.S. 80 turned north along what is now Arizona Route 85 to Interstate 10 near Buckeye. Well-preserved stretches of Highway 80 are otherwise accessible as frontage roads and county roads along the freeway corridor.

The easternmost stretch of I-8 between Gila Bend and Casa Grande was not a former U.S. route; the Interstate instead replaced former SR 84. (A shorter section remains close to Casa Grande.)

History

Origins of Interstate 8 in San Diego date back to 1957 with construction for a new U.S. 80 freeway between U.S. 395 and Ward Road. The majority of the U.S. 80 freeway was completed east from U.S. 101 to El Cajon by the early 1960s, with I-8 formally posted in 1964. Originally, I-8 was planned to end at Interstate 5. However, with the construction of the Ocean Beach Freeway (former California State Route 109), the route was extended west to the intersection of Nimitz Drive and Sunset Cliffs Boulevard.

The Pine Valley Creek Bridge opened to traffic in 1975. This segmental balanced cantilever bridge carries the freeway over 200 feet above the valley floor.¹ A more detailed history for I-8 posted at the Interstate 8 California guide.

Interstate Highway System Low Point — The lowest point on the entire Interstate Highway System (excluding underwater tunnels) is located on Interstate 8 at this point, when the freeway crosses the New River at an elevation of 52 feet below sea level. The lowest point is located near Exit 107 (Drew Road), which is west of El Centro in California's Imperial Valley. Further west, I-8 climbs to over 4,000 feet above sea level to cross the Cuyamaca Mountains. 01/27/06

Within Arizona, the earliest sections of Interstate 8 completed ran between Sentinel (Exit 87) and Piedra (Exit 102) and from Gila Bend (Exit 119) to SR 84 (Exit 151) in 1959. The Colorado River bridge west of Yuma opened in 1979 as the last portion of I-8 opened overall. See the Interstate 8 Arizona guide for a more detailed time line.

San Diego, CA - 1967 — Interstate 8 ended at I-5 until 1971, when the Ocean Beach Freeway was renumbered from SR 109 to I-8. U.S. 80 was decommissioned formally by the state of California in 1964, but signs remained along I-8 until 1972.

Southwestern Arizona - 1963 — Long pieces of Interstate 8 were open by 1963 along U.S. 80 through San Cristobal Valley and across Sentinel Plain and over SR 84 between the Sand tank and Maricopa Mountains and across Vekol Valley. Within Arizona, U.S. 80 was truncated from Yuma east to Benson in 1977. The remainder was dropped in 1989.

I-8/15 Cloverstack Interchange - Mission Valley — I-8 and I-15 meet at a multi-level interchange adjacent to the site of SDCCU Stadium (former home of the San Diego Chargers) in Mission Valley, San Diego. 09/02/06

East End ‐ Casa Grande, AZ

East at

Interstate 8 ends at a trumpet interchange (Exit 178) within southeastern reaches of the Casa Grande city limits. 04/26/17

West at

Interstate 10 continues northwest from I-8 to Phoenix, Chuckwalla Valley, Coachella Valley, and ultimately the Los Angeles Basin. 07/08/19

I-10 west three miles from I-8 - Casa Grande, AZ

East at

I-10 advances a half mile southeast from Jimmie Kerr Boulevard (old SR 84) to Interstate 8 in south Casa Grande. 04/26/17

West

The first confirming marker for Interstate 8 west. I-8 travels 60 miles west from I-10 to Gila Bend and 176 miles to Yuma. 04/26/17

East End – Past Views ‐ Casa Grande, AZ

Past Views Gallery (Tap to Expand / Collapse Section)

at

Button copy overheads at the separation of Exit 178A/B. The Picacho Mountains rise along the eastern horizon. Photo by Alan Hamilton (08/02).

West End - Sunset Cliffs Blvd / Nimitz Blvd ‐ San Diego (Ocean Beach), CA

West

Two lanes depart from I-8 west for Mission Bay Drive north and Sports Arena Drive south. Spanning the San Diego River, Mission Bay Drive heads to Mission Beach and Pacific Beach. Sports Arena Drive continues the arterial southeast through the Midway-Sports Arena District, which houses Pechanga Arena San Diego (San Diego Sports Arena). 07/19/21

I-8 west at Sunset Cliffs Blvd - San Diego, CA

Sunset Cliffs Blvd - North at

Sunset Cliffs Boulevard crosses the San Diego River to enter the Mission Bay Interchange with Sea World Drive, Ingraham Street and W Mission Bay Drive. During hot summer afternoons, Sea World Drive can be extremely congested with beach traffic trying to make its way back to Interstate 5. 04/25/20

Nimitz Blvd – North at

Two lanes continue north from Nimitz Boulevard toward Sea World Drive and Mission Bay Park. Sea World Drive winds east to I-5 at the exchange north of Interstate 8. 07/13/18

East

Interstate 5 (San Diego Freeway) heads south from I-8 to Downtown San Diego and Chula Vista. Interstate 8 advances east to Mission Valley, San Diego State University (SDSU) and the cities of La Mesa and El Cajon. 07/19/21

I-8 east after Nimitz Blvd - San Diego, CA

West End – Past Views ‐ San Diego, CA

Past Views Gallery (Tap to Expand / Collapse Section)

West

This sign bridge was removed during construction for the replacement of the West Mission Bay Drive Bridge spanning the San Diego River. Work replacing the early 1950s span ran from Summer 2018 to mid 2022. 07/13/18

Updated May 17, 2022