|Length:||350.34 mi[a] (563.82 km)|
|Existed:||1964 – present|
|West end:||Sunset Cliffs Boulevard / Nimitz Boulevard in San Diego, CA|
|US 95 in Yuma, AZ|
|East end:||I-10 near Casa Grande, AZ|
|Counties:||CA: San Diego, Imperial
AZ: Yuma, Maricopa, Pinal
Interstate 8 (I-8) is an Interstate Highway in the southwestern United States. It runs from the southern edge of Mission Bay at Sunset Cliffs Blvd, in San Diego, California, almost at the Pacific Ocean, to the junction with Interstate 10, just southeast of Casa Grande, Arizona. In California, the freeway travels through the San Diego metropolitan area before crossing the Cuyamaca Mountains and providing access through the Imperial Valley, including the city of El Centro. Crossing the Colorado River into Arizona, I-8 continues through the city of Yuma across the desert to Casa Grande.
The first route over the Cuyamaca Mountains was dedicated in 1912, and a plank road served as the first road across the Imperial Valley to Yuma. These were later replaced by U.S. Route 80 across California and part of Arizona, and Arizona State Route 84 between Gila Bend and Casa Grande. With the construction of the Interstate Highway System, US 80 was slowly replaced by I-8 as the latter was constructed. The route was completed in 1975 through California, and by 1977 through Arizona, though the bridge over the Colorado River was not completed until 1978.
Route description 
I-8 is part of the National Highway System, a network of roadways important to the country's economy, defense, and mobility. I-8 from the eastern junction with SR 98 to the eastern end is designated as part of the Juan Bautista de Anza National Historic Trail auto tour route, promoted by the National Park Service.
San Diego to Arizona border 
I-8 is part of the California Freeway and Expressway System and is eligible for the State Scenic Highway System from I-5 to the western junction of SR 98, though it is not an official state scenic highway. It is officially known as the Border Friendship Route from San Diego to the Arizona state line. It is also signed as the Ocean Beach Freeway west of I-5 and as the Kumeyaay Highway (after the local Native American tribe) for the entire length within San Diego County. Between Old Town San Diego and El Cajon, it is called the Mission Valley Freeway.
I-8 begins at the intersection of Sunset Cliffs Boulevard and Nimitz Boulevard. For its first few miles, it parallels the San Diego River Floodway east. Near Old Town, I-8 intersects with I-5 as well as with the former SR 209. I-8 continues eastward, bisecting the area known as "Hotel Circle." As I-8 enters Mission Valley, it has junctions with SR 163, I-805, and I-15 and its continuation, SR 15. In La Mesa, the route interchanges with SR 125. I-8 continues into El Cajon, where it intersects with SR 67 before it ascends into the mountains and the Cleveland National Forest, traveling through towns such as Alpine and Pine Valley. I-8 intersects with SR 79 in the national forest before passing through the La Posta and Campo Indian reservations. In Boulevard, I-8 has an interchange with the eastern end of SR 94.
I-8 straddles the San Diego—Imperial county line for a few miles before turning east. At the Mountain Springs/In Ko Pah grade, the freeway is routed down two separate canyons, as the freeway descends 4,000 feet (1,200 m) in 11 miles (18 km). In places, the median is over 1.5 miles (2.4 km) wide. I-8 also has the lowest above-ground elevation of any interstate at 52 feet (16 m) below sea level near El Centro, California. The route descends to the Imperial Valley, where it intersects with SR 98, a highway leading to Calexico. I-8 then goes through Coyote Wells before entering the city of El Centro several miles later.
In El Centro, I-8 intersects with SR 86 and SR 111, both north–south routes which connect to I-10 in the Coachella Valley (north of the Salton Sea). SR 115 and SR 98 end at I-8. The freeway then traverses the Imperial Sand Dunes Recreation Area and intersects with SR 186 leading to Mexico. I-8 runs parallel to the All-American Canal across the desert for roughly fifty-five miles. At points in eastern Imperial County, the border is less than 0.5 miles (0.80 km) south of the Interstate. I-8 then passes through Felicity and Winterhaven before crossing the Colorado River into Yuma, Arizona.
Yuma to Casa Grande 
I-8 enters Arizona from California at the Colorado River bridge at Yuma. It initially heads south through Yuma until the interchange with US 95 where the freeway begins to make the turn to the east. West of Wellton, the highway curves towards the north to take a northeasterly course. Through this part of Arizona, I-8 passes along the northern edge of the Barry M. Goldwater Air Force Range and to the south of the Yuma Proving Ground. It keeps a northeastern heading until it reaches Gila Bend where it intersects SR 85 which leads to Phoenix. After leaving Gila Bend, I-8 takes a southeastern heading as it passes through the Sonoran Desert National Monument. After exiting the monument, the highway continues on an easterly heading to a junction with SR 84 that will parallel I-8 to the north and go through Casa Grande while I-8 will pass to the south of the city. I-8 reaches its eastern terminus at an interchange with I-10 which continues on to Tucson.
Route 85 between I-10 and I-8, as well as I-8 between Route 85 and I-10 in Casa Grande, has been promoted as a bypass of the Phoenix area for long-distance travelers on I-10.
The I-8 designation was accepted as a chargeable Interstate by the American Association of State Highway Officials in 1957, and was designated as I-8 in 1964 by the California State Legislature; the US 80 designation was removed from the law at that time.
San Diego area 
Much of the I-8 freeway from San Diego to La Mesa was constructed between 1947 and 1950 as part of the Alvarado Canyon Freeway, a bypass of the old US 80 routing along El Cajon Boulevard and La Mesa Boulevard. Planning first began in 1932, but was delayed by the onset of World War II. Priority was given to planning US 80 in 1962 by the California Chamber of Commerce. In 1964, I-8 was officially designated by the California State Legislature, and the US 80 designation was removed. By 1965, I-8 from Fairmount Avenue to El Cajon Boulevard was one of the first freeway stretches in the county to have a center barrier installed in the median.
The "Ocean Beach Freeway" section west of I-5 was authorized as Route 286 in 1959. This was renumbered to SR 109 in the 1964 renumbering. Plans for an interchange between I-5, I-8, SR 209, and SR 109 date from 1965, although several concerns had to be taken into account, including the preservation of historical Old Town and keeping traffic through the area moving during construction. The goal was to begin construction in 1966, and complete the interchange in 1969. There were concerns about a $3 billion shortfall in funding during May 1966, which caused the San Diego Chamber of Commerce Highway Committee to recommend the completion of SR 109 as a project. This was projected to be the final highway project before I-5 was completed in San Diego County.
Construction had begun on September 22, 1966, and the interchange was to replace the intersection of Pacific Highway and Rosecrans Street. The cost of the interchange was projected to be $10.86 million. SR 109 was planned to follow Camino del Rio up to the Frontier traffic circle, where the city of San Diego would resume construction; both SR 109 and SR 209 were to be constructed in the future. The eight-lane freeway was projected to relieve traffic in the Frontier Street area coming from the San Diego Sports Arena. Bidding for the construction contract for SR 109 was to begin in 1968, after the City Council endorsed the route in December 1967. Completion of both the interchange and SR 109 was planned for early 1969. An interchange was planned at Midway Drive, and the western end of the freeway was to be at Sunset Cliffs and Nimitz boulevards. The cost of the SR 109 project was estimated to be $2.3 million.
The ramp from south I-5 to Camino del Rio opened in February 1968, and a second ramp from southbound I-5 to eastbound I-8 opened in August 1968, with the remainder of the project to be completed in summer 1969. The groundbreaking for the Ocean Beach Freeway took place on September 23, 1968, with the estimated completion to take place within 15 months. However, rain in February 1969 delayed many construction projects across the county, including the SR 109 extension. The entire project was completed in September, with the road scheduled to open in October. The routing of SR 109 was officially added to I-8 in 1972.
Cuyamaca Mountains 
In the Mountain Springs pass between San Diego and Imperial counties, the eastbound lanes traverse the pass on the former roadbed of US 80. The westbound lanes were placed on a different routing that had been constructed by November 1963. A contract for paving the 9.7 miles (15.6 km) from the San Diego–Imperial county line to SR 98, including the eastbound lanes, was given to the Isbell Construction Company for $3.69 million in the same month.
Imperial Valley 
The highway through Imperial Valley was originally a plank road made of pieces of wood that were tied together. Following this, US 80 was constructed through the valley as the main east–west route. Plans for a new freeway across the southernmost reaches of California date from before 1950. In 1957, the City of El Centro expressed a desire for the new freeway to replace US 80 to be routed along the southern limits of the city. Caltrans engineer Jacob Dekema stated at the time that the four-lane freeway would not be constructed on the US 80 routing due to possible expansion of the Naval Air Facility El Centro.
In October 1964, the portion of I-8 between Imperial Avenue in El Centro to SR 111 appeared in the state budget. Construction was underway on the stretch from Seeley to SR 111 by June 1966, and the entire portion through the county was planned for completion by 1968. This 12.2 miles (19.6 km) portion, extending west to Drew Road, was planned for completion by early 1967, at a cost of $200 million; however, the date for completion of the freeway had slipped to 1972. The state ordered the construction of the portion from west of Coyote Wells to just east of Drew Road in September 1967. The next year, Jacob Dekema indicated that the goal was to have I-8 completed by 1973, citing a deadline in order to have the federal government pay for up to ninety percent of the costs. The other freeways were to be delayed because of this.
In early 1970, the portion of the freeway from west of Ogilby Road to east of Algodones Road was under construction, and projections were to have this portion completed by later that year. This $5.2 million project also included resurfacing the freeway that had already been built through the Colorado Desert Sandhills; this part of the freeway had been constructed between 1961 and 1965. By this time, it was estimated that the drive from San Diego to El Centro now took two hours, as opposed to the 3.5 hours required two decades earlier, and the two days required in the pioneer era. This part of the freeway was opened in July 1970. The segment from SR 111 to the As I-8 was constructed through the valley, the freeway caused a break in many north-south roads where access to the part of the road on the other side of the freeway was cut off. Plans were put in place to construct frontage roads to improve access through the region.
The 16 miles (26 km) portion of I-8 bypassing Holtville began construction in December 1969, and was nearing completion in May 1971, which resulted in a continuous freeway that connected two existing segments from Crestwood in San Diego County to just west of Winterhaven. It was estimated that the bypass would save travelers 20 minutes of travel time through the Imperial Valley. The cost of this project was $11.2 million. However, Holtville residents raised concerns about SR 115 providing the only access to the eastern part of the city, notably the narrow and curved portion leading from the freeway into town. Construction on this portion began at 3:30 a.m. daily during the summer in order to avoid the desert heat. In addition to this, construction of the Highline Canal overpass involved a 120 feet (37 m) steel span that was prefabricated and made of girders that were hoisted into position by barges. The Matich Construction Company attempted to set the world record for laying the most concrete in a day, aided by the level terrain, but failed to do so after the concrete mixer malfunctioned. That same year, bids for an Arizona plant inspection station near Winterhaven, next to the California agricultural inspection station, were submitted.
The last 6.5 miles (10.5 km) part of the California portion, from near Algodones Road to west of the Arizona state line, was to enter the bidding phase in early 1972. I-8 was scheduled to be completed in the summer of 1975 between San Diego and Yuma, although there would be a break in the freeway around Yuma; this occurred by October 1975. At the time the California portion was completed, it was the preferred route to Phoenix from some areas of Los Angeles, since I-10 had not been completed.
The missing portion of the highway was the new bridge over the Colorado River, which was constructed at a cost of $7.4 million. In June 1975, there were concerns regarding the state delaying new construction projects due to financial concerns, and the effects this would have on the bridge. The bid for the project was awarded to Novo-Rados Construction in October 1975, as one of the final projects before the construction freeze. The new bridge, which replaced the old US 80 bridge, was dedicated on August 18, 1978; this completed I-8 from San Diego to Casa Grande. The Arizona Department of Transportation and the City of Yuma assisted in the planning process. By the time the California portion of the freeway was complete, the average cost was $1 million per mile. The bridge opened on September 20, 1978. The State of California was responsible for the bridge construction, even though the State of Arizona owned half of the bridge.
Between Yuma and Gila Bend, I-8 runs alongside the routes of both the Gila Trail and the Butterfield Overland Mail Company line. This portion of the route of I-8 was originally part of the proposed state system of highway in 1921. By 1926, this section became part of the cross-country highway US 80. The route was not paved at this time, but was a gravel road along the entire corridor. By 1928, the portion of I-8 between Gila Bend and Casa Grande was designated as SR 84. By 1929, a small portion of the highway was paved near Yuma and SR 84 was under construction. SR 84 was completed by 1930, but not paved and the segment of US 80 between Astec and Sentinel had been paved. By 1931, the entire portion of the highway under the US 80 designation had been paved. Paving of the SR 84 had commenced by 1934, with the portion of the highway in Maricopa County being paved. By 1935, the entire future corridor of I-8 had been paved from Yuma to Casa Grande. Drivers were told to bring spare fan belts, radiator hoses, and additional drinking water for the journey traversing the desert.
With the coming of the Interstate Highways, the corridor was to be upgraded to Interstate standards. By 1963, this process was in progress with portions of the highway between Mohawk and Gila Bend, and between Gila Bend and Stanfield upgraded. By 1971, I-8 was nearly complete including a new alignment east of Yuma built parallel and to the south of the original US 80 alignment. A new alignment was also built to the south of the SR 84 alignment at the eastern end of the highway from southwest of Stanfield to the eastern terminus at I-10 southeast of Casa Grande. The only portions of I-8 not completed at this time were the Casa Grande bypass and the western end near Yuma. As the Interstate was completed, the highways that it replaced were removed from the state highway system. In 1973, the SR 84 designation was removed from the highway from Gila Bend to the split where I-8 followed a new alignment southwest of Stanfield. In 1977, the US 80 designation was removed from this stretch in favor of I-8.
Auxiliary routes 
There are no three-digit Interstates that are related to I-8. However, there are five business routes related to I-8 that provide additional access to the towns or cities of El Cajon, Alpine, El Centro, Yuma, and Gila Bend. 
Exit list 
||San Diego||0.00||0.00||Nimitz Boulevard, Sunset Cliffs Boulevard – Mission Bay Park||At-grade intersection|
|0.50||0.80||1||Mission Bay Drive, Sports Arena Boulevard to I-5 south||Westbound exit and eastbound entrance|
|1.67||2.69||2||I-5 south (San Diego Freeway) – Downtown San Diego||No access from I-8 west to I-5 south and I-5 north to I-8 east|
|1.67||2.69||2A||I-5 north (San Diego Freeway) – Los Angeles||Westbound exit and eastbound entrance; no access from I-8 east to I-5 north and I-5 south to I-8 west|
|1.67||2.69||2B||Rosecrans Street||Westbound exit and eastbound entrance; former SR 209 south|
|2.03||3.27||2C||Morena Boulevard||Westbound exit and eastbound entrance|
|2.60||4.18||3||Taylor Street, Hotel Circle|
|3.88||6.24||4A||Hotel Circle||Westbound exit is via exit 3|
|4.06||6.53||4||SR 163 (Cabrillo Freeway) – Escondido, Downtown San Diego|
|4.69||7.55||5||Mission Center Road, Auto Circle|
|5.55||8.93||6A||Texas Street, Qualcomm Way|
|6.03||9.70||6B||I-805 (Jacob Dekema Freeway) – Los Angeles, National City, Chula Vista|
|7||I-15 (Escondido Freeway) / SR 15 – Riverside||Signed as exits 7A (north) and 7B (south) eastbound, 7A (south) and 7B (north) westbound|
|7.94||12.78||8||Mission Gorge Road, Fairmount Avenue||Eastbound exit is part of exit 7|
|La Mesa||11.24||18.09||11||Lake Murray Boulevard, 70th Street|
|12.22||19.67||12||Fletcher Parkway, Baltimore Drive|
|10.97||17.65||13A||Spring Street – Downtown La Mesa||No westbound exit|
|12.22||19.67||13A||El Cajon Boulevard||Westbound exit and eastbound entrance; former I-8 Bus. west; former US 80 west|
|13.41||21.58||13B||Jackson Drive, Grossmont Boulevard||No eastbound entrance|
|14.05||22.61||14A||La Mesa Boulevard, Grossmont Center Drive||Signed as exit 14B westbound|
|14.20||22.85||14B||SR 125 to SR 94||Signed as exit 14A westbound|
|14.30||23.01||14C||Severin Drive, Fuerte Drive|
|El Cajon||15.31||24.64||15||El Cajon Boulevard (I-8 Bus. east)||Eastbound exit and westbound entrance; former US 80 east|
|16.95||27.28||17A||Johnson Avenue||Eastbound exit and westbound entrance|
|17.45||28.08||17||SR 67 north / Magnolia Avenue – Santee, Lakeside, Ramona||Signed as exits 17B (SR 67) and 17C (Magnolia Avenue) eastbound|
|19.01||30.59||19||2nd Street||Former SR 54 west|
|20.38||32.80||20A||East Main Street (I-8 Bus. west)||Westbound exit and eastbound entrance|
|20.40||32.83||20B||Greenfield Drive – Crest||Signed as exit 20 eastbound|
|21.69||34.91||22||Los Coches Road – Lakeside|
|23.47||37.77||23||Lake Jennings Park Road|
|27.34||44.00||27||Dunbar Lane – Harbison Canyon|
|30.11||48.46||30||Tavern Road (I-8 Bus. east) – Alpine|
|32.99||53.09||33||Willows Road, Alpine Boulevard (I-8 Bus. west) – Alpine|
|35.98||57.90||36||East Willows Road|
|39.48||63.54||40||SR 79 north (Japatul Valley Road) – Descanso, Julian|
|45.18||72.71||45||Pine Valley, Julian|
|46.58||74.96||47||Sunrise Highway (CR S1)|
|50.49||81.26||51||Buckman Springs Road|
|53.63||86.31||54||Kitchen Creek Road – Cameron Station|
|60.50||97.37||61||Crestwood Road – Live Oak Springs|
|65.25||105.01||65||SR 94 west – Campo, Boulevard|
|76.93||123.81||77||In-Ko-Pah Park Road|
||80.21||129.09||80||Mountain Springs Road|
|87.13||140.22||87||SR 98 east – Calexico||Eastbound exit and westbound entrance|
|Ocotillo||87.13||140.22||89||Imperial Highway (CR S2) – Ocotillo|
|107.05||172.28||107||Drew Road (CR S29) – Seeley|
|111.11||178.81||111||Forrester Road (CR S30)|
|El Centro||114.09||183.61||114||Imperial Avenue (I-8 Bus. east) – El Centro|
|115.09||185.22||115||SR 86 (4th Street, I-8 Bus. west) – Heber, El Centro||Former US 99|
|116.08||186.81||116||Dogwood Road (CR S31)|
|118.06||190.00||118||SR 111 – Brawley, Indio, Calexico||Signed as exits 118A (south) and 118B (north)|
|124.90||201.01||125||SR 7 south / Orchard Road (CR S32)|
|127.61||205.37||128||Bonds Corner Road||Former SR 115|
|130.62||210.21||131||SR 115 (Van Der Linden Road) – Holtville||Former US 80|
|142.87||229.93||143||SR 98 west – Calexico|
|145.95||234.88||146||Brock Research Center Road|
|155.82||250.77||156||Grays Well Road|
|158.81||255.58||159||Ogilby Road (CR S34)|
|165.73||266.72||166||SR 186 south (Algodones Road) – Andrade, Mexico|
|169.97||273.54||170||Winterhaven Drive (CR S24, I-8 Bus. east) – Winterhaven|
|171.54||276.07||172||Winterhaven Drive, Fourth Avenue (I-8 Bus. west) – Winterhaven|
|California–Arizona state line|
||Yuma||0.59||0.95||1||Redondo Center Drive, Giss Parkway|
|2.23||3.59||2||US 95 (16th Street) – San Luis, Quartzsite, Yuma Proving Grounds|
|3.98||6.41||3||SR 280 south (Avenue 3E) – Yuma International Airport, Marine Corps Air Station Yuma, Yuma County Fairgrounds|
|7.66||12.33||7||Araby Road – Arizona Western College|
|9.44||15.19||9||I-8 Bus. (Avenue 8½E)|
|30.84||49.63||30||Avenue 29E – Wellton|
|37.99||61.14||37||Avenue 36E – Roll|
|42.10||67.75||42||Avenue 40E – Tacna|
|54.98||88.48||54||Avenue 52E – Mohawk Valley|
||87.10||140.17||87||Sentinel, Hyder, Agua Caliente|
|102.34||164.70||102||Painted Rock Road|
|111.49||179.43||111||Citrus Valley Road|
|Gila Bend||115.68||186.17||116||I-8 Bus. east / SR 85 – Phoenix, Ajo|
|119.47||192.27||119||I-8 Bus. west (Butterfield Trail) to SR 85 north / I-10|
|144.60||232.71||144||Vekol Valley Road|
||151.73||244.19||151||SR 84 east to SR 347 north – Maricopa|
|172.62||277.80||172||Thornton Road – Casa Grande|
|174.62||281.02||174||Trekell Road – Casa Grande|
|Casa Grande||178.36||287.04||178||I-10 – Phoenix, Tucson||Eastbound exit and westbound entrance; signed as exits 178A (west) and 178B (east)|
See also 
- Total mileage is a summation of the two state mileages.
- "Southern California". National Highway System. Federal Highway Administration. Retrieved September 29, 2012.
- "Arizona". National Highway System. Federal Highway Administration. Retrieved September 29, 2012.
- Adderly, Kevin (August 26, 2010). "The National Highway System". Planning, Environment, and Realty. Federal Highway Administration. Retrieved January 1, 2011.
- "Juan Bautista de Anza National Historic Trail Guide: Imperial County". National Park Service. Retrieved 6 October 2008.
- "Juan Bautista de Anza National Historic Trail Guide: Yuma County". National Park Service. Retrieved October 6, 2008.
- "Juan Bautista de Anza National Historic Trail Guide: Maricopa County". National Park Service. Retrieved October 6, 2008.
- "Juan Bautista de Anza National Historic Trail Guide: Pinal County". National Park Service. Retrieved October 6, 2008.
- California Assembly. "Sections 250–257". Streets and Highway Code. Legislative Counsel of California. Retrieved November 27, 2011.
- California Assembly. "Sections 260–284". Streets and Highway Code. Legislative Counsel of California. Retrieved November 27, 2011.
- Cadd, Dennis (February 13, 2012). "Officially Designated Scenic Highways". Scenic Highway Program. California Department of Transportation. Retrieved March 7, 2012.
- Staff (January 2009). 2008 Named Freeways, Highways, Structures and Other Appurtenances in California (PDF). California Department of Transportation. p. 159. Retrieved March 7, 2012.
- Thomas Brothers Maps (2000). California Road Atlas and Driver's Guide (Map). pp. 107, 111, 112, 212, 213, 214, V. ISBN 978-1-58174-110-0.
- Rand McNally (2008). The Road Atlas: United States, Canada, and Mexico (Map). pp. 15,17. ISBN 978-0-528-93961-7.
- Acme Maps. Acme Mapper (Map). Cartography by Google, Inc.. http://mapper.acme.com/?ll=32.69646,-116.08944&z=13&t=T&marker0=41.19886%2C-120.94414. Retrieved April 28, 2013.
- Staff (29 February 2012). "Previous Interstate Facts of the Day". Celebrating the Eisenhower Interstate Highway System. Federal Highway Administration. Retrieved 29 September 2012.
- Pittman, p. 341.
- Staff (December 31, 2006). "2006 ADOT Highway Log" (PDF). Arizona Department of Transportation. pp. 1–8. Archived from the original on March 26, 2009. Retrieved April 11, 2008.
- Google Inc. Google Maps – Overview Map of I-8 in Arizona (Map). Cartography by Google, Inc. http://maps.google.com/maps?f=d&hl=en&geocode=12292208217460437544,32.728310,-114.617480%3B401209425362210788,32.817011,-111.683029&saddr=I-8+E+%4032.728310,+-114.617480&daddr=Exit+178A+%4032.817011,+-111.683029&doflg=ptm&sll=32.795685,-113.150255&sspn=3.181171,5.119629&ie=UTF8&z=8. Retrieved April 11, 2008.
- Staff. Exit 200 eastbound overhead (Highway guide sign). Casa Grande, AZ: Arizona Department of Transportation. http://commons.wikimedia.org/wiki/File:Interstate_8_Eastern_Terminus.jpg. Retrieved October 27, 2012.
- Public Roads Administration (August 14, 1957). Official Route Numbering for the National System of Interstate and Defense Highways (Map). Cartography by American Association of State Highway Officials. http://commons.wikimedia.org/wiki/File:Interstate_Highway_plan_August_14,_1957.jpg. Retrieved April 4, 2012.
- "Route Renumbering: New Green Markers Will Replaces Old Shields" (PDF). California Highways and Public Works 43 (1–2): 11–14. March–April 1964. ISSN 0008-1159. Retrieved March 8, 2012.
- California State Legislature (1963). "An act...relating to routes on the state highway system". State of California. 1963 chapter 385.
- Yates, Eric (February 6, 2011). "Alvarado Canyon Highway: La Mesa’s First Free-Way Speeds City into Modern Era in 1950". La Mesa Patch.
- Staff (August 23, 1962). "State C of C Urges New Roads in Area". The San Diego Union. p. C17.
- Brooks, Joe (January 7, 1965). "More Freeway Center Barriers Are Planned". The San Diego Union. p. A21.
- California State Legislature (1959). "An act to amend...the Streets and Highways Code, relating to state highways, providing for a California Freeway and Expressway System...". State of California. 1959 chapter 1062.
- Staff (March 16, 1965). "$11 Million Interchange Projected". The San Diego Union. p. A15.
- Staff (May 11, 1966). "Fund Loss Feared For State Highways Under Transit Plan". The San Diego Union. p. A22.
- James, Paul (August 1, 1966). "Interstate 5 Will Have 36 Interchanges For Easy Travel". The San Diego Union. p. B1.
- Brown, Joe (March 26, 1967). "'Stack' Like Plate Of Spaghetti". The San Diego Union. p. B1.
- Staff (December 4, 1966). "$11 Million Interchange To Link Freeways". The San Diego Union. p. B4.
- Staff (February 27, 1968). "Interstate 5 and 8 Ramps to Close". The San Diego Union. p. C1.
- Staff (December 29, 1967). "Council Approves 109 Freeway Route". The San Diego Union. p. B3.
- Staff (September 24, 1968). "Ground Broken For Beach Freeway". The San Diego Union. p. C3.
- Staff (August 3, 1968). "Interstate 5-8 Revisions Due On Monday". The San Diego Union. p. B1.
- Clance, Homer (February 25, 1969). "2,000 To 3,000 Building Men Idled By Rain". The San Diego Union. p. B8.
- Scarr, Lew (September 26, 1969). "Dedication Of Ocean Beach Freeway Slated". The San Diego Union. p. B1.
- California State Legislature (1972). "An act to amend...the Streets and Highways Code, relating to state highways". State of California. 1972 chapter 1216.
- McVicar, Jim (May 19, 1970). "San Diego-Yuma Freeway Dream Nearing Fruition". The San Diego Union. p. B3.
- Staff (November 13, 1963). "State Reviews Low Road Bid For U.S. 80". The San Diego Union. p. A17.
- Staff (February 22, 1965). "San Diego County Freeway System". The San Diego Union. p. A3.
- California Division of Highways (1936). Road Map of California (Map). http://www.cosmos-monitor.com/ca/map1936/san-diego-orange-imperial.html.
- Staff (August 22, 1966). "Completion Of Freeway Link Nears". The San Diego Union. p. B3.
- Staff (March 28, 1957). "Highway 80 Relocation Outlined". Los Angeles Times. p. B8.
- Staff (October 30, 1964). "$42 Million OKd for County Roads". The San Diego Union. p. A2. OCLC 13155544.
- Staff (June 19, 1966). "High Of 110 Predicted For Today". The San Diego Union. p. A30.
- Staff (September 2, 1967). "Rains Cause Flooding, Power Loss". The San Diego Union. p. B3.
- Hudson, Ken (April 5, 1968). "Freeway 8 To Yuma Seen By '73". The San Diego Union. p. B3.
- California Division of Highways (1961). California State Highway Map (Map). http://www.cosmos-monitor.com/ca/map1961/south.html.
- Shell Oil Company (1965). California (Map). Section W6.
- Staff (July 13, 1970). "Interstate 8 Link Ready". The San Diego Union. p. B1.
- MacMillan, Doug (July 24, 1970). "Interstate 8 Link Due By Next May". The San Diego Union (Imperial Valley ed.). p. B1.
- Ruane, Richard (February 21, 1971). "1,200 Miles Of County's Roads Paved". The San Diego Union (Imperial Valley ed.). p. B1.
- Staff (May 18, 1971). "Final Work Being Done On Freeway". The San Diego Union (Imperial Valley ed.). p. B1.
- MacMillan, Doug (April 29, 1971). "Interstate 8 Link To Open Near Holtville Next Month". The San Diego Union (Imperial Valley ed.). p. B1.
- Staff (September 18, 1970). "El Centro Firm's Bid Low For Inspection Station". The San Diego Union (Imperial Valley ed.). p. B1.
- Staff (December 15, 1971). "Vegetable Shipments Up". The San Diego Union (Imperial Valley ed.). p. B1.
- Staff (June 19, 1975). "State Orders Halt In New Road Projects". The San Diego Union. p. B1.
- Staff (October 4, 1975). "$14.9 Million Road Project Awarded To Daley Corp.". The San Diego Union. p. B5.
- Staff (September 21, 1978). "Yuma I-8 Bridge Opens". The San Diego Union. p. B4.
- Trimble, p. 399.
- Arizona Highway Department (1921). Tentative 7% System (Map). http://www.aaroads.com/west/maps/1921-az.html. Retrieved May 4, 2008.
- Arizona Highway Department (1926). Map of Arizona (Map). http://www.aaroads.com/west/maps/1926-az.html. Retrieved May 3, 2008.
- Staff (February 7, 1928). "Resolution 1928-P-144". Right-of-Way Resolutions. Arizona Department of Transportation. Retrieved May 4, 2008.
- Arizona Highway Department (1929). Map of Arizona (Map). http://www.aaroads.com/west/maps/1929-az.html. Retrieved May 4, 2008.
- Arizona Highway Department (1930). Condition Map of State Highway System (Map). http://www.aaroads.com/west/maps/1930-az.html. Retrieved May 4, 2008.
- Arizona Highway Department (1931). Condition Map of State Highway System (Map). http://www.aaroads.com/west/maps/1931-az.html. Retrieved May 5, 2008.
- Arizona Highway Department (1934). Condition Map of State Highway System (Map). http://www.aaroads.com/west/maps/1934-az.html. Retrieved May 4, 2008.
- Arizona Highway Department (1935). Road Map of Arizona (Map). Cartography by H.M. DeMerse. http://www.arizonaroads.com/maps/index.html. Retrieved May 4, 2008.
- Trimble, p. 154.
- Arizona Highway Department (1963). Road Map of Arizona (Map). 1 in:24 mi. Cartography by Rand McNally. http://www.aaroads.com/west/maps/1963-az.html. Retrieved May 4, 2008.
- Arizona Highway Department (1971). Road Map of Arizona (Map). Cartography by Photogrammetry and Mapping Division. http://www.aaroads.com/west/maps/1971-az.html. Retrieved May 4, 2008.
- Staff (September 21, 1973). "Resolution 1973-20-075". Right-of-Way Resolutions. Arizona Department of Transportation. Retrieved May 4, 2008.
- Staff (September 16, 1977). "Resolution 1977-16-A-048". Right-of-Way Resolutions. Arizona Department of Transportation. Retrieved May 4, 2008.
- Staff (January 9, 2008). "Interstate 8 Freeway Interchanges" (PDF). California Numbered Exit Uniform System. California Department of Transportation. Retrieved February 5, 2009.
Works cited 
|Wikimedia Commons has media related to: Interstate 8|
- Interstate 8 at California Highways
- Interstate 8 at the Interstate Guide
- Interstate 8 in California and Arizona at AA Roads
- Old SR 209 and the Cabrillo National Monument at Floodgap Roadgap