Interstate 805

Interstate 805 (I-805) is a major north–south auxiliary Interstate Highway in Southern California. It is a bypass auxiliary route of I-5, running roughly through the center of the Greater San Diego region from San Ysidro (part of the city of San Diego) near the Mexico–U.S. border to near Del Mar. The southern terminus of I-805 at I-5 in San Ysidro is less than 1 mi (1.6 km) north of the Mexican border. I-805 then traverses the cities of Chula Vista and National City before reentering San Diego. The freeway passes through the San Diego neighborhoods of North Park, Mission Valley, Clairemont, and University City before terminating at I-5 in the Sorrento Valley neighborhood near the Del Mar city limit.

Planning for I-805 began in 1956, and the route was officially designated in 1959 before it was renumbered in the 1964 state highway renumbering. Starting in 1967, the freeway was built in phases, with the northern part of the freeway finished before the southern part. I-805 was completed and open to traffic in 1975. Named the Jacob Dekema Freeway after the longtime head of the regional division of the California Department of Transportation (Caltrans), I-805 has been frequently cited for its complex engineering and architecture, including near I-8 on the Mission Valley Viaduct. Since then, several construction projects have taken place, including the construction of carpool lanes.

The entirety of I-805 is defined in section 621 of the California Streets and Highways Code as Route 805, and that the highway is from "Route 5 near San Ysidro to Route 5 north of La Jolla and easterly of existing Route 5". This definition roughly corresponds with the Federal Highway Administration (FHWA)'s route logs of I-805.

I-805 begins at I-5 near the Mexican border in a far south part of San Ysidro, a neighborhood of San Diego. As it starts its journey northwards, it quickly has a junction with State Route 905 (SR 905) before exiting the city of San Diego and entering Chula Vista. Within the past 20 years the freeway has delineated the apparent divide between rich and poor in the city of Chula Vista; those on the eastern side of the freeway have been more affluent and have better schools compared to those on the western side. Just outside the city, I-805 meets County Route S17 (CR S17), also named Bonita Road, before coming to an interchange with SR 54. The freeway then enters National City, where it intersects Sweetwater Road and Plaza Boulevard, before leaving the city and reentering the city of San Diego.

I-805 continues northward through San Diego, where it intersects SR 94, the Martin Luther King Jr. Freeway. As the freeway continues through San Diego, it meets SR 15, the continuation of I-15. It then intersects El Cajon Boulevard before passing under the Hazard Memorial Bridge that carries Adams Avenue. The bridge was named after Roscoe Hazard for his involvement in the construction of several roads and highways in Southern California. I-805 then travels on the Mission Valley Viaduct, a towering reinforced concrete viaduct built in 1972, spanning over Mission Valley and the San Diego River. The viaduct is the top stack of the Jack Schrade Interchange over I-8, which runs along the south side of Mission Valley and crosses underneath the viaduct perpendicularly, and is San Diego County's only symmetrical stack interchange. The San Diego Trolley traffic also runs under the viaduct on the valley floor.

After intersecting SR 163, also known as the Cabrillo Freeway, I-805 continues through suburban San Diego, where it meets SR 52 in Clairemont Mesa. North of SR 52, it closely parallels I-5 near La Jolla, heading northwest. Passing under the Eastgate Mall arch bridge and entering Sorrento Valley, it finally meets its north end at I-5. During the widening project which was completed in 2007, I-5 at the I-805 merge was built to be 21 lanes wide. Eastbound SR 56 and Carmel Mountain Road are accessible via a parallel carriageway for local traffic heading northbound from I-805; traffic from SR 56 westbound can merge onto I-805 from the local bypass.

The route is officially known as the Jacob Dekema Freeway after Jacob Dekema, a pioneering force from the California Department of Transportation (Caltrans) who helped shape the San Diego freeway system. It is also part of the California Freeway and Expressway System and the National Highway System, a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration. In 2013, I-805 had an annual average daily traffic (AADT) of 41,500 at the southern terminus, and 262,000 between Bonita Road and SR 54, the latter of which was the highest AADT for the highway.

According to Dekema, planning for I-805 began in 1956. The original routing for I-805 was approved as an Interstate Highway in July 1958. It was added to the state highway system and the Freeway and Expressway System in 1959 as Route 241. I-805 was expected to reduce traffic on what was then US 101 between Los Angeles and San Diego, when the former was opened. Route 241 was renumbered to Route 805 in the 1964 state highway renumbering, and I-5 was designated along the route from Los Angeles to San Diego. Further planning was underway in 1965, with the goal to have the route built by 1972, the federal highway funding deadline. This was to be the first freeway in the area with no prior road along its route that it would replace; the goal was to provide a bypass around San Diego for those traveling to Mexico, and improve access for local residents. By June, houses along the route in the North Park area were being sold, as the land was needed for the first stretch of the freeway to be constructed. The next year, Dekema confirmed that the first portion of what was known as the Inland Freeway to be built would be between Home and Adams avenues.