The San Diego Freeway (Interstate 405, and the part of Interstate 5 south of the El Toro Y) is one of the principal north-south highways in Southern California, and the major beltway of I-5 running through Southern California. Connecting Los Angeles to South Orange County, it is heavily traveled by commuters and freight haulers along its entire length and is known as one of the busiest and most congested freeways in the world. It has played a crucial role in the development of dozens of cities and suburbs along its route through the Greater Los Angeles area.

Route

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The San Diego Freeway splits away from the Golden State Freeway (Interstate 5) in the Mission Hills district of Los Angeles (Exits 73/158), becoming Interstate 405. From the northern San Fernando Valley it heads straight south toward the Santa Monica Mountains. After crossing over the Sepulveda Pass, its route roughly follows the outline of the Pacific coast, but between five and ten miles inland. It crosses the Los Angeles/Orange county line in Long Beach, then continues southeast through Orange County. It is joined by the Santa Ana Freeway (Interstate 5) in southeastern Irvine at the massive El Toro Y interchange, below which it merges back into Interstate 5 (at Exit 94).

The San Diego Freeway (now Interstate 5) turns due south in Mission Viejo and continues in that direction until it reaches the bluffs overlooking the Pacific Ocean in Dana Point, at which point it once again turns southeastward to follow the contour of the shoreline. After passing through the 28 miles of Marine Corps Base Camp Pendleton in northern San Diego County, it travels through the wealthy northern suburbs of San Diego and into the city itself. In the Sorrento Valley district, the freeway ends, splitting into the unnamed final portion of I-5 and the Jacob Dekema Freeway (Interstate 805).

The San Diego Freeway's congestion problems are legendary, leading to the joke that the Interstate was named 405 because traffic moves at "four or five" miles an hour. Indeed, average speeds as low as five miles per hour are routinely recorded during morning and afternoon commutes, and its interchanges with the Ventura Freeway (milepost 63) and with the Santa Monica Freeway (milepost 53) each consistently rank among the five most congested freeway interchanges in the United States. Commuters are known to despise the freeway: Steve Harvey of the Los Angeles Times once featured a personalized license plate with the text HATE405 in his column. While much of this gridlock has to do with the lack of alternate routes between many of the areas it connects (some of which, such as the Pacific Coast and Laurel Canyon freeways, were proposed but abandoned for political reasons), the freeway would likely be busy even with the addition of other roads and mass transit solutions, as it connects so many important locations in the Greater Los Angeles area.

Landmarks

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Transportation

• LAX
• Long Beach Municipal Airport
• John Wayne Airport
• Port of Los Angeles
• Port of Long Beach

Commerce/Recreation

• Century City high-rise office park
• Marina del Rey
• More than ten California state beaches, as well as many owned by counties and municipalities, and many tourist-heavy beach cities

Education and cultural

• California State University, Northridge
• The J. Paul Getty Center
• University of California, Los Angeles
• Loyola Marymount University
• California State University, Dominguez Hills
• California State University, Long Beach
• University of California, Irvine
• University of California, San Diego

Communities served

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Communities along the route of the San Diego Freeway include