<P> Interstate 405 (usually pronounced four - oh - five), also known as I - 405 or colloquially as "the 405", is a major north--south Interstate Highway in Southern California . It is a bypass auxiliary route of Interstate 5, running along the southern and western parts of the Greater Los Angeles Area from Irvine in the south to near San Fernando in the north . The entire route is known as the northern segment of the San Diego Freeway . It goes past Los Angeles International Airport (LAX). </P> <P> I - 405 is a heavily traveled thoroughfare by both commuters and by freight haulers along its entire length and is the busiest and most congested freeway in the United States . The freeway's annual average daily traffic between exits 21 and 22 in Seal Beach reached 374,000 in 2008, making it the highest count in the nation . It has played a crucial role in the development of dozens of cities and suburbs along its route through Los Angeles and Orange counties . </P> <P> Interstate 405 begins at the El Toro Y interchange with Interstate 5 in southeastern Irvine . It then runs northwest through Orange County to Long Beach in Los Angeles County . The freeway then roughly follows the outline of the Pacific coast, varying between five and ten miles (16 km) inland before crossing over the Sepulveda Pass in the Santa Monica Mountains . I - 405 next travels northerly through the San Fernando Valley, before its termination with I - 5 in the Mission Hills district of Los Angeles . Large portions of the route closely parallel Sepulveda Boulevard . </P> <P> The freeway's congestion problems are legendary, leading to jokes that the road was numbered 405 because traffic moves at "four or five" miles per hour, or because drivers need "four or five" hours to get anywhere . Indeed, average speeds as low as 5 mph are routinely recorded during morning and afternoon commutes, and its interchanges with the Ventura Freeway (U.S. Route 101) and with the Santa Monica Freeway (Interstate 10) each consistently rank among the five most congested freeway interchanges in the United States . As a result of these congestion problems, it may take longer to pass through the entire Los Angeles area using this bypass route instead of merely taking the primary route I - 5 through Downtown . </P>

Where does the 405 freeway start and end
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