High Quality Content by WIKIPEDIA articles! Interstate 405 (I-405, and colloquially referred to as "The 405" or the four-oh-five) is a major north–south Interstate Highway in Southern California. It is a bypass of Interstate 5, running along the western and southern 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.