Interstate 405 (California)

The Bristol exit near South Coast Plaza and Segerstrom Center for the Arts, with Saddleback in the background

I-405 begins at the El Toro Y interchange in southeastern Irvine in Orange County, splitting from its parent I-5 and inheriting that route's San Diego Freeway title; I-5 continues north as the Santa Ana Freeway. The freeway passes immediately south of the Irvine Spectrum Center mall before intersecting with State Route 133 (SR 133). It then continues through Irvine, passing north of UC Irvine and then along the northern boundary of John Wayne International Airport. After passing the airport, the freeway enters Costa Mesa and has an interchange with SR 55. It passes South Coast Plaza before a partial interchange with SR 73, which serves as a partially-tolled bypass of I-405 between Costa Mesa and Laguna Niguel.

The freeway then travels through Fountain Valley and along the edges of Westminster and Huntington Beach before entering Seal Beach, where it begins to run concurrently with SR 22. It continues along the northern edge of Seal Beach, passing between Naval Weapons Station Seal Beach and Joint Forces Training Base Los Alamitos, before SR 22 splits from I-405 and continues west while the freeway turns north. I-405 then intersects the southern end of I-605 before crossing the San Gabriel River and entering Los Angeles County.

I-405 enters Los Angeles County in the city of Long Beach. It passes to the north of California State University, Long Beach and then along the south of Long Beach Airport. The freeway then intersects with I-710 before entering Carson, where it meets I-110. It also passes near California State University, Dominguez Hills and Dignity Health Sports Park, home of Major League Soccer club LA Galaxy.

After leaving Carson, I-405 briefly enters the city of Los Angeles by passing through the Harbor Gateway, a strip of land connecting San Pedro to the rest of the city. The freeway then continues to roughly parallel the contour of the coastline as it passes through the South Bay communities of Torrance, Lawndale, Redondo Beach, Hawthorne, and El Segundo. The freeway then encounters I-105 on the southeastern corner of LAX. It passes to the east of the airport, serving it with exits at Imperial Highway and Century Boulevard.

I-405 next passes through Inglewood, coming near the site of SoFi Stadium, future home to the Los Angeles Rams of the National Football League. It then passes through Westchester and Culver City where it meets SR 90, the Marina Freeway. It serves the Los Angeles neighborhoods of Mar Vista and West Los Angeles while passing a few miles east of Santa Monica, intersecting with I-10 in the process. The freeway continues into Westwood, passing just to the west of UCLA. It then passes the Getty Center as it ascends the Sepulveda Pass through the Santa Monica Mountains.

I-405 near the interchange with the Ventura Freeway (U.S. Route 101)

After cresting the mountains, I-405 descends into the San Fernando Valley, intersecting U.S. Route 101 (US 101) in the Sherman Oaks neighborhood of Los Angeles. The freeway then continues due north through the western part of the valley, passing east of Van Nuys Airport and California State University, Northridge. It intersects SR 118 in the Mission Hills area before ending in a merge with I-5 near San Fernando.

I-405 is part of the California Freeway and Expressway System,[5] and is part of the National Highway System,[6] a network of highways that are considered essential to the country's economy, defense, and mobility by the Federal Highway Administration.[7] The freeway is known as the San Diego Freeway, and parts of it are less commonly known as the Sepulveda Freeway (after Sepulveda Boulevard).[8]

The view from the Getty Center, south of the Sepulveda Pass, looking east, south, and west. I-405 can be seen at the center.

A section of I-405 was closed over the weekend of Friday, July 15, 2011 as part of the Sepulveda Pass Improvements Project.[12] Before the closing, local radio DJs and television newscasts referred to it as "Carmageddon" and "Carpocalypse", parodying the notion of Armageddon and the Apocalypse, since it was anticipated that the closure would severely impact traffic.[13][14]

In reality, traffic was lighter than normal across a wide area. The California Department of Transportation (Caltrans) reported that fewer vehicles used the roads than usual, and those who did travel by road arrived more quickly than on a normal weekend.[15] The Metrolink commuter train system recorded its highest-ever weekend ridership since it began operating in 1991. Ridership was 50% higher than the same weekend in 2010, and 10% higher than the previous weekend ridership record, which occurred during the U2 360° Tour in June 2011.[16]

In response to jetBlue Airlines' offer of special flights between Bob Hope Airport in Burbank and Long Beach Airport, a distance of only 29 miles (47 km), for $4,[17][18] a group of cyclists did the same journey in one and a half hours, compared to two and a half hours by plane (including a drive to the airport from West Hollywood 90 minutes in advance of the flight and travel time to the end destination).[19] There was also some debate about whether the Los Angeles area could benefit from car-free weekends regularly.[15]

The Los Angeles County Metropolitan Transportation Authority had full closure of a 10-mile (16 km) stretch of I-405 on the weekend of September 29–30, 2012, while construction crews worked to demolish a portion of the Mulholland Bridge.[20]

Researchers at the University of California, Los Angeles used the closure of I-405 to study particulate matter air pollution. The researchers took air samples before, during, and after the closure. The researchers found an 83% reduction in ultrafine particles, 55% reduction in fine particle matter, and 62% less black carbon.[21]

The $1 billion Sepulveda Pass Improvements Project added a high-occupancy vehicle lane and associated changes to freeway entrances, exits, and underpasses along a 10-mile stretch through the Sepulveda Pass between I-10 and U.S. 101/Ventura Boulevard.[22] The project was completed as a design-build in contrast to the traditional design-bid-build used typically in infrastructure improvement. This section of I-405 was closed for a weekend in mid-July 2011 to demolish the Mulholland Drive Bridge, and a 10-mile (16 km) section was closed for the last weekend of September 2012.[12]

Jamzilla was the name for the I-405 closure on President's Day Weekend 2014. There were lane closures and complete closures on I-405 starting February 14 at 10 p.m. until February 18 at 6 a.m. to pave and re-stripe the northbound lanes.[23]

On May 23, 2014, the 10-mile (16 km) high-occupancy vehicle lane was opened to traffic.[24]

Proposed changes between the Manchester and Century Boulevard interchanges in the City of Inglewood are to provide a new southbound on-ramp and a new northbound off-ramp for Arbor Vitae Street, to reconstruct and widened the Arbor Vitae Street over-bridge and replace the Century Boulevard overcrossing structure.[25] This work would reduce congestion on the approach to LAX. The California Department of Transportation has not yet issued a start date for this work.

The Orange County Transportation Authority is currently preparing the design plans to add a High-occupancy toll (HOT) express lane and one mixed flow lane in each direction between SR 73 in Costa Mesa and I-605 in Seal Beach.[26] The I-405 Improvement Project is starting construction in 2018 and is scheduled to be completed in 2023.

Following the 1966 UCLA–USC rivalry football game, USC was voted into the Rose Bowl despite the UCLA team's having defeated the Trojans—with both teams having only one loss during the season. UCLA students protested by blocking the freeway's northbound lanes at Wilshire Boulevard.

While dangerous high-speed chases along the San Diego Freeway are not uncommon, perhaps the most famous chase in its history was also one of the slowest. On the afternoon of June 17, 1994, former athlete and actor O.J. Simpson, who was accused of murdering his ex-wife Nicole Brown Simpson and waiter Ron Goldman, took to the freeway in a white Ford Bronco (driven by former teammate Al Cowlings) with police in pursuit. A widely televised low-speed chase ensued and ended hours later when Simpson returned to his Brentwood, Los Angeles, home and surrendered to law enforcement.[27]

Ennis Cosby, the only son of Bill Cosby, was murdered along I-405 in Los Angeles on January 16, 1997, while fixing a flat tire.[28]

On March 10, 2019, the portion of I-405 between the Ventura Freeway (US 101) and Burbank Boulevard in the Sherman Oaks area was closed in both directions as a propane tanker truck carrying more than 9,000 US gallons (34,000 l) of flammable gas overturned along the southbound lanes of I-405. No explosion resulted from the incident.[29]