Interstate 405 (California)
Interstate highway in California, USA
Interstate 405 (I-405) is a major north–south auxiliary Interstate Highway in Southern California. The entire route is known as the northern segment of the San Diego Freeway. It is also known colloquially as "the 405" to Southern California residents (See also California English § Freeways). I-405 is a bypass auxiliary route of I-5, running along the southern and western parts of the Greater Los Angeles urban area from Irvine in the south to Sylmar in the north.
I-405, heavily traveled by both commuters and freight haulers along its entire length, is the third busiest freeway in the United States as measured by annual average daily traffic. It has played a crucial role in the development of dozens of cities and suburbs along its route through Los Angeles and Orange counties. It also serves Los Angeles International Airport, Long Beach Airport, and Orange County's John Wayne Airport.
Route description
The entirety of I-405 is defined in section 615 of the California Streets and Highways Code as Route 405, and that the highway is from "Route 5 near El Toro to Route 5 near San Fernando". This definition corresponds with the Federal Highway Administration (FHWA)'s route logs of I-405.
I-405 is part of the California Freeway and Expressway System and is part of 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.
Begin with the source’s own compact description: “Interstate 405 (California)” is interstate highway in California, USA. The dossier treats that line as a proposition to test through Interstate, California and highway, not as a finished interpretation.
Why this record matters
The phrase “interstate highway in California, USA” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Aug 12, 2026. The linked authority identifier is Q399983. Authority coordinates are 33.825, -118.225. 2 of 2 selected statements include explicit references; 0 carry qualifiers and 0 use preferred rank.
The absence of detail may reflect summary conventions rather than a lack of surviving documentation. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “Interstate 405 (California)”, its source revision and the description used here.
- Expand the search: follow Interstate 405 (California) primary sources, Interstate 405 (California) archive and Interstate research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “Interstate 405 (California)”?
- Which institution is responsible for the underlying evidence?
- Which cited source is closest to the event, object or claim?
Search terms from this dossier
This entry incorporates text from “Interstate 405 (California)” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.