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State Route 23

Click here for a key to the symbols used. An explanation of acronyms may be found at the bottom of the page.


Routing Routing

  1. Rte 23 Seg 1From Route 1 near Aliso Canyon to Route 101.

    Post 1964 Signage History Post 1964 Signage History

    This segment was defined in 1963 to be from "Route 1 near Aliso Canyon to Route 101 near Triunfo." In 1981, Chapter 292 changed the wording to elminate the reference to Triunfo.

    Pre 1964 Signage History Pre 1964 Signage History

    In 1934, Route 23 was signed from Jct. Route 3 (US 101A, later Route 1) near Aliso Canyon to Fillmore. It corresponds to Decker Canyon Road (on the ocean side of Mulholland) and Westlake Road (on the vally side of Mulholland). It is very winding and very twisting, and portions are slow speed for good reason. However, other than Topanga Canyon (Route 27), it is the only Los Angeles county canyon road in the Malibu area that is state maintained (the other major roads: Kanan Dume and Malibu Canyon, are both County highways, not state highways). Route 23 was LRN 155, defined in 1933.

    Status Status

    In March 2019, the CTC made the following emergency allocation: $6,700,000 Los Angeles 07-LA-23 0.0/8.4. Route 23 In and near Malibu, from Route 1 to 0.1 mile south of Country Ranch Road; also on Route 1 from Route 23 to Deer Creek Road (PM LA-59.9/Ven-2.6). The Woolsey Fire began on November 8, 2018. The fire has burned over 96,000 acres and destroyed existing wood posts, signs, guardrail, support slopes, and fire debris are collecting in the drainage systems. This project will clean fire debris, repair drainage systems, guardrail, signs, and slopes.
    (Source: March 2019 CTC Minutes, Agenda Item 2.5f.(1) Item 13)

    In November 2019, it was reported that Caltrans has completed a project to improve the surface of the roadway on Westlake Boulevard between US 101 Freeway and Carlisle Road. Crews recently installed an asphalt overlay on a winding, two-lane section of Westlake, also known as Route 23, from Potrero Road south to Carlisle. Fixing the 1.9-mile stretch of pavement was the final phase of a $5.5-million effort that started in July. The lion’s share of the work was completed over the summer when crews repaved the road between the freeway and Potrero Road. Work was originally slated to be done at night, but the City of Thousand Oaks requested that Caltrans perform work during the daytime to avoid sleep disruptions for nearby residents. The schedule change increased the cost of the project, and Caltrans announced in August that it was dropping the final 2-mile stretch on the outskirts of the city due to budget constraints. The announcement was met with displeasure from residents and local officials. Days after Caltrans announced the truncated project, the agency reversed course, saying it would be able to complete improvements on the final stretch of road after all, but that the work wouldn’t start for two months.
    (Source: TO Acorn, 11/23/2019)


  2. Rte 23 Seg 2From Route 101 in Thousand Oaks to Route 118.

    Post 1964 Signage History Post 1964 Signage History

    This segment was defined in 1963 as "Route 101 near Newbury Park to Route 118". This corresponded to the old surface routing. In 1984, Chapter 409 change the routing to better reflect the current Route 23 Freeway, by referring to "Route 101 in Thousand Oaks".

    Pre 1964 Signage History Pre 1964 Signage History

    In 1934, Route 23 was signed from Jct. Route 3 (US 101A, later Route 1) near Aliso Canyon to Fillmore. It was part of LRN 155.

    The original routing of this segment was:
    (Source: Gribblenation Blog - California State Route 23; Canyons, Surface Streets and Freeways)

    • Moorpark Road from US 101 (on Thousand Oaks Blvd) N to Tierra Rejada Road
    • Tierra Rejada Road from Moorpark Road W to Spring Road
    • Spring Road N from Tierra Rejada Road to Route 118 (Los Angeles Ave)

    Status Status

    US 101 / Route 23 Interchange (~ VEN R3.636)

    In May 2009, using money from the ARRA (Stimulus Package), Ventura County commissioners agreed to give $6.5 million to Thousand Oaks to begin the design process for the widening of the interchange of US 101 and Route 23. The Thousand Oaks City Council recently decided to loan the project money from the city’s General Fund so the process could begin this year and to reimburse the General Fund when (if?) the state funding comes through in 2010-11. In late July 2009, the city reached a cooperative agreement with the California Department of Transportation to take over the design. The proposed improvements will add one lane on US 101 in each direction between the Los Angeles/Ventura County line and Moorpark Road by widening the freeway, restriping, reconstructing the median, and realigning a portion of the center line. Soundwalls will be constructed between Hampshire Road and Conejo School Road on the northbound side and between Manzanita Lane and Hampshire Road on the southbound side. The city hopes that the design process will be completed by May 2012 at the latest and that Caltrans will be able to take back the project at that point to begin the construction process. However, the construction phase is still unfunded at this point and additional federal funds will be required to complete the work by 2016 as laid out in the preliminary schedule.

    In October 2012, it was reported that the Thousand Oaks City Council voted unanimously Oct. 9, 2012 to advance up to $17.7 million from its capital fund reserves to jump-start the estimated $42-million US 101/Route 23 interchange project, pending the granting of anticipated state and federal funds. Even with the council’s approval of the loan, work can’t begin until the state agrees to the arrangement. City and county officials have been trying unsuccessfully for years to obtain state and federal funds to pay for the interchange expansion, which would add a travel lane in each direction for drivers connecting to US 101 from Route 23 or vice versa. Thousand Oaks and VCTC tried twice before to obtain a $20-million federal Transportation Investment Generating Economic Recovery (TIGER) grant. Both applications were denied.

    On March 1, 2013, the Ventura County Transportation Commission, a body representing all 10 cities in the county, approved a critical loan repayment agreement between the City of Thousand Oaks and the state that could get the long-awaited construction effort underway by the end of 2013. The project, which is estimated to cost $42 million, would add a travel lane in each direction for drivers connecting to US 101 from Route 23 and vice versa. It’s been discussed for more than a decade but the county has been unsuccessful up until now in finding the funds to pay for it. Under the agreement, Thousand Oaks will put up $15.7 million to get the work started, money that would be repaid by 2016 from the state’s Transportation Improvement Program. The Thousand Oaks City Council voted unanimously in November 2012 to advance the money from its capital fund reserves before millions in state funding becomes available.
    (Source: TO Acorn, 3/8/13)

    In December 2013, it was reported that Caltrans planned to award the construction contract in January 2014. The roadwork will add a travel lane in each direction for drivers connecting to US 101 from Route 23 and vice versa. Sound walls will be constructed on the north side of the interchange between Hampshire and Conejo School roads and on the south side between Manzanita Lane and Hampshire. Caltrans plans to award the construction contract to Security Paving Co, Inc. of Sylmar, which submitted a $24.7-million bid in September.

    In December 2015, it was reported that a decision to redesign a sound wall along US 101 in Thousand Oaks could push back the scheduled completion date of the US 101/Route 23 interchange expansion by weeks, if not months. Started in February 2014, work to expand the juncture of two of Ventura County’s busiest freeways was originally expected to last around two years. Now it’s looking more like two-and-a-half. The original plan was to save the existing retaining walls; but once excavation began, that proved to be significantly expensive because of the grading difference. The adjustments, approved by the Thousand Oaks City Council, are waiting for the goahead from the Ventura County Transportation Commission and CalTrans before they can take place, an approval process that could take weeks or months. The sound wall in question is on the south side of US 101 along southbound Hampshire Road. The wall is being moved to provide the greatest possible reduction in freeway noise to a nearby residential area on Willow Lane, according to city report. This change saw the total cost of the expansion, now in its 21st month, swell from $33.6 million to $37.5 million, a difference of nearly $4 million.
    (Source: TO Acorn, 12/3/2015)

    In February 2016, it was reported that the City of Thousand Oaks was asking Caltrans to make good on its promise to plant new trees in the place of those removed during the expansion of the US 101 - Route 23 interchange. The state agency had planned to hold off on the proposed planting work until after drought conditions improve and the use of potable water is no longer restricted for landscape purposes. Thousand Oaks noted that the project Environmental Document identified the tree removal as a biological impact that required mitigation through installation of replacement trees based on the standards of the City of Thousand Oaks Oak Tree Ordinance. Caltrans removed at least 16 mature oak trees in accordance with project plans—and may have removed even more. No timeline for when the replacement landscaping will be planted was offered. As part of its 2015 Drought Action Plan, the state’s transportation department has been evaluating all plantings that are irrigated with potable water, including those that were promised as a condition of project approval.
    (Source: TO Acorn, 2/18/2016)

    In April 2016, it was reported that construction on the US 101/Route 23 freeway interchange in Thousand Oaks, originally slated to finish in spring 2016, was now expected to end in August. The Caltrans-led expansion of the county’s busiest interchange is in its 26th month. Work was delayed in late 2015 when engineers discovered a soundwall intended for the south side of US 101 near Hampshire Road could not be built as originally designed. The soundwall redesign increased the anticipated cost of the expansion from $33.6 million to $37.5 million in December, forcing the cash-strapped state agency to come up with an additional $4 million. The taxpayers of Thousand Oaks are still waiting to be paid back for the project by Caltrans and the Ventura County Transportation Commission. So far, the city has somewhere between $11 million and $12 million invested, or roughly 37 percent of the total expense.
    (Source: Moorpark Acorn, 4/15/2016)

    In June 2016, it was noted that the completion date had been pushed to the fall. Ramp metering system installation and drainage and irrigation work are nearing completion. About 50 percent of remaining soundwall and retaining wall construction has been completed. Over the next few months, construction activities will include profile grinding, striping work and landscaping. In response to area residents’ safety concerns, Caltrans has examined the Moorpark Road northbound on-ramp and will be adding signage and a ramp meter, which will help control the flow of traffic entering the freeway and also ease some of the merging issues drivers are facing.
    (Source: TO Acorn, 6/23/2016)

    Lane Additions - US 101 to Los Angeles Avenue (~ VEN R3.636  to VEN R11.316)

    There are plans to construct mixed-flow lanes in the median of this segment (March 2001 CTC Agenda).

    Work began in early 2006 on a $58.3 million project that will add one lane in each direction between Route 101 in Thousand Oaks and Los Angeles Avenue in Moorpark. The project was originally slated for funding in 2003 but became one of hundreds statewide to be put on hold when transportation money was diverted to other uses to help balance the state budget. As a result of that delay, an additional $14.1M for the Ventura County project was required. As of March 2007, it was estimated this widening project, now totalling $70M, will be completed in 2009. However, it finished early, completing in April 2008. The route now has an additional lane in each direction in the median, wider bridges, and new sound walls expected to significantly reduce vehicle noise in adjacent neighborhoods. Cables have been installed underneath the pavement to provide real-time traffic data to the California Department of Transportation. Traffic on Route 23, which connects the Ventura and Ronald Reagan freeways, has grown from an average of 87,000 daily vehicle trips in 1995 to more than 99,000 in 2008, according to Caltrans. The freeway's expansion will help handle a projected 35% increase in traffic over the 25 years beginning in 2008. Construction was compelted nearly 14 months ahead of the scheduled opening in Fall 2009.
    (Completion information source: Los Angeles Times)

    Naming Naming

    The segment of this route between Route 101 and Route 118 is named the "Moorpark Freeway" (~ VEN R3.636  to VEN R11.316). The first segment opened in 1971; the last segment in 1994. It was named by location.

    Military Intelligence Service Memorial HighwayThis segment has also been officially named the "Military Intelligence Service Memorial Highway" (~ VEN R3.636  to VEN R11.316). This was in honor of the Nisei Soldiers of World War II who served in units of the United States Armed Forces comprising the 100/442/MIS triad. Named by Assembly Concurrent Resolution No. 62, Chapter 115 in 1994. The other parts of the triad are two segments on Route 99.
    (Image source: Conejo Valley Guide)

    Freeway Freeway

    [SHC 253.3] Entire portion. Added to the Freeway and Expressway System in 1959.


  3. Rte 23 Seg 3From Route 118 to Route 126 near Fillmore.

    Post 1964 Signage History Post 1964 Signage History

    The routing for this is unchanged since 1963.

    In 1964, a 13.1 mi segment of Route 23 between three miles south of Tierra Rejada Road and the adopted route for the Route 126 Freeway near Fillmore was adopted. The three-mile segment south of Tierra Rejada Road superseded asection adopted in November 1962. A 1965 planning map shows this as freeway; it was never upgraded. This freeway alignment is parallel to the existing traversable highway.

    Pre 1964 Signage History Pre 1964 Signage History

    This route has been signed as Route 23 since the initial state signage of routes in 1934. It was also part of LRN 155.

    Freeway Freeway

    [SHC 253.3] Entire portion (not upgraded). Added to the Freeway and Expressway system in 1959.


Classified Landcaped Freeway Classified Landcaped Freeway

The following segments are designated as Classified Landscaped Freeway:

County Route Starting PM Ending PM
Ventura 23 R3.47 R3.90
Ventura 23 R3.90 R4.09
Ventura 23 R4.20 R6.49
Ventura 23 R6.49 R6.88

Exit Information Exit Information

Other WWW Links Other WWW Links

Statistics Statistics

Overall statistics for Route 23:

Pre-1964 Legislative Route Pre-1964 Legislative Route

It is unclear, but the first reference related to a portion of what become LRN 23 may have been in 1901, when Chapter 111 declared part of the Sonora-Mono State Road as a state highway—in particular, the portion commencing east of Sonora, at a point known as Long Barn...and running thence across the summit of the Sierra Nevada Mountains to Bridgeport. This would cover what became LRN 23 between Sonora Jct and Bridgeport. More formally, the portion that become LRN 23 was added to the state system in the 1909 First Bond Issue, running from Saugus to Bridgeport. It was extended in 1911 when Chapter 468 established the “Alpine State Highway” as:

"The certain road commencing at the Calaveras big tree grove located in Calaveras County thence running to Dorrington in said county, thence E-ly following what is known as the Big Tree and Carson Valley Turnpike to Mt. Bullion in Alpine Cty, thence along county road to Markleeville in Alpine Cty, thence along that certain road via Kirkwood, Silver Lake, Pine Grove and Irishtown to Jackson in Amador Cty, including therewith the road from Picketts in Hope Valley connecting with the Lake Tahoe Wagon Road, a state highway, at Osgood's Place in El Dorado Cty, and the road from Mt Bullion via Loupe in Alpine Cty to Junction in Mono County connecting with the Sonora and Mono State Highway is hereby declared and established a state highway and shall be designated and known as "Alpine State Highway""

It was further extended in the Second Bond Act with a reference to "an extension connecting Antelope Valley in the County of Los Angeles with the city of Los Angeles by the most direct and practical route..."

By 1935, it was codified into the state highway code as the following route:

From Los Angeles to [LRN 11] near Osgood's Place in El Dorado County, via Saugus and Antelope Valley in Los Angeles County, Bridgeport in Mono County, Loupe, Mount Bullion, Markleeville and Pickett's (in Hope Valley) in Alpine County."

It was rapidly amended by 1935 Chapter 274 to be: “From Los Angeles to [LRN 11] near Meyers Station via Antelope Valley, Independence, Bridgeport, and Markleeville” The portion from Los Angeles to Markleeville was considered primary state highway.

In 1961, Chapter 1146 clarified the description, changing "Meyers Station" to "Meyers", making the definition “Los Angeles to LRN 11 near Meyers via the vicinity of Antelope Valley, Independence, Bridgeport and Markleeville.” This routing was signed as follows:

  1. As US 6 from US 99 near Sylmar to US 395 near Inyokern. This is presently signed as Route 14. This route ran along Sierra Highway, but the LRN also applied to a planned freeway routing. At one point, portions were signed as Route 7.
  2. Cosigned as US 6/US 395 from near Inyokern to Bishop. This is presently signed as US 395.
  3. As US 395 from Bishop to the vicinity of Topaz Link near the Nevada border, where it joined Route 89.

    US 395, at this point, continued to the Nevada border as LRN 95. This is present US 395.

  4. As Route 89 from Topaz Lake to Meyers. Note that, before 1953 when the highway was constructed between US 395 and near Markleeville, the segment from Markleeville to Woodfords (Route 8/Route 88) was signed as Route 4. Upon completion of the connection to US 395 (shown on the 1953 state highway map), it became Route 89, although the Route 4 cosignage remained until 1964. Additionally, Route 89 may have been cosigned with Route 88 between Woodfords and Picketts. This is present Route 89. This was part of the "Alpine State Highway".

Acronyms and Explanations:


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