State Route 46 Corridor Improvement Project

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Project Background

The State Route 46 Corridor Improvement Project (Corridor Project) was initiated by the San Luis Obispo Council of Governments to improve operations on State Route 46 between Airport Road (post mile 32.2) in the City of Paso Robles to the east junction of State Routes 41 and 46 (post mile 57.8). The Corridor Project proposes to widen the existing two-lane highway to a four-lane divided expressway. The new roadway will be a four-lane, access-controlled, divided expressway. It will be constructed mostly on the existing alignment with a few sections of the new expressway on new alignments. Right-of-way will be purchased throughout the entire project. Much of the State Route 46 Corridor has been permitted and constructed at this time.

In April 2005, the California Department of Transportation (Caltrans) approved the Negative Declaration/Finding of No Significant Impact for the easternmost portion of the State Route 46 4-Lane Widening Project, which covered the conversion of 39.3 miles (Interstate 5 to Antelope Grade) in both San Luis Obispo and Kern counties to a four-lane divided expressway in both District 5 and District 6. Construction was completed between post miles 0.0 and 27.9 in Kern County. Construction of the remaining project near the town of Lost Hills (post miles 27.9 to 31.9) is expected to begin in April 2021; more information can be found on the District 6 Project Webpage.

The western portion of State Route 46 (US 101 to the Wye) was subsequently analyzed in a Final Environmental Impact Report/Finding of No Significant Impact for the State Route 46 Corridor Improvement Project, approved by Caltrans in May 2006. Construction of several sections including Union, Whitley 1, Whitley 2A, Whitley 2B, from post miles 32.2 to 50.2, has been completed.

Three additional sections remain to be constructed within District 5, the Cholame Section, the Wye Section, and the Antelope Grade Section, as discussed in more detail below.

  • Cholame Section: This section extends from post mile 49.7 to 54.7. Modifications to the design of the previously identified preferred alternative of this section recently required a Final Supplemental Environmental Impact Report/Finding of No Significant Impact. This was approved February 2020 and construction began in March 2022.
  • Wye Section: This section of the Corridor Project extends from post miles 54.0 to 57.8. This section was analyzed in the 2006 Environmental Impact Report/Finding of No Significant Impact, and Alternative 8b was selected as the preferred alternative. Construction of the Wye Section began in May 2023.
  • Antelope Grade Section: This section extends from post miles 57.3 to 60.8 in San Luis Obispo County and from post miles 0.0 to 0.4 in Kern County. Design modifications to the preferred alternative previously analyzed in the 2005 Negative Declaration/Finding of No Significant Impact are currently in the design phase, and a supplemental environmental document will be prepared for changes proposed in this section. The final environmental document has been completed in January 2024. Construction is expected to start in 2026, although the section is unfunded.


Current Proposed Project - Antelope Grade Section

Caltrans proposes to convert a 3.6-mile portion of State Route 46, known as the Antelope Grade Section, to an expressway in San Luis Obispo and Kern counties. The project would include the construction of a four-lane expressway with a 62-foot median on a new alignment that would roughly parallel the existing highway corridor to the north. The project would connect the existing four-lane expressway section in Kern County with the four-lane expressway currently under construction, the Wye Section, creating a continuous east-west corridor of four-lane expressway from Interstate 5 to U.S. Route 101.

As the lead agency, Caltrans has prepared a Subsequent Initial Study with an Environmental Assessment in accordance with the California Environmental Quality Act and the National Environmental Policy Act. This environmental document analyzes the proposed Build Alternative, the Antelope Grade North Alternative, as well as changes in the environmental setting, best management practices, minimization and mitigation measures, and laws, regulations, and guidance since the finalization of the previous environmental document for the project in 2005.


project vicinity map 



Project Benefits


The Corridor Project purpose is to minimize fatal accidents, improve safety, and reduce existing and future peak-hour congestion on State Route 46 between Paso Robles and Cholame, a critical east-west corridor connecting the Central Coast and Central Valley areas of California. State Route 46 is one of the few east-west routes connecting Interstate 5 to U.S. Highway 101 and is a designated Focus Route in the State's Interregional Transportation Strategic Plan. It primarily serves interregional and interstate traffic, although it is used daily by residents of the communities of Paso Robles, Cholame, Shandon, and Whitley Gardens. It is the major east-west route between State Route 166 to the south and State Route 156 to the north that can facilitate the movement of goods by truck.


The Corridor Project is needed due to current and predicted future traffic capacity problems as well as a higher-than-average collision rate within the Wye Section. The remaining two-lane sections of the corridor continue to experience peak-hour congestion. According to data collected in 2017, approximately 17% of the traffic volume were trucks and 60% of the trucks are 5-axle and larger. Limited passing opportunities cause traffic to back up behind slower moving vehicles along the remaining two-lane sections of the corridor and can increase the risk of collision as drivers attempt to pass and overtake slower vehicles.



  • Federal Highway Administration


Estimated Funding Breakdown

Funding for the State Route 46 Corridor Improvement Project is comprised of local, state, and federal dollars. Local funding includes the support of the San Luis Obispo Council of Governments.

Sections of the Corridor Project that have already been constructed were Prop 1B funded through the Statewide Transportation Improvement Program with a combination of Corridor Mobility Improvement Account funds, the Statewide Transportation Improvement Program – Augmentation funds, Regional Transportation Improvement Program funds and Interregional Transportation Improvement Program funds.

Both the Cholame and Wye sections are fully funded for design, right-of-way and construction. Antelope Grade is currently unfunded.

Section Estimated Construction and Support
Cholame (05-3307A) $124,500,000
Wye (05-3307C) $146,200,000
Antelope Grade (05-3307E) $134,696,000


Proposed Project Schedule

Project Sections Status
Union Completed - 2011
Whitley 1 Completed - 2014
Whitley 2A Completed - 2016
Whitley 2B Completed - 2018
Cholame* Currently in Construction

Currently in Construction

Antelope Grade^

Anticipated Construction 2026

*Fully funded for design, right-of-way, and construction
^Currently unfunded


Project Contact

Public Information Office, Caltrans District 5
Phone: (805) 549-3111

Dianna Beck, Environmental Branch Chief
Phone (805) 459-9406

Nicholas Heisdorf, Project Manager
Phone: (805) 835-6558



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Title VI Information

The California Department of Transportation (Caltrans) assures that no person shall, on the basis of race, color, or national origin, be excluded from participation in, be denied the benefits of, or be otherwise subjected to discrimination under any program or activity receiving Federal financial assistance, as required by Title VI of the Civil Rights Act of 1964, as amended, the Civil Rights Restoration Act of 1987, and Federal Executive Order 12898 (Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations).

Caltrans will make every effort to ensure nondiscrimination in all of its programs and activities, whether they are federally funded or not, and that services and benefits are fairly distributed to all people, regardless of race, color, or national origin. In addition, Caltrans will facilitate meaningful participation in the transportation planning process in a nondiscriminatory manner.

Title VI Brochures

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