Planning for proposed 4-lane State Route 239 between Brentwood and Tracy moves forward

Proposed State Route 239 Alternative A alignment. Source: Caltrans/CCTA

Public input requested; legislatively designated for over 62 years

The proposed State Route 239 Project will provide a new, four-lane highway from State Route 4 at Marsh Creek Road in Contra Costa County to Interstate 580 in Alameda County or Interstate 205 in San Joaquin County. This new state route will ultimately improve the transportation network for an area that has few viable north-south roadway connections in this approximately 17-mile stretch between eastern Contra Costa and the Central Valley.

This project is sponsored by the Contra Costa County Transportation Authority (CCTA) in partnership with Contra Costa County and the California Department of Transportation (Caltrans) – District 4. The proposed State Route 239 Project is critical to the region and needed to provide relief from increasing commute traffic through the town of Byron, enhance mobility in eastern Contra Costa, and improve access to the Byron Airport.

Source: Caltrans/CCTA

Brief History

State Route 239 has been a legislatively designated route since 1959. In 2005, Contra Costa County secured federal funds to initiate a feasibility study and a project initiation document (PID). The PID was completed in 2015 and the environmental study phase has been initiated.

Why Now?

Supporting the growing communities of eastern Contra Costa County and providing mobility options for the area are two key reasons to implement this corridor. It will serve as an important backbone for the region while helping people who live and work in eastern Contra Costa County (including Pittsburg, Antioch, Brentwood, Oakley, Byron, and Discovery Bay) and western San Joaquin County (including Tracy and Mountain House) connect, move and prosper.

Proposed State Route 239 Alternative B alignment. Source: Caltrans/CCTA


During the study phase of this project, which occurred between the spring of 2012 and the winter of 2013, a variety of stakeholder meetings were held, and several important themes emerged, including consideration of how a new route in eastern Contra Costa might affect conservation areas, agricultural lands, bird flight paths, and growth in the area. These considerations are still important, today and have set the stage for continued outreach during future project development phases.

Proposed State Route 239 cross section. Source: Caltrans/CCTA

Environmental Phase

Caltrans and CCTA are currently engaged in the environmental phase of the project development process for the State Route 239 Project. During this phase, the team will study and analyze all environmental impacts for the project area and will prepare a Draft Environmental Impact Report/ Environmental Impact Statement (EIR/EIS) for public review and comment in 2023.

The public is invited to join the conversation about the environmental scoping phase of the State Route 239 Project during the public comment period.


The State Route 239 Project is offering an environmental scoping virtual open house. The purpose of environmental scoping is to identify the environmental topics that the project team should study to assess the potential environmental impacts of a construction project. Public input on this project will be critical for ensuring the SR 239 project team’s studies are comprehensive and thorough. Within the website you will be able to review informational materials about this phase of the work.

Please use the online comment form provided to send your thoughts and questions to the project team.

Virtual Environmental Scoping Meeting

Live presentation and Q&A session scheduled for January 20, 2022 at 5:30 p.m.

Recorded scoping presentation will be posted on the page on January 21, 2022.

On January 20, 2022, please visit the website for a link to the interactive virtual scoping meeting that will start at 5:30 p.m. Visitors will be permitted to join the meeting 15 minutes before the start time. The team will make a presentation about this project and a panel of experts will be available to answer your questions about State Route 239.

For additional information about this project, please contact Stephanie Hu – Director, Projects at



the attachments to this post:



Route 239 Goals


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