State Route 239 Project

A Virtual Public Scoping Meeting was held in December 2022. Visit the SR 239 Open House website for more information.

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 Transportation Authority (CCTA) in partnership with Contra Costa County and the California Department of Transportation (Caltrans) – District 4.

The proposed route is critical to the region as it will help 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. Our next major milestone will be the circulation of the Draft Environmental Document in 2025.


State Route Project timeline


IMPROVE north-south mobility between eastern Contra Costa County and western San Joaquin County

PROTECT natural resources and support adopted regional habitat conservation plans

IMPROVE access to Byron airport to support planned development

ENHANCE local and regional movement of goods

SUPPORT connections to emergency evacuation routes

SUPPORT alternative modes of travel 

REDUCE non-local traffic through the town of Byron

SUPPORT development and jobs within the area

Project Area

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.

Our recent project update


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 ongoing outreach during the project development phases.

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