State Route 239 Project (old)

The 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. This new state route will ultimately improve the transportation network for an area that had few viable north-south roadway connections between East Contra Costa and the Central Valley.

This project is being led by the Contra Costa Transportation Authority (CCTA) in partnership with Contra Costa County and Caltrans.

The State Route 239 project is particularly important now, to provide relief from increasing commute traffic through the town of Byron, enhance mobility in East Contra Costa, and improve access to the Byron Airport.

Planned Milestones


IMPROVE north-south mobility between eastern Contra Costa County and western San Joaquin County
SUPPORT alternative modes of travel
SUPPORT connections to major emergency evacuation routes
ENHANCE goods movement between San Joaquin Valley and eastern Contra Costa County
REDUCE nonlocal traffic through the town of Byron
PROTECT natural resources and support adopted regional habitat conservation plans
IMPROVE access to Byron airport, which will support planned development

Project Areas

Brief History

State Route 239 has been a legislatively approved route since 1959. In 2009, Contra Costa County obtained federal funds to initiate a feasibility study and a project initiation document (PID). The PID document was completed in 2015 and the environmental phase has been initiated.

Why Now?

Supporting the growing communities of East 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 this 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 the outreach to be performed during future project development phases.For additional information about this project, please contact Stephanie Hu: