SR 239 is an unconstructed route that would connect Interstate 205 and Interstate 580 west of Tracy with SR 4 at Byron along an alignment close to County Route J-4 (Byron Road).

SR 239 was added to the Freeway and Expressway system in 1959. The Contra Costa County Transportation Authority (CCTA) evaluated the possibility of the route linking I-205 or I-580 with SR near Brentwood in 2005. The TriLink study in 2012 considered three alternatives for the route, including using Byron Road and two new alignments. Caltrans District 10 analysis however found that the connecting location was not ideal, and that it would not provide sufficient traffic relief between the Tracy and Brentwood areas.1

CCTA submitted for a full build-out of SR 239 in accordance with the Metropolitan Transportation Commission (MTC) and TriLink for the 2017 regional transportation plan (RTP). It was rejected and the CCTA instead submitted the Vasco Road Byron Highway Connector Road and the SR 239 Feasibility Studies and Project Development, two smaller projects.1



Sources:

  1. Transportation Concept Report - Unconstructed State Route 239. Caltrans District 10, March 2017.

    Page Updated 06-26-2018.