Tri Delta Transit, formally the Eastern Contra Costa Transit Authority, is a joint powers agency of the governments of Pittsburg, Antioch, Oakley, Brentwood, and Contra Costa County that provides bus service for the eastern area of Contra Costa County, California, United States.

[1] Tri Delta Transit local buses connect to the BART rapid transit system at Antioch, Pittsburg Center, Pittsburg/Bay Point and Concord.

[4] Tri Delta Transit operates in eastern Contra Costa County and has stops in Antioch, Oakley, Brentwood, Bay Point, Pittsburg, Martinez, and Concord.

Major transfer points for the majority of Tri Delta Transit's routes include: Tri Delta Transit operates seventeen bus routes.

On weekdays, all of them are operated throughout the cities of Concord, Bay Point, Pittsburg, Antioch, Oakley, Brentwood, and Martinez.