Franklin Tunnel is a railway tunnel near Martinez, California. It carries the BNSF Railway Stockton Subdivision under the Briones Hills between Glen Frazer and the railroad's approach to the San Francisco Bay. It was built by the San Francisco and San Joaquin Valley Railroad just prior to the company's acquisition by the Atchison, Topeka and Santa Fe Railway. It opened for service in 1900 as the company's longest tunnel.