the original bridge, known as the san francisco bay toll bridge, opened on 1929-03-02 after approximately a year of construction. it was a privately owned venture and was then the longest bridge in the world. the original bridge was mostly a two-lane causeway trestle with five truss spans in the center incorporating a vertical lift over the main shipping channel. clearance when the lift was down to allow road traffic over the bridge was , and clearance when the lift was up to allow marine traffic to pass the bridge was .