Third Street Bridge (34C0024) is a double-leaf, bascule structure with concrete counterweights and concrete abutments. The two bascule arms allow boats to pass on Islais Creek (a shipping channel); they consist of riveted steel girders supporting an open, steel-grate roadway. The sidewalks, which are also open, steel grates, are supported by brackets attached to the outer girders. The bridge span is approximately 105 feet. At the four corners of the bridge, the gears for the bascule arms are contained in metal housings of quarter-circle shape. These housings are detailed in a streamlined, Art Moderne style. There is also a raised, center median. The control tower located at the northeast corner of the bridge consists of a concrete tower topped by a glass control room. The tower is oblong in shape, with rounded ends. A projecting balcony with metal pipe railings surrounds the control room. The control room has a flat roof with large, plate glass windows canted slightly outward.