I Street Bridge, Historic railway and road bridge in Sacramento, United States

The I Street Bridge is a steel truss double-deck swing bridge over the Sacramento River between Sacramento and West Sacramento. Its upper deck carries the street that gives it its name, while the lower deck holds two Union Pacific tracks used by BNSF and Amtrak. The riveted brown steel lattice rises above the lower deck, and a white sign near the right end reads "I STREET BRIDGE".

The Southern Pacific Railroad and the governments of Sacramento and Yolo counties agreed on 14 February 1910 to build a new steel bridge; work began on 8 June 1910 and the bridge opened on 29 April 1912, at a cost of $1 million. It was the fourth railroad bridge at this crossing, following structures dating back to 1870. Its 3,000-ton swing span was then the heaviest rotating steel truss in the world. It was listed in the National Register of Historic Places in 1982.

The bridge demonstrates early twentieth-century engineering methods and reflects the rapid infrastructure development that occurred during California's growth period. It served as a vital transportation hub connecting people and goods between Sacramento and surrounding areas.

The upper roadway has a vertical clearance of 14 feet 8 inches (4.47 m) and carries a walkway on each side of the road. The deck is too narrow for buses and has no bicycle facilities, with very narrow sidewalks. Trains use the lower level, close to Sacramento Valley Station.

The structure features a rotating central mechanism that can pivot on its axis to allow river vessels to pass through. This innovative design choice kept the waterway open for commercial shipping while maintaining road and rail connections.