The Rio Vista Bridge (officially the Helen Madere Memorial Bridge) is a continuous truss span with a vertical-lift bridge in the middle which carries California State Route 12 across the Sacramento River at Rio Vista, California. The present bridge was completed in 1960 and is one of several moveable bridges spanning rivers in the Sacramento–San Joaquin River Delta. It is named after Helen Madere, who served as vice-mayor of Rio Vista. the bridge carries approximately 21,000 cars per day.
1919 bascule bridge
The original bridge spanning the Sacramento River was built in 1918 and opened in January 1919 at a cost of . From west to east, the 1919 bridge consisted of a concrete tied arch, the Strauss double-leaf bascule, three concrete tied arches and timber A-frame trestle spans.
1960 tower bridge
The 1919 bridge was replaced during seventeen years of piecewise construction. The finished 1943–1960 bridge consists of thirteen steel Warren truss spans (with one of those being the vertical-lift chorded Warren truss main span) carried on twelve piers. Total bridge length is , including of concrete slab approach spans on the west end of the bridge. Upon completion, the Rio Vista bridge won an American Institute of Steel Construction class IV (movable bridges) prize bridge award in 1960.
The main lift span weighs , with an equal amount in counterweights, so the lift mechanism operates using two electric motors, one in each tower. In the event of electrical failure, backup electrical power is provided by a diesel generator set. The main lift span can be raised to its full height in less than 90 seconds, although the total operating cycle can disrupt road traffic for 8–25 minutes. Clearance under the raised lift is to the highest anticipated water level, and the navigation channel is wide between the timber fenders protecting the tower piers. With the lift down, vertical clearance is only .
Construction 1943–1960
Less than thirty years after being completed, the eastern timber trestles of the 1919 bridge were in poor condition, and construction of replacement steel trusses began in 1943. Construction of the eastern steel truss section, consisting of seven truss spans, was completed in 1945 at a cost of , and traffic was diverted from the timber trestles onto the steel trusses with a crossover. The US Corps of Engineers authorized replacement of the remaining portion of the bridge on 2 February 1950, with contracts awarded for to Lord and Bishop for the substructure and to Judson Pacific Murphy for the superstructure, with an additional contract to Pacific Murphy for the concrete slab approach spans.
The substructure was constructed from 4 April 1957 through 30 October 1958, and consists of the concrete piers and pilings. The first part of the superstructure erected was the east tower, which began on 4 December 1958. The superstructure was assembled in prefabricated segments at Pacific Murphy's Richmond yard and barged upstream to the construction site, where they were raised into place by a capacity barge crane. The sheaves at the top of each tower were lifted in place during high tides in order to reach the necessary height. The 1960 superstructure replacing the 1919 bascule bridge includes the four truss spans west of the main lift span and one truss span east of the main lift.
The construction of the bridge overlapped the planning process for the Sacramento Deep Water Ship Channel. When plans for the Deep Water Channel were complete, the eastern truss section of the new bridge were already complete, and the Channel rerouted ship traffic from its then-current course near the western bank (through the 1919 bascule) to a point east. A new crossover from the 1919 bascule bridge to the 1945 steel truss spans was built to avoid interference with substructure construction, and after the new lift portion was built, another crossover was built to reroute road traffic from the 1919 bascule to the 1960 bridge. Once the new bridge was complete, removal of the old structure was completed by July 1960.