High Street drawbridge
By kjfitz @ 2006-01-25 11:06:46
The High Street Bridge is a two lane double leaf bascule bridge, similar to the bridge at Park Street, which spans the Oakland Estuary for 296 feet. The Oakland Estuary is a navigable water way with access to the San Francisco Bay.
The original iron swing bridge was completed in 1894 by the Harrison Bridge Company for $24,747. This bridge, and the Park Street and Fruitvale Avenue bridges, were built by the U.S. Government in exchange for permission and rights-of-way to dredge the channel between San Antonio Creek and San Leandro Bay. In May 1901 a fire destroyed the swing span and part of the approaches, which were rebuilt the following year. The present bridge was designed by the County of Alameda Surveyors Office and constructed under the Federal WPA Program in 1939 at a cost of $750,000.
The High Street Bridge is a double leaf bascule bridge. Under normal operating conditions both leafs are used. Each leaf of the bridge can be operated independently. This gives the operator flexibility and helps keep the channel open for vessels in case one leaf is down for repairs.
The Bridge has two machinery rooms one for each leaf. Each leaf is powered by a 75 hp main motor and 5 hp backup motor. Each leaf is stopped by a service brake and emergency braking is supplied by a hydraulic brake system. Thousands of pounds of steel are lifted by 5 HP, then almost perfect counterbalancing. A huge counterweight supplies the balancing needed for the 100 plus foot long section of bridge. The Counterweight Pit is 40 feet below the roadway and when you stand on the pit floor it is only concrete that separates you from the water.
Each leaf of the bridge can open to a 76 degree position, this is considered a full opening. A normal opening is 45 degrees and can accommodate 95% of vessel traffic. With a full opening the bridge can accommodate almost any vessel. The main limiting factor would be vessel width and the depth of the channel. The bridge can operate safely under wind conditions reaching 30 mph. Over 30 mph wind conditions caution must be used when operating the bridge.