Page:Popular Science Monthly Volume 91.djvu/581

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Safeguarding Our Bridges

��The cushion gate and the yielding barrier are two effective remedies

RECENT accidents in Boston, Chicago and Vancouver have at last aroused ■ the public to the realization that changing conditions have made obsolete devices used at the present time to protect bridge approaches and railroad crossings. A cushion barrier gate devised by the Chicago bureau of engineering seems to solved the problem of the improperly protected bridge approach and the yield- ing chain bar- rier for railroad crossings prom- ises to do much to lessen the number of accidents.

The cushion barrier gate, which has been installed at the Lake Street bridge, in Chi- cago, consists essentially of a forty -two-foot boom of Doug- las fir, sixteen inches in diam- eter, suspended

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���from the top of the bridge by two heavy twelve-inch pipes. The boom, which weighs a ton, serves as a buffer to stop a street car or automobile running at high speed without wrecking it or causing serious injury to the occupants. When a car bumps into the boom, the boom rolls for two feet, then slides for eight feet, and then for the next five feet slides and rises two feet, so that the car not only has to

��Automobile run- ning into the yielding chain barrier, which consists of a steel truss strung between uprights

��overcome the inertia of a heavy weight but acts against gravity on a total weight of over five tons. Danger of dropping the boom on a street car is eliminated by an ingenious device. Each time a street car enters the bridge, it auto- matically turns a cog wheel one notch. The boom, which is in position against the top of the framework, cannot be dropped by the bridge tender until the car pushes forward another cog wheel when it passes off the bridge at the other end.

The lighting system, which is also unique, has proved highly effective. The engineers have utilized the well-known principle, little used for bridge signals, that a light which goes on and off at short intervals catches the eye quicker than any other. The red lights first come on at the "Stop" sign at the left. Then in quick succession the lights in the gate at the left, in the gate at the right, and the "Stop" sign at the right

��The cushion barrier gate which re- cently stopped a street car running at ten miles an hour without damag- ing the car. See diagram at left

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