Abstract: The current quality of our nations bridges is on a decline. There are roughly half a million highway bridges in the United States and out of the half a million more than 200,000 are deficient. With catastrophic failure of bridges causing the loss of life and property, the need for bridge inspection and maintenance is evident. When the Silver Bridge that crossed the Ohio River collapsed in December 1967, 46 people were killed. The failure to prevent the disaster was attributed to the poor inspection techniques used by the bridge inspectors. Current inspection techniques depend on humans being able to recognize structural imperfections without the aid of instrumentation. The Federal-Aid Highway Act of 1968 mandated both national bridge inspection standards and training for bridge inspectors. This act has encouraged the development of instruments that would allow inspectors to perform more complete inspections of bridges. To improve the quality of inspection and data, there is a great need for proven methods and instruments used to acquire data. The Laser Optical Displacement System (L.O.D.S.) developed at New Mexico State University by the Optical and Materials Science Lab is such a device. The L.O.D.S. has been tested and proven in both laboratory situations and in the field. This paper describes some of the methods that are now being used to measure deflections in bridges. Then, a description of the development and application of the L.O.D.S. unit is given. !8
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