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The very rapid advance in the design of highway bridges is mainly due to the excellent work done by the various state highway commissions, and more recently the work dune by the U. S. Bureau of Public Roads. The author wishes to express his appreciation for the uniform courtesy of the various commissions and bureaus in furnishing plans and specifications. The author is under especial obligations to Mr. Clifford Older, bridge engineer of the Illinois Highway Commission; Mr. M. W. Torkelson, bridge engineer of the Wisconsin Highway Commission; Mr. J. H. Ames, and Mr. E. F. Kelly, bridge engineers of the Iowa Highway Commission; and Mr. C. V. Dewart, bridge engineer of the Michigan State Highway Department, for furnishing plans, specifications and data, without which this book could not have been written. The writer also wishes to thank the U. S. Bureau of Public Roads for furnishing the blue prints of their standard plans, which are reproduced in this book.

Credit is due Professor W. C. Huntington, University of Colorado, for assistance in preparing drawings and making calculations, to Professor R. S. Wallis, Missouri School of Mines, for assistance in preparing drawings; to H. C. Ford, for assistance in preparing drawings, and to C. L. Eckel, Assistant Professor of Civil Engineering in the University of Pennsylvania, for assistance in making calculations, preparing drawings and reading proof.

Milo S. KETCHUM UNIVERSITY OF PENNSYLVANIA,

PHILADELPHIA, PA. June 5, 1920.

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