The U.S. Department of Transprotation, Research and Special Programs Administration, Volpe National Transportation Systems Center, in support of the Federal Railroad Administration is conducting a research program with the goal of reducing the number of fatalities and injuries at higway-railroad grade crossings. As part of this program, the Volpe Center's Noise Measurement and Assessment Facility is conducting a study to determine the effectiveness of railroad horn systems. This document is the first publication supporting this study. It presents the results of acoustic measurements performed in Council Bluffs, Iowa, Jacksonville, Florida, Cambridge, Massachusetts, and Omaha, Nebraska, to determine the acoustic characteristics of several types of railroad horn systems. Data obtained includes frequency spectrum, directivity, drop-off rate, maximum A-weighted sound level, and sound exposure level.