Effect of Vehicle Speed on Sound Frequency Spectra

During analysis conducted on data collected by the University of Central Florida for the Florida Department of Transportation (FDOT), which was doing research to develop reference energy mean emission levels for high-speed traffic, other interesting data trends became apparent. One such trend was the relationship of vehicle speed and sound emission spectra. The data base contained real-time one-third octave band data and vehicle characteristics (e.g., speed) and permitted a detailed review of sound emission spectra with respect to vehicle speed. The purpose of this research was to attempt to develop a mathematical relationship between increasing vehicle speed and sound emission spectra. Based on the results of this research several important conclusions were drawn: (a) a trend in the change in sound frequency spectra with respect to vehicle speed may exist for all vehicle types defined in STAMINA 2.0; (b) the change in dominant frequency followed no apparent trend with respect to vehicle speed; (c) the data base used for this research was too small for accurate mathematical modeling of the change in sound frequency versus vehicle speed; and (d) the sound attenuation provided by noise barriers may be underestimated using the current method of estimating barrier attenuation based on an effective frequency of 500 Hz regardless of vehicle speed.