Comparison of Two Metrics for Assessing Human Response to Vibration

Abstract

The United States Federal Transit Administration has recently recognized the vibration criteria contained in ISO 2631 Part 2 as the criteria to be used in assessing environmental impacts for new rail projects in the USA. This is specified in the latest version (May 2006) of the FTA publication Noise and Vibration Impact Assessment for Rail Transit. The FTA preferred prediction model for vibration is the empirical based model of Nelson and Saurenman, in use for over 20 years. The force density level (FDL) component of their model is obtained from field measurements of train induced ground vibration. Analysis of the data to obtain an FDL can be achieved by measuring either the L _eq of the train passby signature or by recording one-second RMS averages (the metric specified by ISO 2631) over the duration of the passby and determining the “maximum value” for a passby. Both approaches have been used by different practitioners to evaluate new transit lines and assess human response to groundborne vibration and noise. Obviously the two methods can produce different results, but to what degree. Ground vibration data for two different transit train systems (one light rail and one heavy rail) were analyzed both ways and the results compared. The implications for the prediction of groundborne noise and vibration are presented and discussed.