Evaluation of Force Density Levels of Light Rail Vehicles

Abstract

The vibration forces generated by train wheels rolling on steel rails are characterized as the force density level (FDL). FDLs are a key component in predicting vibration levels from future train projects and generally are assumed to be independent of the measurement position and the soil properties. FDLs are dependent on several factors, which include track type, vehicle suspension systems, train speeds, and condition of wheels and rail surfaces. Presented are results of train vibration measurements at three sites in Seattle, Washington, along Sound Transit's Central Link, and a comparison of the results with previous FDL results from Central Link's start-up phase. The effects of speed, train length, and track type on FDLs were measured. A test train was employed for the measurements at three sites. The tests at the three sites also included supplemental measurements with revenue service trains. The study showed that the vibration of the current Sound Transit fleet was lower than the previous measurements apparently because the wheels were in better condition than for the earlier tests. Rail roughness was also measured at all the test sites, and their effects on FDL were explored.