Acoustic roughness outcomes from rail maintenance processes

Rail roughness is a key determinant of the rolling noise emissions of many railway systems, particularly those systems where wheel roughness is relatively low. Rail roughness can vary considerably. The noise emissions from trains operating on very smooth, quiet, worn in systems can be 25 dBA less than the noise from identical trains operating on the same trackform but with rough or corrugated rails. Rail roughness varies over time, with changes resulting from gradual wear during normal operations but also from maintenance interventions. Rail grinding, milling or acoustic polishing can cause immediate and sometimes dramatic changes in rail acoustic surface condition, and noticeable changes in noise character. This paper documents the acoustic roughness outcomes achieved by various rail maintenance processes, in comparison to acoustic roughness from worn in tracks. The data presented includes measurements of surface finish from conventional rail grinding, rail milling, and from newer specialist acoustic grinding technologies. The rail roughness results are used to demonstrate the differences in noise emissions following rail maintenance activities. The results confirm the importance of maintaining low rail roughness as a means of noise control at source.