Author(s): Byrne Stephen
Luas is Dublin’s modern light rail system. Similar to the majority of urban electrical tramways, the system is relatively quiet when compared to diesel locomotives with similar power output. However, electrical rail systems do produce airborne noise. The principle noise source is the interaction of the wheels with the rails; termed “rolling noise”. However, rail track type also influences noise emissions. A comprehensive review of acoustic compliance monitoring undertaken along the Luas network identified that rolling noise emissions were highest on straight sections of traditional slab track with speeds in excess of 50 km/ph. Measured levels were approximately 2-3dB higher than ballasted rail with similar speeds. Following a detailed consideration of available reduction systems the Railway Procurement Agency (now Transport Infrastructure Ireland), installed two track based noise reduction systems. Un-tuned rail dampers and bespoke absorbing rubber infill panels were installed on separate 100m stretches of the network. Pre- and post-installation attended monitoring was undertaken to determine external noise reductions achieved by each system. To take account of the varying nature of the noise levels from railways a number of indices were measured including LAeq,Tp, LAE and LAFMax to determine noise reductions achieved. One third octave band analysis was also undertaken. Tram pass-bys for the section of track installed with rail dampers decreased by up to 3.5dBA (LAE). For the section of track installed with the bespoke absorbing rubber infill panels tram pass-by levels decreased by up to 4dBA (LAE). Reductions were obtained at frequencies between 63Hz and 20kHz. The noise reduction systems trialled are suitable for use in tandem or in conjunction with other rail abatement measures including bogie shrouds and rail grinding. The findings of this research is being used when considering acoustic mitigation measures for future lines.
Name: Mr Stephen Byrne