Noise and Vibration Report - Transnet

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ENVIRO-ACOUSTIC RESEARCHSCOPING NOISE REPORT – TRANSNET: SWAZI RAIL LINK – DAVEL YARD TO NERSTON RSA ROUTE4.2.1.1 Train movementRail traffic is considered as a line source of noise with a continuous area of impact bothsides of and parallel to the railway line. Railway related noise is general acousticallycharacterised by high noise levels of relatively short duration. The wayside noise radiatedinto a community is the function of a number of different factors, namely:• interaction of wheels and rails;• the vehicle or locomotive propulsion system;• type of locomotive and wagons;• braking technology employed on the wagons and locomotives;• railway alignment, in particular the design radius of curves and turns;• auxiliary equipment;• noise radiated from vibrating structures;• train speed;• train length;• aerodynamics (for high speed operations);• locomotive warning devise or horn noise.Train speed is a major influence parameter for noise emission. The noise due to tractionand auxiliary systems (diesel units, electrically driven powertrains, cooling equipment,compressors), if present, tends to be predominant at low speeds, up to around 60 km/h.Wheel-rail rolling noise is dominant up to speeds around 200-300 km/h, after whichaerodynamic noise takes over as dominant factor. The transition speeds from tractionnoise to rolling noise and from rolling noise to aerodynamics noise depend entirely on therelative strength of these sources. The rolling noise, for example, depends strongly onthe surface condition (roughness) of wheels and rails, whereas aerodynamic noisedepends on the streamlining of the vehicle. The relationship with speed is illustrated inFigure 4-1.P a g e | 25
ENVIRO-ACOUSTIC RESEARCHSCOPING NOISE REPORT – TRANSNET: SWAZI RAIL LINK – DAVEL YARD TO NERSTON RSA ROUTEFigure 4-1: Railway exterior sound sources and typical dependence on trainspeed4.2.1.2 Rail loop operations 2Rail loops, also known as passing loops, are implemented at sections of the rail wheretrains travelling in opposite directions on a single track can pass each other. A fewoptions may be envisaged for the rail loop namely:• Main and loop or similar alternatives: The main line has a straight track, while theloop line has low speed turnouts at either end;• Dead-end siding: It is possible to allow trains to pass each other with a simple railsiding. Potentially there could be a significant source of a highly impulsive soundas the wagons slam into each other during coupling if applicable; and• Potential diesel fuelling stations may be implemented at a rail loops enablingservicing of locomotives to their required destination.Noise levels due to brake squeal as trains approach the rail loop could range between the90 to more than 105 dBA (peak). It can be audible for more than 2,000 meters. Thecharacter of this noise can be considered tonal and could also increase annoyance levelswith receptors.2 http://en.wikipedia.org/wiki/Passing_loopP a g e | 26
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Noise and Vibration Report - Transnet

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