Author Topic: Sloping or overhanging barriers in Rail Noise Calculations  (Read 1169 times)

roger

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Sloping or overhanging barriers in Rail Noise Calculations
« on: December 03, 2018, 12:32:19 PM »
CRN and TNPM don’t provide for sloping or overhanging barriers.

NoiseMap did implement an overhanging capability for use in Hong Kong, where the overhanging barriers were also absorbent.

We are not aware of much in the way of research on this matter (other than measurements we took in Hong Kong), although admittedly we have not searched for recent work.  If users are aware of any guidance, then we will be glad to consider it.

For these reasons, the implementation in NoiseMap is very simple:  we assume that an overhanging barrier behaves as a simple barrier with the diffracting edge at the lip of the overhang.  We have assumed absorptive properties because we assume that there is no reverberant field within the enclosure space.  This is because the behaviour of sound within the space between the train and the semi-enclosure is not accurately defined. It will depend on many factors like separation distances.

Is the overhanging barrier tool is the best one to model the sloping barrier situation?
We think that if the diffracting edge is above the top of the train envelope, this would be the best way to do it. If the barrier slopes down toward the train, then reflections off the barrier will be directed downwards, so the assumption of absorbency would be reasonable.

If the sloping barrier is still at a distance from the nearside track, you could model it as a vertical barrier closer to the track and then you can choose whether or not to use absorbency.

This is an area that would benefit from further research.