Stage 2:  Preliminary screening study

Preliminary screening prediction studies provide a means of gauging the potential criticality of the prediction outcomes, and identifying critical source elements, transmission paths, and assessment locations. These studies are relatively brief, and valuable for defining the scope of any future work. They proceed as follows:

1. Clearly define any thresholds at which differing assessment outcomes are triggered. This might take the form of a threshold defined in a planning condition or contract.
   
   
2. Identify the assessment (receiving) locations.
   
   
3. Gather preliminary sound source type and position data.
   
   
4. Apply a very simple propagation assumption such as hemispherical spreading.
   
   
5. Produce very rough estimates of the expected noise levels at the identified assessment locations for comparison with the thresholds or limit values.

In some instances, gathering information about the sound sources may be problematic. In these cases, it may be possible to consider the separation between the source and assessment locations, and use this information to work back to the magnitude of sound emission levels that would be needed to trigger differing assessment outcomes.

Screening studies then lead to one of the following outcomes:

• No further studies are required, since the output information is already sufficient to enable a decision to be made, and further detailed studies would not provide any benefit to the study.
  
  
• The available information suggests that further detailed studies can be averted by a revised screening study.
  
  
• A refined sound propagation model must be designed. The findings may provide guidance as to the areas on which to focus.
  
  
• Predictions with a risk level commensurate with project requirements cannot be made and a different approach must be sought.