NoiseMap Forums
NoiseMap Software => Support => Topic started by: roger on October 15, 2013, 12:22:21 PM
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CRTN calculates L10 (18-hour) or L10 (1-hour) so if you want Lden, day, evening or night, you need to convert from L10 to Ld,e,n. There is a very strong correlation between the two units and TRL published a conversion method in 2003 in connection with the 'Noise Mapping England' project. However, it transpired that some implementations of CRTN sub-divide the road into many more segments than advised by CRTN, and this affected the resulting conversion to Ld,e,n. As a result, in 2005, TRL issued a slight revision to the conversion to remove the segmentation effect. NoiseMap is not affected by the segmentation problem so offers both methods. However, the 2005 method is now preferred. And the two methods may give marginally different results.
Both the 2003 and 2005 conversions offer 3 mthods - method 1 requires the full flow details for each of the 24 hour, method 2 requires flows for the 18 hours, plus d, e and n periods; method 3 requires just the 18-h flow, and is now the preferred method. However, if you have an unusual pattern of traffic (eg it is a managed motorway) you may want to use method 1. You don't actively stipulate the method: if you give 24 1-h flows, then method 1 will be used; if you give 18-h and d,e, and n flows, method 2 will be used and if you give just the 18-h flow, method 3 will be used.
If you wanted to use method 1 just to calculate Lnight, then you must still enter flows for each of the 24 hours, but you can use 'dummy' values for the hours you don't need - but the results for the dummy hours will then be dummy results.