traffic noise measurements have been made alongside 26 miles of the a66 within the lake district national park and in the towns of keswick and cockermouth. the measurements in the towns form the first part of a before and after survey, ultimately to assess the noise benefits to be derived from by-passes which are due to be completed in 1975. the measurements made along the rural sections have been used to derive and validate a noise prediction model appropriate to both the conditions found alongside the a66 and for rural areas generally. the prediction method is based on the trrl traffic noise computer model. validation studies indicate that the standard error of the differences between the observed and predicted results was 2.5 db(a). however, a large proportion of the standard error can be attributed to the effects produced on the measured results by varying meteorological conditions. given this constraint it is unlikely that the accuracy of the prediction can be improved, but it nevertheless can be recommended for planning and assessment purposes. the method has been used in this study to construct a 50 db(a) l10 contour for traffic on the existing a66 and for projected traffic conditions on a planned improved route of the a66. (a)

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