You have used automatic segmentation to generate the road segments and you have set the tolerance to a low value - maybe 0.1 metre - so the segments are very short on curved sections of the road.
But you have also left the cut-off angle at COA=1.0, that is, 1 degree. The cut-off angle causes NoiseMap to ignore segments of road that subtend a small angle at the receiver. This helps to speed up calculation by ignoring segments where the angle of view correction is a large (negative) value and so the amount of noise from the segment would be small. However, if all your segments are short, this results in a large proportion of the road being ignored. In such a case, you should reduce the cut-off angle, perhaps to the lowest value of 0.1 degree, so that only the very shortest segments would be ignored.
You can check the effect of cut-off angle by using Calculate>Show Source Contribution. This will show you the segments that giving no contribution at a given receiver point.
Digitising with a low tolerance gives segments that follow the curvature of the road beautifully but CRTN was originally intended to be used with a small number of long segments, and there is little evidence that a low tolerance (following the road alignment precisely) produces a significantly better result. Remember that NoiseMap automatically sub-divides segments according to the way that multiple barriers affect the screening, and in cases with many buildings or noise barriers, this can result in thousands of further sub-divisions, which are not affected by the cut-off angle.
