Only the centre line of the road is to be given directly into Novapoint Noise. The road's gradient, heights in noise sources, placement and heights of the road edges are collected from the terrain model. To get these values correct, there has to be done a preparation in the terrain model before registering the road's centre line in Novapoint Noise (see Preparing of roads in the terrain model). If the map basis is not good or the road edges are not satisfactory defined, this may lead to an incorrect gradient. In the dialog box Define gradient we have the opportunity to change the calculated gradient data (see Gradient).

If there is no centre line in the terrain model, and we can't get the centre line from other relations, we have to design a centre line. This may be done in AutoCAD. The centre line must as close as possible to the middle point between the road edges, and it should hit a 1-1,5 m wide imaginary corridor in the middle of the road. For calculation points lying 10 m from the road , a 1 m error in localization of the centre line could cause roughly 0,5 - 1 dBA wrong calculation result. When the distance between calculation point and the centre line is large, larger inaccuracies in the placement of the centre line may be tolerated.

The centre line has to be a polyline. It should be continuous on the entire road section. The following AutoCAD functions may be used to design a centre line:

• Polyline 2D: Draws a continuous polyline
• Offset: Makes a parallel to polyline/line (may make parallel to edge line)
• Copy: Copies e.g. polyline/line (may copy edge line)
• Pedit: Editing of polyline, e.g. unite polylines, move point on polyline, delete point on polyline, split polyline, add to polyline, make spline from polyline etc. (see AutoCAD user's manual for guidance).

Using Novapoint functionality for horizontal alignment design the line may be drawn and you may make a 10 table from it etc. With that it may be entered into the Road model.

Four-lane roads should be entered as two roads. The two lanes to the right are assembled to one road, and the two lanes to the left are assembled to one road. A centre line will have to be defined for each of the two roads. The centre line will have to be located between the lanes in each of the two roads. Three-lane roads are entered as one road, while roads with five, six or seven lanes are entered as two roads. Roads with eight or more lanes are entered as four roads.

The calculations in Novapoint Noise are automatically terminated, no matter how long the entered road section is. (see Calculation).