2 Test Cases for a Straight Road

Corrected test cases for control of Nord2000-road

For a straight road 62 test cases have been developed to test nearly all aspects of the Nord2000 Road Traffic Model.

The horizontal distances in the terrain profile (x-coordinates) perpendicular to the road are measured from the centre line of the road. The road has two lanes, each 5 m wide, and the vehicles are driving in the middle of the nearest lane, and there is no traffic in the far lane.

The vehicles are category-1 vehicles (cars and vans) except in test cases 17 and 18 where vehicles are category-2 vehicles (dual-axle heavy vehicles), and category-3 vehicles (multi-axle heavy vehicles), respectively. In all cases a speed of 80 km/h has been used. The axle width is 1.5 m for category 1 and 2.5 m for categories 2 and 3. The road surface is assumed to be a DAC 12 (dense asphalt concrete with maximum aggregate size 12 mm).

The road is divided into 179 source points placed with constant angle seen from the receiver. The angle resolution is 1°, and consequently the source points cover horizontal immission angles between ±89°.

The results of the 62 cases are given in Excel spreadsheet “TestStraightRoad_20090216” with one worksheet for each test case. (yyyymmdd in the filename is the revision date; yyyymmdd = 20090216 indicates February 16, 2009). An example of a sheet is shown in Appendix A (Test Case No. 1). The main results are:

The sound exposure level L_AE and the corresponding spectrum L_E (unweighted) for the pass-by of a single vehicle
The 24-hour equivalent A-weighted sound pressure level L_Aeq,24h and the corresponding spectrum L_eq,24h (unweighted) for 10,000 vehicles per 24 hours
The A-weighted maximum level L_Amax
The propagation effect dL (for information, not required in the test process). The propagation effect is the difference between L_E and the “free-field” value of L_E (disregarding ground and screening effect as well as air absorption).

Besides the results, the sheet contains for each test case the model propagation parameters and the terrain profile given by the distance X from the road centre line perpendicular to the road, the height Z of the terrain, the ground flow resistivity, and the terrain roughness. In addition to the propagation parameters shown on the sheet the relative humidity of the air is 70%.

The 62 test cases for a straight road can be grouped with respect to the terrain shape as shown in Table 1.

Group 1 (flat terrain) contains test cases with variation in ground impedances, meteorological conditions and vehicle category. The remaining groups represent 11 different geometrical propagation cases, and for each group 4 calculations have been made: downwind, no wind, and upwind, all with a receiver height 1.5 m, and no wind with a receiver height of 4 m.

In group 12 (forest) additional parameters are needed to define the scattering zone which is not included in the information given in Appendix A. The scattering zone parameters are defined in Table 2.

Table 1: Test cases divided into 12 groups.

Group	Terrain description	Test cases nos.
1	Flat terrain	1-18
2	Flat mixed terrain (varying impedances)	21-24
3	Elevated road, roughness class N	31-34
4	Elevated road, roughness class M	41-44
5	Valley	51-54
6	Valley with a lake in the middle	61-64
7	Thin hard screen on flat ground	71-74
8	Thick hard screen on flat ground	81-84
9	Two screens on flat ground	91-94
10	Non-flat valley-shaped terrain	101-104
11	Non-flat hill-shaped terrain	111-114
12	Forest, flat terrain	121-124

Table 2: Definition of forest parameters in test cases 121-124.

Parameter	Value
x-start	10 m
x-end	80 m
nQ	0.075 m^-1
H	10 m
a,	0.1
k_p	1.25
a_trunc	0.15 m