Nordic Prediction Method 1996
Two types of evaluation parameters may be calculated using the Nordic Prediction Method (NPM) for road noise (TemaNord 1996:525NPM525-1996):
- the A-weighted equivalent continuous sound pressure level LA,eq and
- the A-weighted maximum sound pressure levels LAFmax X% or LAFmax N-th (for details see below FÖR216-2015 RET1442-2016).
Further, the number of events NATd/e/n above a threshold level can be calculated.
Since the equivalent continuous level LA,eq is calculated per day (24 h) no specific day- or nighttime values exist in NPM. It is stated, however, that any other period could be assessed as well using LA,eq provided the traffic data refers to this period. In contrary, separate procedures are used to calculate maximum levels.
Note
In CadnaA, the emission level LAeq*,10m as shown on the dialog Road refers to the A-weighted equivalent continuous sound pressure level LA,eq as emission parameter, corrected for road surface and gradient. When calculating the A-weighted maximum sound pressure level LAFmax the emission parameter shown is still the level LAeq*,10m.
Dialog Road (for Nordic Prediction Method)
Emission Level LA,eq
The A-weighted equivalent continuous sound pressure level LA,eq at 10 m distance from the road’s axis of an infinite straight road with free sound propagation calculates from the sound exposure levels for each vehicle category (light and heavy traffic):
- level for light traffic:
\(L_{Aeq,10 m}(\text{light})=L_{AE,10m}(\text{light})+10 \lg \frac{N(\text {light})}{T} \text{dB(A)}\)
- level for heavy vehicles (m > 3500 kg):
\(L_{Aeq,10 m}(\text{heavy})=L_{AE,10m}(\text{heavy})+10 \lg \frac{N(\text{heavy})}{T} \text{dB(A)}\)
and for both contributions:
\(L_{Aeq,10m}(\text{mixed})=L_{Aeq,10m}(\text{light})++L_{Aeq,10m}(\text{heavy})\)
where ++ represents the energetic sum.
The sound exposure levels for each category result from:
- light traffic:
v>=40 km/h: \(L_{AE,10m}=73.5+25 \lg \frac{v}{50} \text{dB(A)}\)
30<=v<40 km/h: \(L_{AE,10m}=71.1 \text{dB(A)}\)
- heavy vehicles (m>3500 kg):
50 km/h <= v <= 90 km/h: \(L_{AE,10m}=80.5+30 \lg \frac{v}{50} \text{dB(A)}\)
30 <= v <= 50 km/h: \(L_{AE,10m}=80.5 \text{dB(A)}\)
and \(L_{AE,10m}(v<=30\text{km/h})=L_{AE,10m}(v=30\text{km/h})\)
Emission Level LAFmax
The calculation of the A-weighted maximum sound pressure level LAFmax refers to the percentage X% of the vehicles (light & heavy) exceeding this level (see Nordic Prediction Method (1996)).
Note
Make sure to have selected the evaluation parameter/s LmaxD/E/N (see Evaluation Parameters Tab).
LAFmax X%, 10m
The arithmetic mean level \(\overline{L_{AFmaxX\%,10m}}\) due to an exceedance by X% of the vehicles calculates from equations 2.29 to 2.33 in Part 2 of NPM525-1996 using a numerical approximation of the normal distribution function (to obtain y(X%) ):
- for light traffic:
v>=30 km/h: \(\overline{L_{AFmaxX\%,10m}} = 69+30 \lg \frac{v}{50}+y(X\%)*\text{Sigma}_{Light}\) dB(A)
with \(\text{Sigma}_{Light}=5.5*e^{-0.7\frac{v}{50}}\) dB
and \(L_{AFmax,10m}(v<=30\text{km/h})=L_{AFmax,10m}(v=30\text{km/h})\)
- for heavy vehicles (m > 3500 kg):
v>50 km/h: \(\overline{L_{AFmaxX\%,10m}} = 75+30 \lg \frac{v}{50}+y(X\%)*\text{Sigma}_{Heavy}\) dB(A)
with \(\text{Sigma}_{Heavy}=10*e^{-0.9\frac{v}{50}}\) dB
v<=50 km/h: \(\overline{L_{AFmaxX\%,10m}} = 75+y(X\%)*\text{Sigma}_{Heavy}\) dB(A)
with \(\text{Sigma}_{Heavy}=4.1\) dB
Example
The level LAFmax exceeded by 5% of the vehicles calculates with a factor of y(5%)=1.64.
Protocol with LAFmax
When calculating the maximum level the CadnaA protocol still shows the results for the Leq calculation and thus does not apply.
LAFmax, N-th vehicle
The calculation of the A-weighted maximum sound pressure level LAFmax of the N-th loudest vehicle (light & heavy) during the night is based on the normal distribution function as used for the calculation of LAFmax X% (for input of number N see Nordic Prediction Method (1996)).
Note
Make sure to have selected the evaluation parameter LmaxN (see Evaluation Parameters Tab).
Example
The calculation procedure - referring to the Swedish software „Buller Väg“ by Trivector AB - is as follows (here for an 8 h night and the 5-th loudest vehicle):
- calculate the numbers Ncars and Ntrucks during the entire night:
\(N_{\text{cars}}=N_{\text{night}}*n_{\text{night}}*\frac{100-p\%_{\text{night}}}{100}\)
\(N_{\text{trucks}}=N_{\text{night}}*n_{\text{night}}*\frac{p\%_{\text{night}}}{100}\)
- if Ntrucks>0 calculate the value X% for trucks to calculate the level LAFmax X% using the normal distribution function for trucks:
\(X\%_{\text{trucks}}=\frac{5}{N_{\text{trucks}}}*100\)
if \(X\%_{\text{trucks}}>50/%\) then \(X\%_{\text{trucks}}=50\%\)
- if Ntrucks=0 calculate the value X% for cars to calculate the level LAFmax X% using the normal distribution function for cars:
\(X\%_{\text{cars}}=\frac{5}{N_{\text{cars}}}*100\)
if \(X\%_{\text{cars}}>50/%\) then \(X\%_{\text{cars}}=50\%\)
with
- Nnight: number of vehicles per hour during night (cars & trucks)
- nnight: number hours per night (e.g. 8 h)
- p%night: percentage of trucks during the night (HGVnight)
Note
If either conditions are met (X%>50% then X%=50%, i.e. with 10 or less cars/trucks during night) the level LAFmax,N-th vehicle becomes independent from the number N entered.
In order to convert data given for MDTD and percentage into the input data Nnight and p%night required in CadnaA the following transformation scheme can be used:
| Parameter | Explanation / Equation | |
| Input data | MDTD p%24h p%N pL%N n |
Mean Daily Traffic Density, vehicles/24h % heavy traffic, 24h % heavy traffic, night % light traffic, night hours per night |
| Intermediate data | heavy vehicles/24 h | A = p%24h * MDTD |
| light vehicles/24 h | B = MDTD *(1-p%24h/100) | |
| heavy vehicles (night) | C = A * p%N | |
| light vehicles (night) | D = B * pL%N | |
| CadnaA input data | vehicles per hour (Night), MN | (C+D) / n |
| percentage heavy vehicles (Night), PN | C/(C+D) * 100 |
Example
Path: Examples\Configuration\Nordic-Road
The referenced xlsx-file shows this transformation scheme for an example situation while the respective CadnaA file is included as well.
NATd/NATn
Swedish law FÖR216-2015 prescribes to check, besides the maximum level itself,
- whether a maximum level of 70 dB(A) is exceeded more than 5 times for each hour during daytime (16 hours, so 16*5=80 exceedances during the entire daytime), and
- whether a maximum level of 70 dB(A) is exceeded more than 5 times within the entire night-time (8 hours), and
- whether a maximum level of 80 dB(A) is not exceeded at all times.
This evaluation can be achieved by using the evaluation parameters NATd (for Day) and NATn (for Night), see Evaluation Parameters Tab, and by specifying the length of the Day (16 h) and Night (8 h) periods, see Reference Time Tab. Further, a threshold level has to be specified on the „Road“ tab (see Nordic Prediction Method (1996)).
As long as traffic count data Day/Night is used (MDTD, N/p%, or diurnal pattern) the number of events above the entered threshold level NATd/NATn is calculated from the hourly traffic counts.
Note
Since each individual road contributes to NATs, do not split a distinct road into sections (i.e., into a line of different road objects). This would result in doubling the NATs, at least in the joint‘s vicinity.
Example
Path: Examples\ Sources\ Road\ Nordic 96
 |
 |
| NATd above 70 dB(A) during day (16 h) | NATn above 70 dB(A) during night (8 h) |
| NOTE - Consider that the values displayed inside the building evaluation symbol refer to the first two evaluation parameters (here 1:Ld, 2:LmaxD, while 3:NATd, 4:NATn). | |
MDTD
The „Mean Daily Traffic Density“ (MDTD, vehicles/24h) does not exist in NPM as an input parameter for traffic data. Nevertheless, this feature is provided by CadnaA applying the road types of the Austrian road noise standards RVS 3.02 RVS-1997 and RVS 4.02 RVS-2006. The respective data is given in the tables below.
from RVS 4.02, tables 1 and 2:
| Attribute Value STRGATTNR |
Road Type | Day (6-19 hrs) | Evening(19-22 hrs) | Night (22-6 hrs) | |||
| N (veh/h) | p (%) | N (veh/h) | p (%) | N (veh/h) | p (%) | ||
| 2 | national road | 0.060 * MDTD | 10 | 0.036 * MDTD | 15 | 0.014* MDTD | 25 |
| 3 | local road | 0.064 * MDTD | 10 | 0.029 * MDTD | 10 | 0.010 * MDTD | 10 |
| 4 | main road | 0.062 * MDTD | 10 | 0.035 * MDTD | 5 | 0.011 * MDTD | 10 |
| 5 | service road | 0.062 * MDTD | 5 | 0.041 * MDTD | 2 | 0.009 * MDTD | 2 |
from RVS 3.02, tables 1 and 2:
| Attribute Value STRGATTNR |
Road Type | Day (6-22 hrs) | Night (22-6 hrs) | ||
| N (veh/h) | p (%) | N (veh/h) | p (%) | ||
| 0 | local 3.02 | 0.065 * MDTD | 10 | 0.007 * MDTD | 5 |
| 1 | national 3.02 | 0.065 * MDTD | 15 | 0.013 * MDTD | 25 |
with
-
N: number of vehicles per hour
-
p: percentage of heavy vehicles
Note
Speed correction in RVS refers, as it does in NPM, to 50 km/h.
For the percentage of light/heavy trucks it holds for both (see RVS 3.02, tab. 3 and RVS 4.02, tab. 3):
| Road Type | Percentage of Heavy Vehicles | |
| light trucks (%) | heavy trucks (%) | |
| national (4.02 & 3.02) | 25 | 75 |
| local (4.02 & 3.02) | 90 | 10 |
| main road | 60 | 40 |
| service road | 95 | 5 |
Source Geometry
The height entered in the dialog Geometry is the height of the road surface. The source height is 0.5 m above the road’s center line or above the center lines of the outer lanes.
Speed Limit (km/h)
According to NPM the real speed is used in the prediction, not the indicated speed limit. When the real speed is, however, not available the „posted speed“ should be used instead.
Road Surface
In CadnaA, the emission level is corrected with different road surfaces, even when NPM originally states this correction to be a part of the propagation model.
The following table lists the types of road surfaces and their respective level corrections.
road surface corrections according to NPM, Annex A, Table A1:
| Attribute Value STRONR |
Road Surface | Correction in dB(A) for a certain % of heavy vehicles | |||||||
| 0-60 km/h | 61-80 km/h | 80-130 km/h | |||||||
| 0-5 | 6-19 | 20-100 | 0-5 | 6-19 | 20-100 | 0-5 | 6-100 | ||
| 1 | 1a Asph.concr. (12-16mm) | ref | ref | ref | ref | ref | ref | ref | ref |
| 2 | 1b Asph.concr. (12-16mm) | 0 | 0 | -1 | -2 | -1 | -1 | -2 | -2 |
| 3 | 2a Asph.concr. (8-10mm) | 0 | 0 | 0 | -1 | 0 | 0 | -1 | -1 |
| 4 | 2b Asph.concr. (8-10mm) | -1 | -1 | -1 | -2 | -1 | -1 | -2 | -2 |
| 5 | 3a Mastic asph. (12-16mm) | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 |
| 6 | 3b Mastic asph. (12-16mm) | 0 | 0 | 0 | 1 | 0 | 0 | 1 | 0 |
| 7 | 4a Mastic asph. (8-10mm) | -1 | -1 | 0 | -1 | -1 | -1 | -1 | -1 |
| 8 | 4b Mastic asph. (8-10mm) | -2 | -1 | 0 | -2 | -2 | -1 | -2 | -2 |
| 9 | 5 Chipped asphalt (BCS) | 1 | 0 | 0 | 2 | 1 | 0 | 2 | 1 |
| 10 | 6a Chip seal Y1 (16-20mm) | 1 | 0 | 0 | 2 | 1 | 0 | 2 | 1 |
| 11 | 6b Chip seal Y1 (16-20mm) | 2 | 1 | 0 | 3 | 1 | 0 | 2 | 1 |
| 12 | 7a Chip seal Y1 (10-12mm) | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 13 | 7b Chip seal Y1 (10-12mm) | 0 | 0 | 0 | 0 | 0 | -1 | 0 | 0 |
| 14 | 8a Chip seal Y1 (6-9mm) | 0 | 0 | 0 | -1 | 0 | 0 | -1 | 0 |
| 15 | 8b Chip seal Y1 (6-9mm) | -1 | 0 | 0 | -1 | -1 | -1 | -1 | -1 |
| 16 | 9a Chip seal Y2 (16-20mm) | 0 | 0 | 0 | 1 | 0 | -1 | 0 | 0 |
| 17 | 9b Chip seal Y2 (16-20mm) | 1 | 0 | 0 | 1 | 0 | -2 | 0 | 0 |
| 18 | 10a Chip seal Y2 (10-12mm) | 0 | 0 | 0 | 0 | 0 | -1 | 0 | -1 |
| 19 | 10b Chip seal Y2 (10-12mm) | 0 | 0 | 0 | 0 | -1 | -2 | 0 | -1 |
| 20 | 11a Porous asph. (14-16mm) | 0 | 0 | 0 | -1 | -1 | -1 | -1 | -1 |
| 21 | 11b Porous asph. (14-16mm) | --1 | -1 | 0 | -1 | -1 | -1 | -1 | -2 |
| 22 | 11c Porous asph. (14-16mm) | -2 | -2 | -2 | -2 | -2 | -3 | -2 | -3 |
| 23 | 12a Porous asph. (8-12mm) | 0 | 0 | 0 | -1 | -1 | -1 | -2 | -2 |
| 24 | 12b Porous asph. (8-12mm) | -1 | -1 | -1 | -2 | -2 | -2 | -3 | -3 |
| 25 | 12c Porous asph. (8-12mm) | -3 | -3 | -3 | -4 | -4 | -5 | -5 | -5 |
| 26 | 13 Cem.concr. (20-80mm) | 2 | 1 | 1 | 2 | 2 | 2 | 2 | 2 |
| 27 | 14 Cem.concr. (12-18mm) | 1 | 1 | 1 | 2 | 2 | 2 | 2 | 2 |
| 28 | 15 Cem.concr.,ground | -1 | -1 | -1 | -2 | -2 | -2 | -1 | -1 |
| 29 | 16 Paving Stones | 3 | 3 | 2 | 5 | 4 | 3 | 5 | 4 |
| 30 | 17 Cement block pavement | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
Gradient (%)
In CadnaA, a varying road gradient corrects the emission level already, even when NPM originally states this correction to be a part of the propagation model.
The correction for the road gradient ΔLst (in dB) results from:
\(\Delta L_{st}=\frac{2G}{100}+\frac{3G}{100} \lg (1+p)\)
with
-
G: gradient in %o (10%o =1%)
-
p: proportion of heavy vehicles (in %)
In CadnaA, the road gradient is specified in % instead.
Note
When calculating the A-weighted maximum sound pressure level LAFmax no gradient correction is applied (even not when option „Road Gradient: auto“ is selected).
Correction for Multiple Reflections
NPM provides an overall correction for multiple reflections in side streets where the noise impact results from a main street (section 2.6.9 of part 2 of NPM525-1996). As this correction alters the normal distance correction it is part of the propagation model and, thus, not part of the emission model. However, the correction ΔLms can be entered manually on the dialog Road, with activating the configuration option „Calc exactly one Reflection Order“ (see Nordic Prediction Method (1996)). When applying the correction for multiple reflections the maximum number of reflections calculated using image sources should be restricted to the first order.
When the option „Distance“ is selected, the correction ΔLms is calculated from the distance for each receiver position.