# Traffic noise formula (Traffic Noise Overlay)

The calculations for the Traffic Noise Overlay follow the standard rekenmethode 1 (SRM 1), as described on http://wetten.overheid.nl/BWBR0031722/2015-07-01#BijlageIII:

${\displaystyle LAeq=E+C_{o}+C_{r}-D_{a}-D_{l}-D_{b}-D_{m}}$

${\displaystyle D_{l}=0.01\cdot d^{0.9}}$

${\displaystyle D_{m}=max(0.0,3.5\cdot (1.0-e^{\frac {-0.04\cdot d}{h_{s}+0.75+h_{c}+0.75}}))}$

where:

${\displaystyle LAeq}$ = equivalent noise level (dB(A))
${\displaystyle E}$ = calculated emission
${\displaystyle C_{o}}$ = acceleration term on intersections (default = 0 dB(A))
${\displaystyle C_{r}}$ = reflection term. This term is not used, and by default 0 dB.
${\displaystyle D_{a}}$ = distance reduction
${\displaystyle D_{l}}$ = air reduction (default = XXX dB(A))
${\displaystyle D_{b}}$ = surface reduction. This term is not used, and by default 0 dB.
${\displaystyle D_{m}}$ = calculated meteorological reduction
${\displaystyle d}$ = distance from the receiver to the source.
${\displaystyle e}$ = Euler's number, approximated as 2.7182.
${\displaystyle h_{s}}$ = Building datum height (DTM) of the noise source
${\displaystyle h_{c}}$ = Building datum height (DTM) of the noise receiving cell.

Default values are taken from InfoMil [1]

### Acceleration term on intersections

Accelerating on intersections can cause more noise. This value is only calculated for roads of category INTERSECTION. It is calculated as followed:

${\displaystyle C_{o}=1.4+{\frac {Q_{v}+Q_{t}+Q_{b}}{Q_{c}+Q_{v}+Q_{t}+Q_{b}}}}$

### Distance reduction

Distance reduction is computed as:

${\displaystyle D_{a}=10\cdot log(r)}$

where:

${\displaystyle D_{a}}$ = distance reduction
${\displaystyle r}$ = shortest distance between the source and point of evaluation

### Emission

Emission is computed as:

${\displaystyle E=10\cdot log_{10}(10^{\frac {Ec}{10}}+10^{\frac {Ev}{10}}+10^{\frac {Et}{10}}+10^{\frac {Eb}{10}})}$

where:

${\displaystyle E}$ = the combined noise emission
${\displaystyle Ec}$ = the calculated noise emission for cars
${\displaystyle Ev}$ = the calculated noise emission for vans
${\displaystyle Et}$ = the calculated noise emission for trucks
${\displaystyle Eb}$ = the calculated noise emission for buses

The emission per type of traffic is computed similarly, with values specific to the type of traffic. It is calculated as followed for car traffic:

${\displaystyle Ec=E_{c,start}+E_{c,mult}\cdot log_{10}({\frac {V_{c}}{V0_{c}}})+10\cdot log_{10}({\frac {Q_{c}}{V_{c}}})+\sigma +\tau \cdot log_{10}({\frac {V_{c}}{V0_{c}}})}$

where:

${\displaystyle E_{c,start}}$ Emission start value. Configurable with model attribute Emission start (Traffic Noise Overlay). See also: InfoMil [2]
${\displaystyle E_{c,mult}}$ Emission factor. Configurable with model attribute Emission mult (Traffic Noise Overlay). See also: InfoMil [3]
${\displaystyle V_{c}}$ = The traffic type's speed, configured in roads with Function Value TRAFFIC_SPEED.
${\displaystyle V0_{c}}$ = The traffic type's reference speed, configured per traffic type using the model attribute V0.
${\displaystyle \sigma }$ = road surface correction value at reference traffic speed. Configurable in roads with Function Value TRAFFIC_NOISE_SIGMA
${\displaystyle \tau }$ = road surface correction factor per 10 km/hour deviation from reference traffic speed. Configurable in roads with Function Value TRAFFIC_NOISE_TAU

## Notes

• If the traffic amount is defined as a single value, that value is used for all defined hours. However, if the amount if an array of values, each of the 24 indexes of that array are assumed to correspond to the hour denoted by those indexes, and as such that specific value from the array is used.