# 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:

$LAeq=E+C_{o}+C_{r}-D_{a}-D_{l}-D_{b}-D_{m}$ $D_{l}=0.01\cdot d^{0.9}$ $D_{m}=max(0.0,3.5\cdot (1.0-e^{\frac {-0.04\cdot d}{h_{s}+0.75+h_{c}+0.75}}))$ where:

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

Default values are taken from InfoMil 

## Contents

### 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:

$C_{o}=1.4+{\frac {Q_{v}+Q_{t}+Q_{b}}{Q_{c}+Q_{v}+Q_{t}+Q_{b}}}$ ### Distance reduction

Distance reduction is computed as:

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

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

### Emission

Emission is computed as:

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

$E$ = the combined noise emission
$Ec$ = the calculated noise emission for cars
$Ev$ = the calculated noise emission for vans
$Et$ = the calculated noise emission for trucks
$Eb$ = 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:

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

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