PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Road Traffic Noise Prediction Model “ASJ RTN-Model 2018”
Proposed by The Acoustical Society of Japan– Part 1: Outline of the calculation model
Shinichi SAKAMOTO1; Yasuaki OKADA2; Akinori FUKUSHIMA3;
Toshio MATSUMOTO4; Terutoshi TAJIKA5
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Faculty of Science and Technology, Meijo Universityǡ ͵  Ǥ, Japan
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  Ǥǡ ABSTRACTThe Acoustical Society of Japan (ASJ) has published a new version of road traffic noise prediction
method “ASJ RTN-Model 2018” this April. The technical committee on road traffic noise in the AcousticalSociety of Japan had been working for structuring the road traffic noise prediction models in conformity withthe times for decades, and “ASJ RTN-Model 2018” is an up-grade version of the previous model, “ASJ
RTN-Model 2013”, published in 2014. In developing the new version, existing knowledge is widely taken
into account, in particular, specification of sound power levels of vehicles and calculation methods for soundpropagation are improved in wide range. This new model is introduced in five papers with the same main title
in this congress. In this paper, the framework of the model, the calculation principle, the general procedure ofprediction calculation, the outline of the revision, are described.
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1. INTRODUCTION
Road traffic noise is one of the most representative environmental issues worldwide. In Japan, theAcoustical Society of Japan organized the Technical Committee on Road Traffi c Noise and thecommittee has continued researches on the road traffic noise issues of Japan for over 40 years. As aresult of the research activity, a series of the prediction model of road traffic noise named ASJ Model(up to the Model 1998) and ASJ RTN-Model (Model 2003 and later) has been published (1-7). In
Japan, the models have played important roles on noise assessment in the future environment (basedon the Environmental impact Assessment Law) and noise estimation in regular environmental
monitoring (based on the Noise Regulation Law). As a result, they have considerably contributed torealization of the quiet society in Japan. After release of ASJ RTN-Model 2013 published in 2014,
the research committee has been working to improve the prediction model on the basis of the latest
data and knowledge for five years, and the latest version named “ASJ RTN-Model 2018” waspublished this April. This new model is introduced in five papers with the same main title in thiscongress. In this paper (Part 1), the calculation principle, the general procedure of the prediction
calculation and the outline of the revision are described. The calculation models of sound power
levels of road vehicles and calculation methods of sound propagation are introduced in Part 2 (8) andPart 3 (9), respectively. In addition, accuracy verification of the calculation method of noise in1sakamo@iis.u-tokyo.ac.jp
okada@meijo-u.ac.jp
3fuku-new@wonder.ocn.ne.jp
4matsumoto@kobayasi-riken.or.jp
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build-up areas is introduced in Part 4 (10). Finally, the prediction accuracy of this model is shown inPart 5 (11).

2. SCOPE
The conditions applicable to ASJ RTN-Model 2018 are as follows.
(1) Types of road: General roads (flat, bank, cut and viaduct) and special road sections (interchanges,
junctions, signalized intersections, road tunnels, depressed/semi-underground roads, flat roads withoverhead viaducts and double-deck viaducts).
(2) Traffic volume: No limitation.
(3) Running speed of vehicles: 40 to 140 km/h for sections of steady traffic flow on expressways
and general roads, 0 to 60 km/h for sections of non-steady traffic flow section on general roads, 0 to
80 km/h for acceleration/deceleration sections on expressways such as interchanges, 0 to 60 km/h foracceleration/deceleration sections on general roads such as in the vicinity of signalized intersections.
(4) Prediction range: Up to a horizontal distance of 200 m from the road under consideration and up
to a height of 12 m above the ground. The validity of the model has been examined for thisprediction range; however, the model is applicable without any limitation o n the calculation range.
(5) Meteorological conditions: conditions of no wind and no strong temperature profile are assumed
as the standard condition.

3. GENERAL PROCEDURE AND BASIC FORMULAE
3.1 Principle and basic formulae
In ASJ RTN-Model, the equivalent continuous A-weighted sound pressure level, L Aeq,T, at a
prediction point is calculated. As the first step to calculate L Aeq,T, the “unit pattern”, a time history ofA-weighted sound pressure level at a prediction point for a single vehicle that is considered to be apoint source passing along the road under consideration is obtained, and the sound pressure exposurelevel, L AE, for the single vehicle is calculated. By taking account of the traffic conditions (traffic
volume, vehicle type composition, etc.) in the above results, the time-averaged value of the noise at
a prediction point in terms of energy is calculated. The concrete procedure is as follows.
First, the objective road (lane) is divided into several sections as shown in Fig. 1. Here, runningspeed v i [m/s] and sound power level LWA,i of the running vehicle at i-th divided section should be
regarded as constant. One of the sections is selected and a representative point (source point) is set atthe center point of the section, and the A-weighted sound power level, LWA,i , is set. Next, soundpressure level, L A,i, at the prediction point is calculated according to calculation method of soundpropagation. Sound pressure exposure level for the i-th section,

LAE ,Ti ,i , during the interval Ti in

which the vehicle exists in the i-th section is calculated as follows (see Fig. 2).

LAE ,Ti ,i

T
LA,i  10 lg i
T0(1)

where T 0 = 1 s (the reference time). The above calculation is performed for every section. Then, thesingle event sound exposure level L AE [dB] at the prediction point when a vehicle travels along theentire road (lane) is calculated as
LAE ,Ti ,i

LAE 10lg ¦10 10(2)iSound power level is dependent on the vehicle type. Therefore, the single event sound exposurelevel L AE is calculated for each vehicle type, and the equivalent continuous A-weighted soundpressure level L Aeq,T is calculated by taking into consideration of the traffic volume for the vehicle
type.

¦ N 10T, j

LAeq,T

10 lg i

LAE ,i10(3)T

where T [s] is the total time interval, L AE,j [dB] is a single event sound exposure level for vehicle
type j calculated by Eq. (2), NT,j is the traffic volume (number of vehicles) of the vehicle type jduring the time interval T.

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Road

Time

Prediction point
Figure 1 – Sound propagation from a soundsource to a prediction point.

Calculation procedure(A) Setting of road structure and roadsidecondition(B) Setting of prediction point

Figure 2 – Unit patternCalculation conditions
x Types of road under considerationx Geometry of roadside terrain, acoustical obstacles
x Positions of source s, prediction points and acoustical obstacles
x Type of ground surfaces(C) Setting of calculation lane position(s)and discrete source positions(D) Setting of sound power level of source

x Type of pavement (dense asphalt concrete, porous asphalt
pavement, Gap-graded asphalt mixture (KOUKINOU II) )x Running mode of vehicles (steady, unsteady, acceleration,
deceleration, idling)x Running speed (each vehicle type)(E) Calculation of unit pattern (propagation

x Corrections (road gradient, directivity, etc.)
x Correction for acoustical obstacles (position, height, width,
installation range, type of noise reducing device on the top)x Grand effect (type of ground)x Sound reflection from boundary (shape of boundary,position, absorption coefficient of the surface)x Atmospheric absorption (temperature, relative humidity)x Attenuation by buildings (height of buildings, perspective
angle of road, etc.)

calculation) [by lane, by vehicle type](F) Calculation on energy integral of unit
pattern with respect to time[by lane, by vehicle type ]if necessary(G)

Energy summation

Calculation of LAeq [by lane, by vehicle type]x Traffic volume by lane, by vehicle typeCalculation of LAeq for structure borne noiseof viaductx Type of viaduct, traffic volume,
running speed of heavy vehicles

Estimation of variation due to effect of windx Mean wind speed

LAeq for all lanes and all vehicle types

Figure 3 㸫 Calculation procedure for predicting road traffic noise
3.2 General calculation procedure
A flow showing the general procedure for calculating road traffic noise based on this model isshown in Fig. 3. The outline of the calculation procedure is as follows.
(A) Setting road structures, roadside conditions and prediction point
The first step of the procedure includes setting the road structure, the positions of the source, theprediction point, and the acoustical obstacles, the ground surface conditions along the propagation

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path and so on.
(B) Setting positions of lanes
The calculation position for each lane is located at the center of the lane. For simplicity of thecalculation, it is possible to combine two or more lanes into a single hypothetical lane. For instance,a hypothetical lane can be located along the centerline between two lanes of traffic traveling in
opposite directions.
(C) Setting discrete source positions
Discrete source positions are generally located within a range of r20l (l: shortest distance fromthe calculation lane to the prediction point) from the point of intersection of lines representing thelane and the perpendicular from the prediction point on the lane. They are located with an interval ofl or less. On the other hand, in the cases where vehicle running speed varies by accelerationdeceleration as seen in special road sections or where the propagation property rapidly changes withthe arrangement of the sound source, the prediction point and other acoustical factors, it may benecessary to shorten the intervals of the discrete sources in order to capture the maximum level ofthe unit pattern correctly, and in order to obtain accurate value of single event sound exposure levelof the unit pattern, the point sources should be set in the range where the sound pressure level goes
down to -10 dB or less than the maximum level.
(D) Setting the power level of the source
LWA is set considering the type of pavement of the road surface, the running condition of thevehicle (steady flow, non-steady flow, acceleration, deceleration and idling while at rest), runningspeed and corrections (power-level change due to the type of pavement, road gradient, directivity
and other factors).
(E) Calculation of the unit pattern
The unit pattern L A;i at the prediction point is calculated when a single vehicle runs alone along
the objective road. The unit pattern is calculated separately by lane and by vehicle type.
(F) Calculation of the energy integration of the unit pattern and L Aeq
Single event sound exposure level L AE for respective vehicle type by Eq. (2). Taking into
consideration of traffic volume NT during the evaluation time T [s], equivalent continuous
A-weighted sound pressure level L Aeq,T is obtained by Eq. (3).
(G) Calculation of total noise level
When the road has multiple lanes exist, L Aeq,T for all of the lanes is calculated by the energy
summation of the obtained results for respective driving lanes. In the case of noise prediction arounda viaduct road, the structure-borne noise of the viaduct is taken into consideration in addition tovehicle noise. If a viaduct has a structure separated by a gap between lanes, the noise is calculated byconsidering that each set of lanes exists independently. Sound attenuation caused by the variation ofsound due to the effect of wind can also be calculated when required.
Finally, L Aeq,T for the entire road is obtained.

4. OUTLINE OF REVISIONSThe present model is developed based on the previous version, ASJ RTN-Model 2013 (7), and thefollowing points are revised to the previous version.
(1)Sound source characteristicsx
The classification of road vehicle from an acoustical viewpoint was reviewed and it waschanged from the conventional four-category classification (large-sized vehicles, medium-sized
vehicles, small-sized vehicles and passenger cars) to the three-category classification(large-sized vehicles, medium-sized vehicles and light vehicles).
x
Based on the latest knowledge regarding the sound power levels of recent vehicles, values of thecoefficients for the calculation formulae of the A-weighted sound power levels of vehicles were
updated.
x
In the previous versions of ASJ RTN-Model, the calculation formulae of the A-weighted soundpower levels of vehicles was basically given for dense asphalt concrete road, and correction
terms were applied for porous power levels of vehicles were given for respective types of theroad pavement.
x
In the types of road pavement, gap-graded asphalt mixture (referred to as “KOUKINOU II”),
which is often used in cold snowy regions in Japan due to its high durability, was newly
included.
x
Based on the latest data on recent road vehicles, sound power spectra of vehicle noise were3693

updated.
The latest knowledge on the A-weighted sound power levels of hybrid vehicles (HVs) andelectric vehicles (EVs) are given.
(2) Propagation calculationx
The corrections due to sound attenuation by diffraction and reflection were reviewed and a partof calculation formulae and values of coefficients were updated.
x
For correction for diffraction, sound diffraction over knife wedge (assuming a barrier) and thatover right-angled wedge (assuming an embankment or a building) were discriminated andformulae for respective fundamental correction terms were given.
x
According to update of sound power spectra of vehicles and addition of gap-graded asphalt
mixture to road pavement type, values of the coefficients for calculation formulae on correction
terms on diffraction were updated.
x
According to the introduction of fundamental term on right-angled wedge diffraction, thecalculation method of thick barrier was changed.
x
In addition, applying the calculation method of the thick barrier, calculation method foroverhung barrier was also changed. Noise shielding effects of overhung barriers were modeled
as summation of the noise shielding effect of a hypothetical thick barrier with the same
diffraction point as the objective overhung barrier and the specific shielding effect to the type ofthe overhung barrier, and the calculation method based on such a modeling was given.
x
For ground effect, calculation method for ground effect over porous asphalt pavement was
newly added.
x
For scattered reflection method included in calculation method of sound reflection, method ofsetting of the calculation condition was described.
x
On the basis of numerical investigation of meteorological effect on sound propagation of roadtraffic noise, upper limit of attenuation effect due to diffraction and ground effect wasdetermined.
x
Calculation method of frequency-dependent propagation was updated to generalizedenergy-base method.
(3) Special road sectionsx
Calculation method of noise around road tunnel was changed to the method taking into
consideration of directivity characteristics of sound radiation from tunnel mouth.
x
For noise around flat/overhead roads and double-deck viaduct, calculation method of scatteredreflection was simplified.
(4) Noise behind a single building and in build-up areasx
For road traffic noise in build-up areas, calculation method based on a point source model givenin the previous model was simplified from an engineering viewpoint and the content was
updated.
x
The detailed calculation method based on a point source model was described in Appendix inorder to meet the necessity in which detailed unit patterns should be calculated.
x

5. CONCLUSIONSAs mentioned above, ASJ RTN-Model 2018 is basically an energy-base calculation method based on
LAeq and can be applied to almost all types of roads, in principle. This prediction model will be effectively
used for the environmental impact assessment and regular environmental monitoring in Japan. At the sametime, this model can be applied to noise mapping of existing environment. However, there still exist various
kinds of problems that should be solved in the future. For this aim, the Research Committee on Road
Traffic Noise in the Acoustical Society of Japan will continue the research work.

REFERENCES
1. K. Yamamoto, Road traffic noise prediction model “ASJ RTN-Model 2008”: Report of the ResearchCommittee on Road Traffic Noise, Acoust. Sci. & Tech., 2010; 31, 2-55.
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(J), 1975; 31, 507-517 (in Japanese).
3. H. Tachibana, Energy-base prediction method of road traffic noise from general types of roads (Reportfrom Research Committee of Road Traffic Noise in Acoustical Society of Japan), J. Acoust. Soc. Jpn.
(J), 1994; 50, 227-252 (in Japanese).

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4. Research Committee of Road Traffic Noise in Acoustical Society of Japan, ASJ Prediction Model 1998
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