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 2: Calculation model of sound emission of road vehicles
Yasuaki OKADA1; Akinori FUKUSHIMA 2; Katsuya YAMAUCHI 3; Shinichi SAKAMOTO 4
1

Faculty of Science and Technology, Meijo University, Japan
2
3

4

NEWS Environmental Design Inc., Japan

Faculty of Design, Kyushu University, Japan

Institute of Industrial Science, The University of Tokyo, Japan

ABSTRACTThe Acoustical Society of Japan (ASJ) has published a new revised version of road traffic noise prediction
model “ASJ RTN-Model 2018”, in which the calculation formula for the A-weighted sound power level ofeach type of road vehicles is specified. The sound power level is given basically as a function of the runningspeed in consideration of practicality and convenience. The Research Committee in ASJ has been
accumulating new data about noise emission of vehicles running on expressways and general roads over thelast decade. As results, the sound power level of light vehicles, which include passenger cars, hybrid vehicles
and small-sized vehicles, for the dense asphalt pavement was changed to a lower value than those in theprevious model. In addition, the calculation formula for sound emission on the porous asphalt pavement wasrevised, and that on the road paved with the gap-graded asphalt mixture (GGAM, referred to as“KOUKINOU II”) was introduced into the model. In this paper, the revised model of the sound power leveland power spectrum for road vehicles based on the newly acquired data are described.
Keywords: Sound Power Level, Power Spectrum, Hybrid Vehicles

1. INTRODUCTION
The calculation formulas for the A-weighted sound power level L WA of road vehicles have beendeveloped based on a large amount of pass-by noise measurements performed at roadsides of
expressways and general roads (1, 2). The sound power level depends not only on the vehicle type but
also on the running condition, pavement type and so on. The basic calculation formula for L WA is given
as a function of the running speed, and the influences of other factors are considered in the correction
terms. The most measurement data used for determining the formulas have been acquired in 1991–
1998 for the dense asphalt pavement, and in 1996–2008 for the porous asphalt pavement (3-5),
respectively. On the other hand, in order to improve those models more accurately, the ResearchCommittee has been accumulating new data about noise emission of road vehicles after the previous
model was published. In this paper, the revised model of sound power level and power spectrum forroad vehicles using the newly acquired data are described. In addition, the differences between L WA on
the dense asphalt pavement and on the road paved with the gap-graded asphalt mixture (GGAM)
introduced into the new model are presented.

2. CLASSIFICATION OF ROAD VEHICLESIn ASJ RTN-Model 2018, road vehicles are basically classified into two or three categories, as
shown in Table 1. The three-category classification (light vehicles, medium- and large-sized vehicles)
places importance on noise radiation characteristics, while the two-category classification (light and1okada@meijo-u.ac.jp
fuku-new@wonder.ocn.ne.jp
3yamauchi@design.kyushu-u.ac.jp
4sakamo@iis.u-tokyo.ac.jp
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heavy vehicles) takes practicality into account. In the prediction of road traffic noise, not only thesound power level of each road vehicle but also the percentage of each type of vehicle comprising thetraffic volume is an important factor. Thus, the percentage of heavy vehicles (medium- and large-sized
vehicles) in the two-category classification is widely used in the environmental impact assessment ofroads. Additionally, the noise generated from motorcycles can be also considered separately.
Table 1 – Vehicle categories defined in ASJ RTN-Model 2018.
Two-category

Three-category

Passenger cars used exclusively for carrying passengers with capacity of 10 or
fewer*Small-sized vehicles with engine displacement exceeding 0.050 liter and withoverall length of 4.7m or lessLight vehicles

Medium-sized
vehiclesHeavyvehiclesLarge-sized
vehiclesMotorcycle

Characteristics

Vehicles with overall length exceeding 4.7m excluding large-sized vehicles(most vehicles in this category have 2 axles)
Medium-sized buses with capacity from 11 to 29 passengers
Vehicles with gross vehicle weight of over 8 t or maximum authorized payloadof over 5 t (most vehicles in this category have 3 or more axles).
Large-sized buses with capacity of 30 or more passengers
Large-sized special motor vehicles
Motorcycles and mopeds

Note: * In the previous model (ASJ RTM-Model 2013), light vehicles were classified into two types: passenger cars andsmall-sized vehicles. However, these vehicle types are specified in the same category, because the ratio of number of theregistered small-sized vehicles to passenger cars decrease to about 14% in recent years.

3. SOUND POWER LEVEL OF ROAD VEHICLESThe sound power level of road vehicles generally varies not only with the road vehicle type, butalso with the running condition of vehicle and pavement type. In this model, the sound power level isset separately for pavement types and sections taking into account vehicle running conditions, which
are defined as follows.
Types of pavement (see Fig.1):(a) Dense asphalt pavement: road surface with a dense asphalt concrete pavement(b) Porous asphalt pavement: porous asphalt with a maximum chipping size of 13 mm and a designed void
content of 20%(c) Gap-graded asphalt mixture (GGAM): porous asphalt, which is referred as to “KOUKINOU II”, formedin layers with the top layer having a maximum chipping size of 13 mm and the bottom layer of stone
mastic asphalt (SMA).
Porous asphalt pavement

Gap-graded asphalt mixture

I13 mmtop

40 – 50 mm

I13 mmtop

SMA

Figure 1 – Schematic of porous asphalt pavement and gap-graded asphalt mixture (GGAM).
Types of section taking into account vehicle running conditions:(a) Steady traffic flow section: This is a section of expressway or general road sufficiently distant fromsignalized intersections, where vehicles can be driven in top-gear position or equivalent. The vehicle3697

running speed V is in the range from 40 to 140 km/h (see Fig.2).
(b) Non-steady traffic flow section: This is a general road including signalized intersections, where vehicles
frequently accelerate and decelerate. The speed V is in the range from 10 to 60 km/h (see Fig.2).
(c) Acceleration section: The running condition in this section is defined as a transitional state from thestopping condition at an expressway tollgate to the steady running condition in the main lane. The speed
V is in the range from 1 to 80 km/h. Acceleration at speeds exceeding 80 km/h is treated as the steadyrunning condition. Also, a constant power level is applied at speeds of less than 1 km/h (see Fig.5).
(d) Deceleration section: The running condition in this section is defined as the transitional state from thesteady running condition in the main lane to the stopping condition at the tollgate. The speed V is in therange from 10 to 140 km/h. A constant power level is applied at speeds of less than 10 km/h (see Fig.5).
3.1 Sound Power level of Road Vehicles on Dense Asphalt
In this model, the sound power level for each type of road vehicles is given basically as afunction of the running speed, similarly to that in the previous model for practicality andconvenience. The A-weighted sound power level L WA of a road vehicle running on the dense asphalt
pavement is given by(1)‫ܮ‬ௐ୅ = ܽ + ܾ lg ܸ + ‫ܥ‬,
‫ = ܥ‬ο‫ܮ‬୥୰ୟୢ + ο‫ܮ‬ୢ୧୰ + ο‫ܮ‬ୣ୲ୡ,(2)
where V is the vehicle running speed [km/h], a and b are regression coefficients, and C is thecorrection term for the change in the sound power level due to the road gradient 'L grad [dB], soundradiation directivity 'L dir [dB] and other factors 'L etc [dB]. The calculation methods for these
corrections were assumed to be the same as the previous model.

10dB

Non-steady traffic flow section
LWA= a + 10 lgV + C

Steady traffic flow section
LWA= a +30 lgV + C

0

20

40

60

80

100

120

140

Figure 2 – Illustration of LWA in steady and non-steady traffic flow sections (dense asphalt pavement).
Figure 2 shows an illustration of L WA on the dense asphalt pavement in the steady and non-steadytraffic flow sections. The coefficients a, b for each vehicle type in the both sections are given in Table
2. For the determination of the coefficient b which represents the running speed dependence of thegenerated noise, the pass-by noise measurements have been performed on test tracks and several
general roads using each type of vehicle. As results of those studies (4, 5), it was revealed that thevalue of coefficient b can be given by 30 for steady traffic flow section, and 10 for non-steady traffic
flow section, respectively.
The coefficient a depending on vehicle types was determined using the pass-by measurement data
conducted at actual roads. The newly acquired data for L WA of each vehicle type was 4,529 for lightvehicles, 688 for medium-, and 606 for large-sized vehicles. From the measurement results, L WA forlight vehicles on the dense asphalt pavement was changed to 0.9 dB lower than that in the previous
model (0.9=46.7–45.8, Table 1). The principal reason of this change in L WA is that the number of thelow-emission vehicle such as hybrid and electric vehicles (HVs/EVs) and mini-sized vehicles (also3698referred to as K-cars) are increasing year by year. The discussion on L WA of those road vehicles is
described in subsequent section. On the other hand, for heavy vehicles including medium- andlarge-sized vehicles, the collected L WA were the same as that adopted in the previous model. The othercalculation formulas for LWA in acceleration and deceleration sections on the dense asphalt pavement
were assumed to be the same as the previous model, and please refer to the model (1).
Table 2 – Coefficients a and b for LWA on urban roads (dense asphalt pavement).
Steady traffic flow section(40 km/h  V  140 km/h)

ClassificationaLight vehicles

45.8

Heavy vehicles

53.2

Medium-sized vehicles

51.4

Large-sized vehicles

54.4

Motorcycles

46.9

Non-steady traffic flow section(10 km/h  V  60 km/h)

b

a

b

82.3

30

88.8
87.1

30

90.0

30

85.2

10
10
10

3.1.1 Low Emission Vehicles
The number of the registered mini-sized vehicles and HVs/EVs in Japan are shown in Fig.3. At
end of March 2017, the number of the registered mini-sized vehicles and HVs/EVs contained in the
category of passenger cars are about 2,200 million and 70 million, respectively. The percentage ofthese vehicle types are about 35% and 10% of overall passenger cars during the last five years. In
particular, the market share of HVs/EVs is expected to grow in the future.
As mentioned the previous section, L WA for light vehicles obtained from the newly acquired data
were revealed to be lower than that adopted in the previous model. Therefore, the measurement dataof passenger cars were divided into conventional gasoline engine vehicles (GEVs), HVs/EVs, andmini-sized vehicles, and LWA for those types of road vehicles were compared with each other.
80[million]

Passenger cars

60

Mini-sized vehicles

40(2013–17/ 34–36%)
20

8

HVs / EVs

6(2013–17/ 6–12%)

4
2
0

1997

2007

Examples of mini-sized vehicles (also referred to as
K-cars, displacement: 0.66 lit., overall length: 3.4m)

2017

Figure 3 – Number of registered mini-sized vehicles and HVs/EVs in the category of passenger cars.
Table 3 – Coefficient a for vehicle types in the category of light vehicles.
ClassificationaMeas. number

45.3

4,221

Conventional GEVs

45.8

2,527

HVs

45.2

451

Mini-sized vehicles

44.3

1,243

Small-sized vehicles

48.1

308

Passenger cars

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120
110
100
90
80
70

30

40

50

60

70

80

90

30

40

50

60

70

80

90

30

40

50

60

70

80

90

120
110
100
90
80
70

Figure 4 – Speed dependence of LWA for conventional GEVs, HVs and mini-sized vehicles(Passenger cars, n: number of data, r: correlation coefficient, s: standard error).
Table 3 and Figure 4 show the coefficients a in the formulas for L WA of each vehicle type containedin the category of light vehicles. The number of the acquired data were 2,527 for GEVs, 451 for HVs(including two EVs), and 1,243 for mini-sized vehicles. The L WA for HVs and mini-sized vehicles were
0.6 dB and 1.5 dB lower than that for conventional GEVs, respectively. The reasons for the decrease in
L WA of light vehicles could include the increase in the number of these low-emission vehicles.
Furthermore, the noise reduction effect of the low-emission vehicles can be expected in the vicinityof signalized intersections or expressway tollgates, where are dominated by the power-unit noise ofvehicles (6-8). The accumulating measurement data of L WA for HVs/EVs and examination of the noise
reduction effect by the low-emission vehicles are necessary for assessing road traffic noise in the
future environment.
3.2 Sound Power level of Road Vehicles on Porous Asphalt
Regarding the porous asphalt pavement and GGAM, the sound power level L WA for each type ofroad vehicles is given as functions of the running speed and the number of years since the pavement
was constructed, as follows:(3)‫ܮ‬ௐ୅ = ܽ + ܾ lg ܸ + ܿ lg(1 + ‫ )ݕ‬+ ‫ܥ‬‫ = ܥ‬ο‫ܮ‬୥୰ୟୢ + ο‫ܮ‬ୢ୧୰ + ο‫୲ܮ‬୰ୟ୤ + ο‫ܮ‬ୣ୲ୡ
(4)
where a, b and c are regression coefficients, and y indicates the number of years since the pavement
was constructed. Among the correction terms C, 'L traf is a term taking into account the changes innoise reduction effect depending not only on the elapsed years y, but also on the daily traffic volume.
However, the relationships between the traffic volume and noise reduction effect of the porous
pavement have not yet been analyzed quantitatively. Therefore, the correction value 'L traf is assumed
to be 0 dB. Figure 5 shows an illustration of L WA on the porous asphalt pavement in the accelerationand deceleration sections near an expressway tollgate. The examples of coefficients a, b and c forporous asphalt pavement are given in Table 4, and those for GGAM are presented in Table 5,
respectively.
To determine the coefficient a, b and c in the steady traffic flow section, the pass-by noise
measurements have been conducted on 17 expressways paving with porous asphalt, and 7 expressways
paving with GGAM (9). Also, the annual changes in L WA was examined using the measurement data
performed up to 11 years for the porous asphalt pavement, and up to 7 years for GGAM. The traffic
volume of the target road was almost 15,000 or less vehicles per day for measuring noise generated
from a single running vehicle. In ASJ RTN-Model 2018, from these examination results, the3700

coefficients b which represents the running speed dependence of LWA is fixed at 25 for the porous
asphalt pavement, and at 30 for GGAM, respectively. In the case of motorcycles, the noise reduction
value by these low-noise road surfaces is 0 dB. Besides, the formulas for L WA in the acceleration
section was assumed to be the same as the previous model (Table 4).

Acceleration section
LWA= a + 10 lgV + c lg (1+y ) + C

10dB

Steady/ Deceleration section
LWA= a + 25 lgV + c lg (1+y ) + C
LWA: Constant

0 1

20

40

60

80

100

120

140

Figure 5 – Illustration of LWA near an expressway tollgate (porous asphalt pavement).
Table 4 – Coefficients a, b and c for LWA near an expressway tollgate (porous asphalt pavement).
Steady/ Deceleration section(60 km/h  V / 1NPKV )ClassificationaLight vehicles

50.6

Heavy vehicles

57.7

Medium-sized vehicles

56.5

Large-sized vehicles*

58.7

Motorcycles

49.6

b
25
25
30

Acceleration section(1  V  60 km/h)(60  V  80 km/h)

c

a

1.5

79.1

0.6

87.4

0.7

85.7

0.5

88.6

–

87.7

b
10
10
10

c

a

6.4

88.0

3.6

96.3

3.6

94.6

3.6

97.5

–

87.7

b
5
5
10

c
6.4
3.6
3.6
3.6
–

*Except for large-sized buses (a = 56.1, b = 25, c = 0.5) in the case of steady/ deceleration section

Table 5 – Coefficients a, b and c for LWA near an expressway tollgate (GGAM).
Classification

Steady traffic flow section (6 V  140 km/h)
aLight vehicles

45.2

Heavy vehicles

50.3

Medium-sized vehicles

49.5

Large-sized vehicles*

50.9

Motorcycles

49.6

b
30
30
30

c
0.1
0.4
0.5
0.4
–

*Except for large-sized buses (a = 47.9, b = 30, c = 0.4)

Figure 6 shows a comparison of the calculated A-weighted sound pressure levels L A between
different pavement types under the steady running conditions. In this calculation, the coefficients for
L WA of light and heavy vehicles (two-category classification) in steady/ deceleration section are used,
and the elapsed years y and the percentage of heavy vehicles comprising the traffic volume isassumed to be zero and 20%. At a running speed of 80 km/h, it can be seen that the noise reduction
compared with conventional dense asphalt pavement is 4.9 dB for porous asphalt pavement, and 1.8
dB for GGAM, respectively.

3701

5dB

Dense asphalt

GGAM
Porous asphalt

40

60

80

100

Figure 6 – Comparison of calculated LA of road traffic noise between different pavement types(steady/ decreasing running conditions).
0

-10

-20

-30
A-weighted levels-50

A-weighted levels: Large-sized vehicles: Medium-sized vehicles: Small-sized vehicles: Passenger car

-40

63

125

250

500

1k

2k

(a) Dense asphalt pavement

4k

㻦 Porous asphalt
㻦 GGAM㻦 Dense asphalt
63

125

250

500

1k

2k

4k

(b) Porous asphalt pavement and GGAM

Figure 7 – A-weighted relative sound power levels in 1/3-octave bands on different types of road pavements.

4. SOUND POWER SPECTRUM OF ROAD VEHICLESThe A-weighted sound power level for each frequency band (1/n-octave band) is given by thefollowing method. For the frequency bands, the center frequencies for the 1/1-octave bands are from63 Hz to 4 kHz, and those for 1/3-octave bands are from 50 Hz to 5 kHz. The A-weighted band
power level L WA(fc,i ) for the i-th center frequency is calculated as(5)‫ܮ‬ௐ୅ ൫݂௖,௜ ൯ = ‫ܮ‬ௐ୅ + ο‫ܮ‬ௐ୅ ൫݂௖,௜ ൯
where L WA is the A-weighted sound power level of road traffic [dB] and 'L WA(fc,i) is the A-weighted
relative power level for the frequency band of fc,i [dB]. The energy synthesis value of 'L WA(fc,i) is
adjusted to 0 dB.
Figure 7(a) shows the A-weighted relative sound power levels 'L WA(fc,i) in 1/3-octave bands forfour types of road vehicles on dense asphalt pavement. It can be seen that the A-weighted soundpower levels for heavy vehicles (medium- and large-sized vehicles) are dominated by the
low-frequency components, and the maximum of the sound spectrum shifts to lower frequency thanthat for light vehicles (passenger cars and small-sized vehicles).
The comparison of the typical 'L WA(fc,i) for road traffic noise, which is calculated from L WA of3702

heavy and light vehicles, between different pavement types is presented in Fig.7(b). Regarding the
porous asphalt pavement, the peaks of the relative 1/3-octave band levels are at frequencies of 630
and 800 Hz, and the components at frequencies above 1 kHz are lower than those for the dense
asphalt pavement. On the other hand, the sound spectrum of traffic noise on GGAM is quite similar
to that on the dense asphalt pavement except for a frequency range of 2 kHz or more.

5. CONCLUSIONSThe calculation formula for the A-weighted sound power level L WA and the sound power spectrum
model of each road vehicle type have been revised in ASJ RTN-Model 2018. The main results are as
follows:(1) The category of the road vehicle types was changed from four-category classification to
three-category classification (light-, medium-, and large-sized vehicles).
(2) The calculation formula for L WA of road vehicles under steady running conditions was modified
based on newly accumulating data of pass-by noise measurements. The noise reduction relative tothe conventional dense asphalt pavement is almost 5 dB for porous asphalt pavement, and 2 dB
for GGAM, respectively.
(3) The typical sound power spectrum of road traffic noise on each type of pavement was revised. The
sound spectra for GGAM and dense asphalt pavement are similar except for high-frequency
components of road traffic noise.
(4) The sound power levels of HVs/EVs on the dense asphalt pavement are almost 1 dB lower thanthose of conventional passenger cars (GEVs) at steady running speeds over 40 km/h. The further
measurement under acceleration running conditions will be necessary to assess the noise reduction
effect by these low-emission vehicles near the intersections in urban areas.

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