85

Estimating Material Flows of Two-wheelers in Cambodia Imported
from Asian Countries as Used Products
Genya MURAKAMI1*, Shoki KOSAI2, Jordi CRAVIOTO3,
Shunsuke KASHIWAKURA1 and Eiji YAMASUE1
1

Ritsumeikan University, Department of Mechanical Engineering, College of Science and Engineering,
1-1-1 Noji-higashi, Kusatsu-shi, Shiga 525-8577, Japan
2
Global Innovation Research Organization, Ritsumeikan University,
1-1-1 Noji-higashi, Kusatsu-shi, Shiga 525-8577, Japan
3
Institute of Advanced Energy, Kyoto University,
Gokasho, Uji-shi, Kyoto 611-0011, Japan*E-mail:rm0139kf@ed.ritsumei.ac.jp

Abstract
The increase in the demand for two-wheelers in Cambodia has led to a significant increase in the import ofused two-wheelers from Asian countries. The practical lifespan of two-wheelers newly reused in Cambodia istherefore quite short, resulting in the quick and significant generation of end-of-life vehicles. While there has
been an increase in the number of studies based on developing waste estimation models, scenarios in whichreused products are imported to a given country have not been given significant attention. A model is neededthat would account for two-wheelers imported for reuse by second and third owners in Cambodia, considering
differences in lifespan among two-wheelers. In a scenario analysis for estimating the number of obsolete
two-wheelers, both local production and import for reuse in Cambodia were considered during the period of
2010–2040. A population balance model modified for both cases was used in the scenario analysis. Throughthese analyses, it was estimated that the number of discarded two-wheelers in Cambodia in 2040 will be in therange of 754,000 to 986,000 units, which is 6.2–8.5 times more than in 2020. Strategies for waste mitigationand effective treatment for resource recycling using discarded two-wheelers in Cambodia are discussed toprovide guidelines for avoiding environmental pollution and resource dissipation.
Key words: ELV, environmental dumping, motorcycle, recycling, Weibull distribution

1. Introduction
The demand for various types of products has
increased significantly in developing countries in recent
years as a result of rapid urbanization, increased
population and changing lifestyles (Takahashi, et al.
2017).
The incremental demand for products in developing
countries has resulted in an increase in the import andexport of used products (Yoshida & Terazono, 2010).
Developed countries export large quantities of usedproducts to developing countries for the purpose of reuse(Yoshida & Terazono, 2010).
Exporting large quantities of used products todeveloping countries for further consumption contributes
to extension of the overall lifespan of products and to
improved affordability in developing countries (Curran &Williams, 2010). Among waste management approaches,
Global Environmental Research
25/2021: 085–092
printed in Japan

reuse performs well in terms of materials and energy
recovery (Lu et al., 2018).
In addition to the positive aspects of exporting usedproducts from developed countries to developing
countries, there are some notable drawbacks. Because theused products have already been used for a number ofyears in another country, the practical lifespan of these
newly reused commodities in the developing country isinevitably shorter than that of a new product. The
expected consequence of this is a rapid increase in thenumber of obsolete products in developing countries in a
relatively short time frame.
It should be noted that because the current capacityof recycling facilities in developing countries is not
sufficient to enable the proper treatment of obsolete
products, the disposal of used products in these countries
inevitably leads to environmental pollution and resource
dissipation (Hoang et al., 2019). Since sustainable2021 AIRIES86G. MURAKAMI et al.

management policies for obsolete products are developedon the basis of estimated waste volume (Kumar et al.,2017), it is important that the waste volumes indeveloping countries be estimated and that projections be
made for the future.
While the demand for various types of products has
increased, the global increase in road transportation has
led to a massive demand for on-road vehicles. Along with
the increase in demand for road transportation, thenumber of end-of-life vehicles (ELVs), including cars andmotorcycles, is expected to increase continuously.
The number of ELVs generated in a number ofcountries has been estimated, with studies published for
China (Hu and Kurasaka 2013), Japan (Tasaki et al.,2001), Belgium (Inghels et al., 2016), and Taiwan (Lin etal., 2018). Collecting data for ELVs is relatively easy indeveloped countries because the number of ELVs isrigorously managed by vehicle registration systems (Yanoet al., 2014). On the other hand, in many developing
countries, ELVs are not properly managed due toinadequate registration systems, which makes itchallenging to monitor the number of ELVs (Duc et al.,2013). Given that the demand for vehicles is expected toincrease and appropriate recycling systems and strategies
have yet to be well established, estimating the number of
ELVs is important in developing countries. Kurogi et al.
(2021) focused on the case in Vietnam, although theirstudy did not estimate the number of ELVs consideringthat the on-road vehicles had been already used for someyears in their country of origin.
Particularly in Asian developing countries such as
Cambodia, the penetration rate of two-wheelers isextremely high for a number of types of vehicles (Truong& Ngoc, 2020). In this study, “two-wheelers” are defined
as two-wheeled vehicles powered by a motor with nopedals. Cambodia is known to have started importing usedproducts like second-hand two-wheelers and engines a
few decades ago (Chanthy & Vilas, 2011). According to
BMI Research, from January to June 2020, Cambodia
imported 180,590 two-wheelers worth $99 million (B2B
CAMBODIA, 2020). Because the two-wheelers had
already been used for some years in their country oforigin, the practical lifespans of these newly reused
two-wheelers in Cambodia were considerably shorter thanthose of new two-wheelers. Therefore, it is of interest to
the authors to estimate the number of obsolete
two-wheelers in Cambodia by considering their second
and third owners.
Thus, the objective of this study was to estimate thenumber of obsolete two-wheelers in Cambodia during theperiod 2010–2040 and design an appropriate management
plan for obsolete two-wheelers generated in Cambodia.
This study is structured as follows: In Chapter 2, themethodology is presented for analyzing the lifespan of
two-wheelers domestically produced in Cambodia andimported from other countries and estimating the numberof two-wheelers discarded among obsolete two-wheelers
in Cambodia. Chapter 3 focuses on the number ofobsolete two-wheelers for the period 2010–2040 in
Cambodia, based on three scenarios. The appropriate
treatment of obsolete two-wheelers in Cambodia from theperspective of intermediate treatment and final recycling
is discussed in Chapter 4. Finally, this study is concluded
in Chapter 5.

2. Methodology
2.1 Flow of Two-wheelers to Cambodia from OtherCountries in Southeast Asia
It is necessary to grasp the flow of two-wheelers usedin other countries and exported to Cambodia as usedproducts. In this study, data on the number of
two-wheelers imported to Cambodia were taken from UN
Comtrade (United Nations International, n.d.). UN
Comtrade is an official repository of international trade
statistics．The flow of two-wheelers registered in UN
Comtrade covers both new and used two-wheelers withno distinction made between them. This study used dataon their import to Cambodia from other countries inSoutheast Asia from 2000 to 2019.
2.2 Lifespan Estimation
2.2.1 Definitions
The definition of product lifespan varies in theliterature depending on the system employed in the
research (Oguchi et al., 2010). Murakami et al. (2010)
summarized
product
lifespanusing
different
terminologies.
This study applied two terminologies relevant toproduct lifespan. The first terminology is “domestic
service lifespan” for both two-wheelers produced
domestically in Cambodia and new imported
two-wheelers. The domestic service lifespan was definedas the duration of time from the point when the owner isfirst in possession of the two-wheeler until the moment it
is discarded by its final owner and is channeled fortreatment and recycling. The second terminology is“extended service lifespan.” This is used to refer totwo-wheelers imported from other countries. The
extended service lifespan is defined as the duration fromthe point when the 2nd owner or 3rd owner is first in
possession in Cambodia until the moment when it isdiscarded by the final owner and is channeled fortreatment and recycling.
According to Tasaki, these definitions are effective
for predicting the number of obsolete products anddeveloping an appropriate management strategy for waste(Tasaki, 2006). The concept of a domestic service lifespanhas often been used in earlier studies to estimate thenumber of obsolete products (e.g., Nguyen et al., 2009;
Nguyen et al., 2017).

Estimating Material Flow of Two-wheelers in Cambodia

2.2.2 Lifespans of Two-wheelers in Cambodia
It is necessary to consider the lifespans of
two-wheelers domestically produced and imported fromother countries separately．
The lifespan of two-wheelers domestically producedin Cambodia follows the definition of domestic service
lifespan. This study applied the domestic service lifespanof two-wheelers in Vietnam, which had been reported to
be 20.3 years, to the case of Cambodia (Kurogi et al.,2021). Cambodia and Vietnam are both Southeast Asian
countries and they share a border. Although they differ
politically, they have experienced a similar process of
economic development with stable price movement(Asian Development Bank, 2011). It was therefore
considered reasonable to apply the 20.3 years that had
been determined as the domestic lifespan of two-wheelers
in Vietnam to the case of Cambodia.
To determine the lifespan of two-wheelers imported
to Cambodia, their extended service lifespan needed to beconsidered. In this study, we focused on import data fromfive countries: Vietnam, Thailand, India, China and Japan.
These five countries account for the majority of
two-wheelers imported to Cambodia, representing morethan 90%.
Another assumption made in this study was that the
duration of use by each owner in Cambodia would be
identical to those in Vietnam, China, Thailand and India.
The potential applicability of the case in Cambodia to
Vietnam was mentioned in Section 2.2.1. It is, however,reasonable that the lifespan of a motorcycle would be
different in each country. As such, an assumption wasestablished for each country based on the lifespanreported in the existing literature for that specific country.
The study by Kurogi et al. (2021) appears to be the only
study which includes a detailed discussion on the lifespanof motorcycles for each generation of owners in Vietnam
and Japan. Since the lifespan of a commodity varies
depending on GDP per capita (Kosai et al., 2020), thisstudy assumed that Vietnam, China, Thailand and India
fell under the same category as developing countries,
while Japan is considered to belong to a different category.
In practice, as seen in the similar ownership rate of
two-wheelers in Thailand and Vietnam (Bach Duong,2016), the trend of two-wheeler use in developing
countries appears to be similar. Meanwhile, the ownershipof two-wheelers in Japan differed significantly from thatin developing countries (Kurogi et al., 2021). As such, thisstudy employed the domestic service lifespan (or duration
Table 1 Average duration of each owner’s two-wheeler use in
Vietnam and Japan based on Kurogi et al. (2021).
Country
Cambodia, Vietnam,
Thailand, India,
China
Japan

First owner[years]Second owner[years]Third owner[years]

12.1

4.28

2.14

4.8

2.9

87

of each owner) of two-wheelers in Vietnam identified in
the previous study (Kurogi et al., 2021) to the case of
Cambodia, China, Thailand and India.
The average durations of ownership by each owner in
Cambodia, Vietnam, India, China, Thailand and Japan arepresented in Table 1. Despite the uncertainty under thequalitative assumption, this study at least differentiates
among categories of associated countries to some extent.
2.2.3 Estimation of Lifespan Distribution
To estimate the lifespan distribution, this study
employed the Weibull distribution function, which isconsidered to be the most suitable simulation model for
product lifespan (Wang et al., 2013). In particular, thisstudy also estimated the number of obsolete two-wheelers
considering second and third owners in Cambodia.
The Weibull distribution function for two-wheelers in
Cambodia is described in the next chapter. This model
differs slightly from existing models, in that our study
uses a modified version of the Weibull distributionfunction based on the extended service lifespan of
two-wheelers in Cambodia.
The Weibull distribution function for thetwo-wheelers domestically produced and imported fromother countries is indicated by the following equation:
𝐹 𝑦

1

1

exp

𝑅 𝑦

𝑦

∑
𝑦

𝑋

∙ 𝛤 1

1
𝛽

(3)
(4)

where 𝐹 𝑦 is the accumulated obsoletion rate of age
𝑦 where the product reaches its end of life underownership generation 𝛼, 𝑦 is the duration of use from thepoint when the two-wheeler is imported to Cambodia
from another country, 𝑋 is the duration of ownershipgeneration 𝛼 in other countries, i.e., 𝑋 is used when
there is no use of the two wheeler in another country(corresponding to a new two-wheeler imported fromanother country to Cambodia) and 𝑋 refers to theduration of the first ownership in another country(corresponding to a used two-wheeler imported fromanother country for a second ownership in Cambodia), 𝑦
is the average lifespan of two-wheelers in Cambodia, 𝛽
is a shape parameter estimated by confirming how well
the curve matches the accumulated distribution
percentage of obsolete two-wheelers. 𝛤 is a gammafunction. 𝑅 𝑦 is the survival rate of two-wheelers in
Cambodia in year 𝑦.
2.3 Predicting the Number of Obsolete Two-wheelers
The population balance model (PBM) designed by
Tasaki was used in many similar studies to predict the
number of two-wheelers (Tasaki et al., 2004). This model
has been widely used to calculate the number of obsolete
products, and it is used to explain scenarios for ELVs inmany countries (Yano et al., 2016; Tsasaki et al., 2001;
Lin et al., 2018; Yano et al., 2014; Xu et al., 2019). This
study also applied the PBM, as it describes the

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G. MURAKAMI et al.

relationship between the number of possessions, demandand disposals.
The PBM is a model for estimating the flow of
obsolete products by considering only the first owner. In
this study, the existing PBM was modified to account forthe different generations of owners.
2.3.1 New Two-wheelers Domestically Produced in
Cambodia
The PBM for two-wheelers domestically produced in
Cambodia is indicated by the following equation:
𝑁′

𝑁′

𝐸

𝑊′

(5)

where 𝐸 is the number of two-wheelers which aredomestically produced as a new product for which
demand existed in Cambodia in year t. 𝑁′ is the numberof new domestically produced two-wheelers owned in
Cambodia in year t, and 𝑊′ is the number of newdomestically produced two-wheelers which are discardedin Cambodia in year t. In this study, data from 2000 to2019 obtained from research published by Honda (Wedge
Holdings, 2017) were used for calculating the number of
new two-wheelers domestically produced, representing
demand in Cambodia in year t.
𝑊′ is calculated by the following equation:
𝑊′
𝑓′ 𝑖

𝐸
𝑅′ 𝑖

1

𝑓′ 𝑖

(6)

𝑅′ 𝑖

(7)

where 𝑓′ 𝑖 is the obsoletion rate of age i in which theend of life of a two-wheeler domestically produced inyear t is reached, and 𝑅′ 𝑖 is the survival rate in year iafter the two-wheeler produced domestically is shipped.
𝑅′ 𝑖 is calculated in Equation 4 in Section 2.2.3. Basedon the data on 𝑊′ and 𝐸 , 𝑁′ is calculated from 2000
to 2019 using the PBM.
This study assumed that the 𝑁′ of Cambodia after2020 would be on the same upward trend as that ofVietnam. Cambodia and Vietnam are in Southeast Asiaand they have experienced a similar process of economic
development with stable price movement (AsianDevelopment Bank, 2011). Since the outline of Vietnam’s
𝑁′ up to 2004 matches the outline of that of Cambodia
up to 2019, 𝑁′ is calculated by multiplying the 𝑁′ of
Cambodia up to 2019 by the rate of increase in Vietnam
since 2004. The rate of increase in 𝑁′ in Vietnam wasestimated by Kurogi et al. (2021). 𝐸 after 2020 is
calculated using the PBM based on the 𝑁′ , and 𝑁′ ,obtained.
2.3.2 Two-wheelers Imported to Cambodia
The PBM for two-wheelers imported to Cambodia is
indicated by the following equation:
𝑁"

𝑁"

𝐹

𝑊"

(8)

where 𝐹 is the number of two-wheelers imported asownership generation 𝛼 which represents the demand inyear t, 𝑁" is the number of two-wheelers imported asownership generation 𝛼 and owned in Cambodia in year t.
𝑊" is the number of two-wheelers, which are imported
as ownership generation 𝛼 and discarded in Cambodia inyear t.
The number of two-wheelers imported from othercountries which are discarded in Cambodia in year t iscalculated by the following equation:
𝐹

𝑊"
𝑓" 𝑖

𝑅" 𝑖

𝑓" 𝑖

(9)

𝑅" 𝑖

(10)

1

where 𝑓" 𝑖 is the obsoletion rate of age i in which theend of life of two-wheelers imported in year t is reached,
and 𝑅" 𝑖 is the survival rate in year i after the imported
two-wheeler is shipped. 𝑅" 𝑖 is calculated in Equation
4 in Section 2.2.3. Based on the data on 𝑊" and 𝐹 ,𝑁" from 2000 to 2019 is calculated using the PBM.
As pointed out above regarding domestically
produced two-wheelers, for 𝑁" after 2019, it is assumed
that the number of two-wheelers imported from othercountries and owned in Cambodia will increase in thesame way as the number of two-wheelers owned inafter 2019 is calculated using the PBM
Vietnam. 𝐹
based on the 𝑁" , and 𝑊" obtained.
2.3.3 Total Number of Discarded Two-wheelers in
Cambodia
The total number of two-wheelers discarded in year t
is calculated by the following equation:
𝑊

𝑊′

𝑊"

(11)

Finally, this study estimated the number of obsolete
two-wheelers to be generated in Cambodia by 2040.

3. Results
The number of obsolete two-wheelers in Cambodia
was estimated. The results are presented in Fig. 1. This
study considered three scenarios where all two-wheelers
imported to Cambodia from other countries would be
used by first, second and third owners, in turn. That is, arandom mixture of ownership generations was notconsidered here. For instance, the scenario description“Import (1st)+Domestic production” indicates estimationof the total number of obsolete two-wheelers that had
been imported to Cambodia from other countries as new
products as well as those produced domestically in
Cambodia.
To generalize, it is estimated that the number ofobsolete two-wheelers in Cambodia will increase year by
year in all three scenarios. The estimated number ofobsolete two-wheelers drastically increases after 2020.
This is because there was an abundance of two-wheelers
imported in 2016, which have a great influence on theincrease after 2020.

Estimating Material Flow of Two-wheelers in Cambodia

Number of obsolete two-wheelers（units）

1,200,000
1,000,000
800,000

Import(1st)+Domestic production
Import(2nd)+Domestic production
Import(3rd)+Domestic production

600,000
400,000
200,000
02000 2005 2010 2015 2020 2025 2030 2035 2040

year
Fig. 1

Estimation of the number of obsolete two-wheelers in
Cambodia.

This study demonstrates the features of this trend,using the scenario “Import(2nd)+Domestic production.”
Here, all two-wheelers imported into Cambodia areconsidered used products which are used by second
owners in Cambodia. The number of two-wheelers
discarded in 2030 (approximately 0.49 million units) and
2040 (approximately 0.91 million units) is expected to be
3.4 times and 6.4 times higher, respectively, than that in2020 (approximately 0.14 million units). The number of
two-wheelers owned in Cambodia in the year 2040 is
expected to be 16,000,000 units, and the average numberof two-wheelers per capita in 2040, 0.87 units.
Based on these three scenarios, it can be said that theconceivable number of obsolete two-wheelers in
Cambodia is within the gray range in Fig. 1, with an error
range of ± 10% in the reliability of this result. Meanwhile,
this error range indicates that different ownershipgenerations for imported two-wheelers result in asignificant difference in the estimate. This suggests thatthe shorter lifespan of two-wheelers imported from othercountries shortens the disposal cycle. For instance, it was
found that the number of discarded two-wheelers in
Cambodia under the scenario of “Import (3rd) + Domestic
production” in 2040 (986,000 units) would have increased
by a factor of 1.31 compared to that under the scenario of“Import (1st) + Domestic production” (754,000 units).
In this way, the real number of obsolete two-wheelers
in Cambodia may be greater than the estimated number ofobsolete two-wheelers in Cambodia based on the existing
PBM, which does not consider different ownershipgenerations. This is a clear indication that Cambodia
urgently needs treatment measures for discarded
two-wheelers.

4. Discussion
In the previous chapter, the estimated number ofobsolete two-wheelers in Cambodia during the period up
to 2040 was presented. To address the issue of treating
significant quantities of obsolete two-wheelers in
Cambodia, it will be important to develop an appropriate

89

management strategy for two-wheelers in Cambodia.
Appropriate treatment of obsolete two-wheelers
needs to be executed in two steps: intermediate treatment
and final recycling. At intermediate treatment facilities,
obsolete two-wheelers would be manually disassembled
and crushed using a machine so that the waste could beprocessed smoothly. At the final recycling facilities, thewaste would be recycled according to how it wasclassified as a resource in the intermediate treatment
facilities. From the perspectives of intermediate treatment
and final recycling, we considered what would be
required to ensure that obsolete two-wheelers in
Cambodia are treated appropriately.
4.1 Intermediate Treatment
The current capacity for intermediate treatment in
Cambodia is not sufficient to meet the requirements forthe proper treatment of the waste from obsolete
two-wheelers (JICA, KOA SHOJI, FORVAL 2016).
Therefore, we investigated the possibility of installing anintermediate treatment facility in Cambodia.
Regarding the number of obsolete two-wheelers to beprocessed, the scenario “Import (3rd) + Domestic
production” provided in Chapter 3 was used to represent
the worst case scenario in Cambodia.
To suggest the systems required for appropriate
intermediate treatment of two-wheelers in Cambodia, afield survey was conducted at one of the formalintermediate facilities in Japan as a representative case. In
the case of the disassembling process, a facility covering
approximately 1,000 m2 of land deals with approximately
2,000 units per person per year, with 24 laborers working
fulltime. This means that 24 workers are capable ofmanually disassembling 48,000 motorcycles in one year
at a single intermediate treatment facility. Assuming that
installations with equivalent capacity to that in Japan were
established in Cambodia, a total of 21 intermediate
treatment facilities equivalent in capacity to one Japaneseintermediate treatment facility would be required by 2040
in order to disassemble the projected number of obsolete
two-wheelers in Cambodia.
Crushing machines and backhoes are used in the
crushing process. The number of crushing machinesrequired to deal with the estimated number of obsolete
two-wheelers in Cambodia in 2040 was estimated. It was
assumed that a general crushing machine with amaximum processing capacity of three tons per hour was
installed. If this crushing machine is operated for eight
hours per day on 250 days per year, 6,000 tons of obsolete
two-wheelers could be crushed by this single crushingmachine annually. Considering that the weight of thetypical two-wheeler is 73 kg, the amount of waste fromtwo-wheelers in Cambodia in 2040 was estimated at
72,000 tons. Based on these data, 12 crushing machines
will be required by 2040 in Cambodia. Considering that
21 intermediate treatment facilities will be required by

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G. MURAKAMI et al.

2040 under the perspective of the disassembly process,the installation of a single crushing machine at eachintermediate treatment facility would be sufficient in
Cambodia.
4.2 Final Recycling Facility
Landfilling is a major waste treatment method in
Cambodia (Singh, et al. 2018). At present, the appropriate
recycling systems have yet to be established. It is notconsidered likely that the necessary number of treatment
facilities can be established with the capacity to properly
treat all the obsolete two-wheelers domestically in
Cambodia by 2040. Thus, the possibility of engaging
neighboring countries for cooperation in dealing with thelarge quantity of obsolete two-wheelers must be
considered as a course of immediate action.
To consider the requirements for final recycling
facilities, we estimated the amount of waste materials
contained in the two-wheelers in Cambodia. The amountof each material contained in an obsolete two-wheeler in
Cambodia was estimated by using the estimated numberof obsolete two-wheelers in Cambodia, which was
calculated as indicated in Chapter 3, based on the data forthe composition of two-wheelers. The scenario “Import(3rd) + Domestic production", as provided in Chapter 3,
was used to demonstrate the features of the worst casescenario in Cambodia. The amounts of each material
contained in a two-wheeler were estimated by Kurogi et al.
(Kurogi, et al. 2021).
Based on these data, the amounts of waste materials
contained in a two-wheeler in Cambodia were estimated,
as shown in Fig. 2. There is more steel than any othermetal contained in a two-wheeler: the amount of steel
discarded from obsolete two-wheelers in Cambodia in
2040 is predicted to be approximately 30,000 tons. After
steel, the metal contained in the largest quantity in
two-wheelers is the aluminum alloy, ADC12.
Approximately 19,000 tons of waste ACD12 can be
expected to be generated from obsolete two-wheelers in
Cambodia in 2040. It is important to collect and recycle
these metals efficiently from obsolete two-wheelers.

Amount of material (t)80,00060,00040,00020,000

Steel
Stainless steel
Aluminum alloy
Polypropylene
Polystyrene
ABS resin
Polyuretane
Others02000 2005 2010 2015 2020 2025 2030 2035 2040
year
Fig. 2 Estimation of the amounts of waste materials
contained in two-wheelers in Cambodia under the
Scenario “Import (3rd) + Domestic production.”

Since there is more steel than any other metal
contained in a two-wheeler, we considered the case ofsteel in more depth. It is important to ensure that the steel
from obsolete two-wheelers is efficiently recycled. The
capacities of final recycling facilities for iron scrap in2019 in neighboring countries, such as Vietnam and Laoshave been confirmed (Cravioto, et al. 2021). These
capacities were compared with the amount of iron scrap
waste generated from obsolete two-wheelers in
Cambodia.
The capacity of final recycling facilities to processiron scrap wastes in Vietnam is reported to beapproximately 1,148,000 tons, and that in Laos, about
0.15 tons (Cravioto, et al. 2021). Considering there are
30,000 tons of iron scrap contained in the obsolete
two-wheelers in Cambodia, the capacities of final
recycling facilities in neighboring countries would becapable of handling the amount of iron scrap waste from
Cambodia’s obsolete two-wheelers. That is, it will bepossible for the iron scrap wastes generated from theobsolete two-wheelers in Cambodia to be properly treated
if they are delivered to the appropriate treatment facilities
in Vietnam.
As mentioned above, used products are imported into
Cambodia from neighboring countries like Thailand andVietnam. It should be stressed that these exporting
countries also need to take responsibility for dealing withthe materials in obsolete used products like two-wheelers.
An agreement will need to be made between Cambodia
and neighboring countries arranging for all of the ironscrap waste to be delivered to the appropriate treatment
facilities to ensure that these valuable materials are notwasted. In addition, an optimal transportation system
connecting peripheral countries in the ASEAN region
should be considered as part of the responsibility for
dealing with the materials of obsolete used products like
two-wheelers.
4.3 Limitations
In this study, we estimated the number of obsolete
two-wheelers to be generated in Cambodia during theperiod 2010–2040. Several limitations, however, must be
acknowledged. It should be noted that this study assumed
that the trends in the ownership rates in Cambodia andVietnam will be the same. The two-wheeler ownershiprate may decrease with the growing number of privately
owned cars and the development of infrastructure in
Cambodia, such as railways, subways and a bus system. If
the ownership rate in Cambodia decreases, it is possiblethat the number of obsolete two-wheelers will actually
decrease.
In addition, this study assumed the lifespan of
two-wheelers to be constant, whereas the practicallifespan will inevitably change with economic
development (Kosai et al., 2020). According to a study by
Kosai et al. (2020), the lifespan of two-wheelers inEstimating Material Flow of Two-wheelers in Cambodia

Cambodia is expected to become shorter in the near future.
It is necessary to develop a policy to provide an incentive
for extending the lifespan of Cambodia’s two-wheelers.
Although this study differentiates among associatedcountries in rough categories in terms of lifespan, it would
be reasonable to expect that the average duration of eachownership in Cambodia, Vietnam, India, China andThailand would actually differ. Further analysis todetermine the lifespan of two-wheelers more accurately
for each of the associated countries will also be necessary.
Moreover, though this study employed data fromgasoline-fueled two-wheelers, it is reasonable to expectthat the share of electric two-wheelers will increase in the
future. It will be necessary to consider changes in thewaste materials contained in two-wheelers in Cambodia
from this perspective. These perspectives will be
addressed in a future study.

5. Conclusion
In this study, the flow of two-wheelers to Cambodia
from other countries in Southeast Asia was estimatedusing UN Comtrade data. Then, the lifespans of
two-wheelers domestically produced in Cambodia andimported from other countries were analyzed, and lifespandistributions were determined using the Weibull
distribution for each case. The existing population balance
model was modified to account for the different
generations of owners. The number of obsolete
two-wheelers in Cambodia was estimated during theperiod 2010–2040 using the population balance model
modified accordingly to consider the reuse of
two-wheelers imported from other countries and used bysecond and third owners in Cambodia. Finally, therequirement to ensure the appropriate treatment ofobsolete two-wheelers in Cambodia was considered fromthe perspective of intermediate treatment and final
recycling.
We found that the number of discarded two-wheelers
in Cambodia in 2040 will be in the range of 754,000 to
986,000 units. Since this is between 6.2 and 8.5 times
higher than that of 2020, ensuring that obsolete
two-wheelers can be appropriately handled must be
considered a top priority issue.
Acknowledgement
This study was partly supported by research funds
from KAKENHI Grants (20K20013, and 19H04329) andfrom the Environment Research and Technology
Development Fund (S-16, JPMEERF16S11604).
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Genya MURAKAMI
Genya Murakami is a Master’s course student at
Ritsumeikan University. He obtained his
Bachelor’s Degree in Mechanical Engineeringfrom Ritsumeikan University. His area ofexpertise covers life cycle assessment and waste
management.

Shoki KOSAI
Dr. Shoki Kosai is an assistant professor at the
Global Innovation Research Organization of
Ritsumeikan University. He obtained his Ph.D. in
Energy Science from the Graduate School ofEnergy Science, Kyoto University. His areas ofexpertise cover energy security, energy policy,
industrial ecology, life cycle assessment and waste management. As of2021, he has written 27 Scopus-based articles during his career, of which
he has been the lead author of 23.

Jordi CRAVIOTO
Dr Jordi Cravioto is an assistant professor at theInstitute for Advanced Energy, Kyoto University.
He has written on topics related to the sustainable
use of energy and resources in the industrial,
residential and transport sectors of Latin America
and Southeast Asia. He is a member of Japan's
Energy and Resources Society and the Mexican Network of Energy
Poverty Studies. He holds a B.Eng. in Electro-Mechanics from Tecnológico
de Monterrey, Mexico, and a Master’s and Ph.D. in Energy Science from
Kyoto University.

Shunsuke KASHIWAKURA
Dr. Shunsuke Kashiwakura is a lecturer at the
DepartmentofMechanicalEngineering,
Ritsumeikan University. He obtained his Ph.D. in
Environmental Science from the Graduate Schoolof Environmental Science, Tohoku University. He
specializes in high-speed optical sorting and its
evaluation, especially in the area of recycling using sensors andspectroscopy. As of 2021, he has written 31 Scopus-based articles.

Eiji YAMASUE
Prof. Dr. Eiji Yamasue has been a professor at
Ritsumeikan University since 2019. He got his
Ph.D. in 2000 from the Tokyo Institute ofTechnology, Japan, in the field of materials
science, followed by an academic carrier as an
assistant professor at the Graduate School ofEnergy Science, Kyoto University, in the fields of materials science,
environmental engineering and industrial ecology. He transferred to
Ritsumeikan University in 2016 as an associate professor. During his
career, he has written 111 Scopus-based articles and 12 book chapters.

(Received 28 June 2021, Accepted 5 August 2021)