Towards Clean and Sustainable Transport in Asian Cities: Lessons Learnt from Japanese Experiences

  • Yuki Kudoh


There are a variety of potential measures to be take in the transport sector to move toward clean and sustainable transport in Asian cities. Indeed, the breadth of the range of options available makes it difficult for stakeholders to identify which measure should be taken first. To confront this issue, this chapter introduces a decomposition model of transport energy consumption and the associated CO2 emissions to identify the most relevant set of measures to be taken. Lessons learnt from Japanese experiences are presented by categorizing the measures to be taken to move toward low-carbon transport in Japan using this model.


Clean transport Decomposition method Japanese cities 

6.1 Introduction

It is impossible to complete all of daily life’s socioeconomic activities in one place owing to the spatial restrictions surrounding us. We thus conduct different necessary socioeconomic activities in different places—this is what induces the demand for transport. Hence, transport can be said to form the basis of our socioeconomic activities and has become indispensable to present-day human life. It should be noted that transport is a means to an end rather than a stand-alone purpose for most people; we engage in transport to accomplish our socioeconomic activities, and shorter transport distances and times are generally favourable. It is no exaggeration to say that our efforts to develop fast, comfortable and convenient means of transport are driven by our desire to overcome the spatial distances that exist in our daily lives.

Whichever mode of transport is used, the conveyance of people and goods consumes a large amount of energy and produces a considerable amount of associated CO2 and other environmental emissions. Past trends show that transport demand and energy consumption are strongly correlated with economic growth and improvements in the quality of life. Because automobiles are responsible for a large share of transport, this sector has a large impact on both traffic demand and energy consumption. Thus, developing clean and sustainable transport requires decreases in the demand for transport by automobile, the amount of energy they consume and the amount of CO2 emissions they produce. This should be particularly key in developing economies and cities where future transport demand is forecast to continue growing steadily.

To move towards clean and sustainable transport in Asian cities, there are a variety of potential measures that could be taken in the transport sector. Indeed, the breadth of the range of options available makes it difficult for stakeholders to identify which measure should be taken first. To confront this issue, this chapter—which is based on the author’s experience researching how to decrease the environmental impacts of the transport sector—is structured as follows: First, an overview of global and Japanese trends in transport energy and CO2 emissions is presented. Then, the structure of CO2 emissions from the transport sector is analysed. This then permits systematic categorisation of the measures to be taken to move towards low-carbon transport in Japan and to add context to the presented lessons learnt for identifying potential measures.

6.2 Transport Energy and CO2

6.2.1 Global Trends

Figure 6.1 shows the global total final consumption (TFC) of energy in recent decades. Alongside economic growth and improvements in the quality of life, energy consumption by the transport sector has globally increased absolutely. For example, in 1971 transport was responsible for 23% of the global TFC of 4244 MTOE, but by 2014 this had risen to 29% of the 9425 MTOE TFC. Within the transport sector, energy consumption by road transport was responsible for 75% of the sector’s total consumption in 2014 (IEA 2016a). One notable feature of the sector’s energy consumption is its high dependency on oil in comparison to other energy-consuming sectors. Indeed, in 2014, oil was responsible for 92% of the transport sector’s TFC (94% for road transport), whereas it only accounted for 31% and 10% of consumption in the industrial and residential sectors, respectively (IEA 2016a).
Fig. 6.1

TFC of energy by sector 1971–2014. (IEA 2016a)

In terms of the global CO2 emissions, the transport sector accounted for 23% of the total emissions from fuel combustion in 2014; emissions from road transport were responsible for 75% of the transport sector’s total emissions (IEA 2016b).

6.2.2 Japanese Trends

Figure 6.2 shows recent trends in Japanese energy TFC and gross domestic product (GDP) (ANRE 2017). TFC grew steadily in line with GDP until the mid-2000s. However, the global recession in 2008 and the Great East Japan Earthquake in 2011 have led to a levelling-off and even slight decrease in TFC in recent years. The transport sector’s TFC grew from 16% of total TFC in 1973 to 23% of the total in 2014. Figure 6.3 shows the correlation between the transport sector’s TFC and GDP (ANRE 2017). Regarding passenger transport, TFC initially increased more rapidly than GDP but has been decreasing since 2002. This change was mainly caused by increased penetration of more fuel-efficient vehicles into the fleet of passenger vehicles. In terms of freight transport, TFC began declining in 1997 because of shrinking demand, improved vehicle energy efficiency and a shift away from road transport towards other transport modes.
Fig. 6.2

Trends in TFC of energy and GDP in Japan 1973–2014. (ANRE 2017)

Fig. 6.3

Trends in TFC of energy and GDP in Japan 1973–2014 normalised to 1973 value. (ANRE 2017)

The CO2 emissions from the transport sector accounted for 17% of the national emissions (MoE 2017). Within the sector, Fig. 6.4 shows that 90% of transport-related CO2 emissions were attributed to road transport.
Fig. 6.4

Structure of CO2 emissions from transport in Japan 1990–2014. (MoE 2017)

6.3 Towards Decreased Transport Energy and CO2 Emissions

6.3.1 Decomposition of Transport Energy and CO2 Emissions

In the IPCC’s Special Report on Emissions Scenarios, the so-called Kaya identity (an equation to decompose GHG emissions into their main responsible factors) played an important role in developing future emissions scenarios (IPCC 2000). Adopting the same manner here, the energy consumed by transport and the associated CO2 emissions can be expressed using a six-level decomposition model (Matsuhashi et al. 2007), as shown in Eq. (6.1).

$$ {\displaystyle \begin{array}{c}{\mathrm{CO}}_2=\mathrm{Traffic}\ \mathrm{service}\times \left(\mathrm{Transport}\ \mathrm{distance}/\mathrm{Traffic}\ \mathrm{service}\right)\\ {}\times \sum \limits_{\mathrm{Transport}\ \mathrm{mode}}\mathrm{Share}\times \left\{\left(\mathrm{Driving}\ \mathrm{distance}/\mathrm{Transport}\ \mathrm{distance}\right)\right.\\ {}\left.\times \left(\mathrm{Energy}/\mathrm{Driving}\ \mathrm{distance}\right)\times \left({\mathrm{CO}}_2/\mathrm{Energy}\right)\right\}\end{array}} $$
The factors on the right-hand side of the equation are explained as follows:
  • Traffic service refers to the frequency at which a consumer uses an energy-consuming transport mode. One measure to decrease this factor is mode-shifting to realise a greater proportion of transport by modes that do not use external energy sources, such as walking or cycling. Another measure is decreasing the number of trips taken, perhaps by completing activities in one location or by using information and communication technologies.

  • The transport distance per traffic service term represents the distance moved to satisfy the traffic service. Examples of strategies to decrease trip length include improving land-use efficiency in cities and promoting the use of nearby facilities over those that are more distant.

  • The share of each mode of transport is also important, because decreasing the energy consumed by transport and the associated CO2 emissions can be effected by increasing the share of more energy-efficient transport modes or those that have a lower carbon intensity. For example, this could involve shifting trips from cars and planes to trains, buses and ships.

  • Driving distance per transport distance expresses how efficient the mode of transport is at conveying people and goods from one place to another. Increasing the average number of passengers or the amount of freight carried can decrease the distance to transport people and goods as a total.

  • Regarding energy consumption per driving distance, a more energy-efficient transport mode will require less energy to be consumed.

  • Improving the CO2 emissions factor of transport energy could involve the use of low-carbon electricity (from renewable sources or from fossil-fuelled power stations equipped with CO2 capture and storage technologies), biofuels or other alternative energy sources that have a lower carbon content than conventional transport fuels.

The decomposition model indicates that substantially decreasing CO2 emissions from transport can be effectively carried out by undertaking various measures simultaneously. Indeed, it would be difficult to drastically decrease CO2 emissions by taking measures in only one factor, but a decrease in each factor of 10–20% could together decrease CO2 emissions from transport by 47–74%. However, the effectiveness of any changes made to each factor strongly depends on the existing regional transport profile. Thus, notable decreases in CO2 emissions are more likely following the implementation of region- or city-specific measures.

6.3.2 Towards Low-Carbon Transport

The transport decomposition model expressed in Eq. (6.1) highlights that there are many factors that affect the transport sector’s energy consumption and CO2 emissions. Moreover, for each factor there are various candidate measures that could be taken to lower the sector’s CO2 emissions. However, such a breadth of options can make it difficult to identify the most relevant set of measures. In terms of decreasing CO2 emissions from road transport, the most prominent measure is to improve the technology used in the vehicle powertrains to shift the energy source from oil-derived fuels to low-carbon energy sources. However, other measures can also play an important role in decreasing CO2 emissions from the transport sector. These include efforts to decrease traffic by managing the demand for road transport, to decrease energy consumption by improving vehicle energy efficiency, and spatial planning at various scales to realise more convenient styles of life and work that require fewer transport services. Technological Measures

In the near term, technological innovations that improve fuel economy and increase the availability of low-carbon vehicles are the most promising options to decrease energy use and CO2 emissions from road transport. A recent growth in awareness of environmental issues has attracted attention to fuel-efficient vehicles. The overall trend in the powertrains used in road vehicles is away from conventional internal combustion engines (ICEs) towards electric motors. As part of this trend, hybrid vehicles (HVs) that have both an ICE and an electric motor have become popular in the passenger vehicle market. Plug-in hybrid vehicles (PHVs) and battery electric vehicles (BEV) that can be charged by the electricity grid are expected to be mass produced in the near future. Fuel cell vehicles (FCV), which drive an electric motor using electricity generated from a fuel cell, are another option for decreasing energy consumption and CO2 emissions in the road transport sector.

However, it should be noted that the ability of these electric vehicles (HVs, PHVs, BEVs and FCVs) to decrease CO2 emissions from conventional ICE vehicles differs according to their location. Figure 6.5 shows the relationship between the average velocity of different vehicles and their life cycle (well-to-wheels) CO2 emissions. The calculation was based on the Japanese energy supply from 2000 to 2010. Three hydrogen pathways were assumed: hydrogen from steam reforming of natural gas, by-product hydrogen of coke oven gas and hydrogen produced by water electrolysis using grid electricity. One advantage of using electric motors is their high-energy efficiency and the ability to recover energy when the vehicle slows down (regenerative braking). Figure 6.5 shows that when the average velocity is low, as in the case of travelling in traffic-congested cities, a large amount of CO2 emissions can be avoided by using an electric vehicle instead of a gasoline vehicle (GV). However, as the travel velocity increases, the ability of electric vehicles to decrease CO2 emissions compared to those from GVs decreases. Moreover, the ability of FCVs to decrease CO2 emissions strongly depends upon the hydrogen production pathway.
Fig. 6.5

Variation in well-to-wheels CO2 emissions with average travel velocity for different powertrain technologies. (Matsuhashi et al. 2007)

Another important aspect to consider is the range of the vehicles, which can be approximated by the amount of energy that can be carried on the vehicle (vehicle tank or battery). Figure 6.6 presents the energy densities of various automotive energy sources. Because the energy density of batteries is between one-tenth and one-hundredth of that of other energy sources, the range of BEVs is considerably less than that of other electric vehicles and GVs.
Fig. 6.6

Energy density of different automotive fuel types

In most Japanese cities, public transport systems are well developed, and citizens can satisfy their transport demand by short trips that do not require the use of cars. Conversely, in rural Japan cars play an important role in day-to-day transport services where transport distance also tends to be longer. For wide uptake of FCVs or BEVs, novel energy-charging infrastructure (hydrogen stations for FCVs and rapid-charging stations for BEVs) needs to be developed.

Therefore, the appropriate engine technology for low-carbon car transport may differ between cities and rural areas. Various types of electric vehicle appear more appropriate in cities where average velocity is low and trip length is short. Meanwhile HVs and fuel-efficient GVs appear more suitable for rural areas where there is little congestion and trip lengths tend to be longer. Promoting the use of locally produced biofuels is another option for realising low-carbon transport in rural areas. Measures to Impact Demand for Car-Based Transport

In addition to gains expected from changes in vehicle powertrains and energy sources, it is also important to decrease the demand for trips by private car. This could be achieved via a modal shift to public transport and the implementation of mobility management policies.

It should be borne in mind that regional characteristics strongly reflect a city’s existing urbanisation and transport system. As an example, Fig. 6.7 shows the difference between road-based per capita CO2 emissions for different-sized Japanese cities and regions. The three metropolitan areas (Tokyo, Osaka and Nagoya) accounted for 50% of Japan’s population, but their combined share of the country’s total emissions from road transport was only 42%. This indication that the intensity of emissions varies between regions and cities was clearest for Tokyo and Osaka; these show half the per capita CO2 emissions of other smaller areas. This highlights that effective measures to decrease demand for road transport should be tailored to the target city or region.
Fig. 6.7

Variation of road-based CO2 emissions in Japan by location. (Matsuhashi et al. 2007)

In Japan, it is widely regarded that the public transport system should be financially independent. This is quite different in European cities where public transport is regarded as public property and where the local government financially supports the development and management of the infrastructure. The Japanese viewpoint means that public transport services are mainly operated in large cities where a sufficient level of demand is available to sustain the service. In Japanese metropolitan areas, public transport services are well developed, and per capita CO2 emissions are relatively low in these areas (Fig. 6.7). In mid-sized cities, high population densities are essential for the development and operation of public transport systems. In rural areas where it is difficult to sustainably operate public transport systems, cars have become the habitual means of transport. Moreover, a dependency on cars may increase in areas that are suffering from depopulation.

The formation of compact cities—a form of urban design that aims to create high-density and mixed-use intensified land-use area—is key to decreasing demand for car trips in mid-size cities that currently have high per capita CO2 emissions. In Japan, where the population is decreasing and ageing, it will be necessary to redesign cities for higher population densities with local amenities and assure accessibility to public services.

6.3.3 Example Low-Carbon Transport Measures

By considering potential measures to address CO2 emissions from road transport via improved technology and decreased demand, the author’s research group identified the sets of concrete measures that could be taken in Japan that are shown in Table 6.1. In Table 6.1, the columns correspond to the various factors contributing to CO2 emissions (as expressed in Eq. (6.1)) which the rows align with the different city scales (as depicted in Fig. 6.7).
Table 6.1

Examples of measures to decrease the transport sector’s CO2 emissions at different urban scales in Japan


Urban areas of metropolitan areas

Suburbs of metropolitan areas

Urban areas of local cities

Suburbs of local cities and rural areas

Making the walking distance area high density

Already completed

Redevelopment around major stations

Redevelopment around major stations

Redevelopment in city/town/village centre

Making the city high density

Redevelopment of city centre


Formation of compact city


Utilisation of public transport

Already utilised

Circular railway, park and ride


Ridesharing small vehicles

Improvement of loading capacity

Small vehicle utilisation

Small vehicle utilisation



Improvement of energy efficiency

Electric vehicle, railway

Hybrid vehicles

Hybrid vehicles

Conventional vehicles with high fuel economy

Utilisation of low-carbon energy

Electricity, hydrogen



Urban metropolitan areas were considered to already have high-density land use, and so it would be difficult to further decrease CO2 emissions by mode-shifting to walking or bicycle. In metropolitan suburbs and urban areas in smaller cities, it should be possible to form compact city areas by redevelopment around major stations or city centres. In the urban areas of smaller cities, it should be possible to sustainably operate medium-capacity transit systems, such as light-rail transit (LRT). In metropolitan areas, energy efficiency improvements could be achieved through increased penetration of electric vehicles and the effective use of regenerative braking in railway systems.

6.4 Conclusion

Discussing a pathway towards clean and sustainable transport in Asian cities, this article focused on CO2 emissions from road transport, the main contributor to energy consumption and CO2 emissions in the transport sector. After providing an overview of trends in transport-related energy consumption and CO2 emissions, the article explained various measures that could be taken to decrease CO2 emissions using a six-level decomposition model. The six factors covered impacts on the powertrain technology employed and the demand for road-based trips. From a technological standpoint, shifting from ICEs to electric motors could notably decrease CO2 emissions. Regarding demand for road-based trips, moving towards a compact cities design in mid-size cities is key to mitigating CO2 emissions from road-based transport.

It is possible to drastically decrease CO2 emissions by addressing either technological or demand aspects individually, but placing such weight on these measures alone may be unfeasible. Stakeholders keen on developing a clean and sustainable transport sector should weigh up the option while considering individually the existing transport profile of a target region or city and the needs of the people living there. Any enacted policies should therefore be tailored to each city or region. Moreover, long lead times are likely necessary for both the robust development of a low-carbon supply chain and to support infrastructure for novel automotive technologies and to implement changes in urban systems to decrease demand for road-based transport. It is therefore important that stakeholders share with local citizens their development plans and long-term vision of achieving clean and sustainable transport.


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Copyright information

© Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.National Institute of Advanced Industrial Science and TechnologyTsukubaJapan

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