The Motorcycle Kuznets Curve

Consulting Fellow, RIETI

The social costs of motor vehicles: Are motorcycles dangerous?

Motor vehicles are valuable means of enhancing people's mobility and improving their quality of life. Yet motor vehicles are associated with social costs such as traffic collisions, pollution, noise, and traffic jams. Among others, traffic collisions are a particularly crucial issue which needs to be dealt with promptly. According to the World Health Organization's (WHO) "Global Plan for the Decade of Action for Road Safety 2011-2020," traffic collisions account for 1.3 million deaths every year around the world (3,000 deaths daily), and 90% of such deaths are people from low- and middle-income countries. The global road death toll is expected to increase to around 2.4 million per year by 2030 in a business-as-usual scenario. Traffic collisions not only result in physical injuries but also entail economic loss. Such economic loss is estimated to reach $500 billion annually which is comparable to the 1%-3% of the gross national product (GNP) of each country on average.

The purpose of our study is to clarify the evolution of motorcycle ownership and its impact on traffic collisions. Motorcycles are defined here as two- or three-wheeled motor vehicles including motorized scooters, mopeds, and tuk-tuks. We focused on analyzing motorcycles as they have played an important role of transportation in low- and middle-income countries in which traffic collisions have become a serious issue. Also, road fatality risks are estimated to be 30 times higher for travel by motorcycle than by passenger car (National Highway Traffic Safety Administration [NHTSA], 2012). In fact, motorcyclists account for around 23% of all road deaths (WHO, 2013b), although this share exceeds 50% in some developing countries.

We conducted various estimates based on fixed-effects models using originally constructed data for a panel of 153 countries for the period 1963-2010. We found the following three interesting results: 1) motorcycle ownership exhibits a Kuznets-style inverse-U pattern in relation with average per capita income; 2) such inverse-U pattern is more significant in countries with higher population densities; 3) there is a positive correlation between the dependence on motorcycles and national road death rates. In what follows, I will explain each analysis, and discuss policy implications drawn from the research results.

The motorcycle Kuznets curve

The biggest contribution of our study is that it is the first of its kind to show empirically the existence of the motorcycle Kuznets curve. The Kuznets curve shows that motorcycle ownership increases as countries shift from low-income to middle-income status, but subsequently decreases once they reach their peak. Figure 1 shows the regression prediction on the relations between per capita income and vehicle ownership for various vehicle types. It suggests that motorcycles per thousand people on average evolve in a shallow inverse-U manner as GDP per capita increases, with a maximum occurring at per capita GDP of $7,000. We find it especially interesting that the Kuznets curve is witnessed only in the case of motorcycles, and no "peak vehicle" GDP per capita level for cars or trucks is found. It is also significant that the motorcycle Kuznets curve is more pronounced in more densely populated countries (Figure 2). We investigated whether other variables such as the level of urbanization or a country's average temperature affect the Kuznets curve but found no significant result.

Figure 1: Relations between per capita income and vehicles ownership for various vehicle typesFigure 1: Relations between per capita income and vehicles ownership for various vehicle types
Source: Nishitateno and Burke (2014)
Figure 2: Relations between per capita income and the number of motorcyclesFigure 2: Relations between per capita income and the number of motorcycles
Source: Nishitateno and Burke (2014)

Does an increase in the number of motorcycles mean more road deaths? The answer is yes. We found that a percentage-point increase in the share of motorcycles among all motor vehicle fleets on average is associated with 0.5% more road deaths. Also, the impact is higher for travel by motorcycle than by passenger car. The results imply that motorcyclists are as vulnerable a road user as are pedestrians. The vulnerability of motorcyclists emanates from their lack of direct protection, young average age, the often minimal training and testing requirements for motorcycle use, etc. (Asian Development Bank, 2003).

What are the necessary steps to be taken by developing countries?

The "Global Plan for the Decade of Action for Road Safety 2011-2020" adopted by the United Nations General Assembly in March 2010 highlights the importance of reducing road deaths, which have been on the rise globally, as the final common goal of many countries. Various initiatives to reach the goal have been implemented at different levels. Our results indicate that developing countries, especially densely populated ones including India and Vietnam, face the prospect of an increasing number of motorcycle-related deaths over the coming years. These countries could take steps to reduce road deaths by implementing initiatives such as designing roads with separate lanes for motorcycles, mandating adequate motorcyclist helmet laws and standards, and improving training and testing of motorcyclists.

*This is a summary of "The Motorcycle Kuznets Curve" (Nishitateno, Shuhei & Burke, Paul J, 2014, Journal of Transport Geography, Elsevier, vol. 36, pages 116-123.)

April 22, 2014
  • Asian Development Bank, 2003. Road Safety Guidelines for the Asian and Pacific Region. Asian Development Bank, Manila.
  • National Highway Traffic Safety Administration, 2012. Traffic Safety Facts: 2010 Data. National Highway Traffic Safety Administration, Washington D.C.
  • World Health Organization, 2010. Global Plan for the Decade of Action for Road Safety 2011-2020. World Health Organization, Geneva.
  • World Health Organization, 2013. Global Status Report on Road Safety 2013: Supporting a Decade of Action. World Health Organization, Geneva.

April 22, 2014