Division of Roles between Compulsory and Voluntary Insurance:
The Case of Japanese Automobile Liability Insurance Scheme
Takau YONEYAMA
Yoshihiko SUZAWA
Abstract
This study attempts to provide a theoretical framework of division of roles of compulsory andvoluntary automobile insurance based on an analysis of the Japanese scheme in relation to insurance
availability and adverse selection. Japanese automobile insurance is unique as it consists of two
different components: compulsory automobile liability insurance operated under tariff rates andvoluntary automobile insurance for which certain types of risk classifications are allowed. TheJapanese scheme is doubtlessly appraisable because it has successfully contributed to an availabilityof insurance coverage and avoided an increase of uninsured motorists. It is, however, still
controversial if the double-layered mechanism may increase transaction costs borne by parties
concerned including insurers, policyholders and regulators. Yet, there are not many existing works,
specific to automobile insurance, analyzing the optimal domain of compulsory and voluntary
insurances to efficiently ensure the insurance availability and to avoid adverse selection. Ourinvestigation emulates the approach of Zweifel (2000) providing implications on social and private
insurance in the life and health insurance sector from the aspect of market equilibrium, but wesubstantially expand his analytical model to compulsory and voluntary automobile insurance tobetter reflect the actual practices in the Japanese market. As a results of the analysis, we find that thedouble-layered automobile insurance system is cost-effective in minimizing adverse selection andpreserving insurance availability only when the compulsory insurance is provided at the contact
point between the fair-price line of the pooled premium and the indifference curve of low-risk
drivers, and simultaneously the voluntary insurance is offered in the exceeding area of compulsory
insurance on the risk-differentiated base.
Keywords: compulsory automobile liability insurance, voluntary automobile insurance, market
equilibrium, insurance availability, adverse selection* Takau Yoneyama is Professor of Graduate School of Commerce and Management, Hitotsubashi University, Japan. Yoshihiko Suzawa
is Associate professor of Faculty of Business Administration, Kyoto Sangyo University, Japan. Authors can be contacted bysuzawa@cc.kyoto-su.ac.jp. This study is supported by Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research(C), No. 22530467. The earlier version of this paper was presented at 2011 Annual Conference of Asia-Pacific Risk and Insurance
Association at Meiji University, Tokyo.

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