This study investigates whether municipal mergers result in lower waste management costs. We develop a novel virtual merging method based on machine learning techniques to compile the data of the control group and estimate the effect of the large-scale consolidation in Japan on the various costs of managing municipal solid waste. We find that these mergers actually led to an increase in the total cost per ton. Estimation results also reveal that the construction cost increased in the post-merger period, which can be explained by the special bonds provided by the national government for new projects in merged municipalities. By contrast, the processing and management cost is little affected by the mergers, except for the absorption-type mergers and municipalities that never joined waste management associations. These results suggest that municipal mergers might not always bring a substantial scale economy in municipal solid waste management. Policymakers should be careful when promoting municipal mergers in the belief that a scale economy will prevail after the reform.

本研究调查市政合并是否会降低废物管理成本。我们开发了一种基于机器学习技术的新型虚拟合并方法，以编译对照组的数据，并估计日本大规模合并对管理城市固体废物的各种成本的影响。我们发现这些合并实际上导致了每吨总成本的增加。估算结果还显示，合并后的建设成本有所增加，这可以通过国家政府为合并后的城市新项目提供的专项债券来解释。相比之下，除了吸收型合并和从未加入废物管理协会的城市外，处理和管理成本受合并影响较小。这些结果表明，市政合并可能并不总能为城市固体废物管理带来实质性的规模经济。政策制定者在推动市政合并时应谨慎行事，因为改革后规模经济将占主导地位。