A law passed in Japan in 1992 aimed to improve urban air quality by banning vehicles that violated certain emission standards from being registered in designated areas. A new study published in Contemporary Economic Policy provides evidence that the intervention reduced emissions, contributing to air quality improvements in metropolitan regions.

The law has been controversial because of its expense to owners of non-compliant vehicles and because of its unclear benefit. The study suggests that the law led to a 3% to 6% reduction in the monthly average ambient concentration of nitrogen dioxide over more than two decades, yielding benefits equal to about US $104 million as a result of reduced mortality from asthma.

"Japan's automobile law seems to work well, but to formally evaluate the validity of the law, full cost-benefit analyses would need to be undertaken," said corresponding author Shuhei Nishitatano, Ph.D., of Kwansei Gakuin University.