Abstract

Objectives: To clarify why seatbelt legislation did not achieve the expected reduction in mortality in Japan.

Location and background: Seatbelt legislation was enacted in Japan in September 1985 and penalties were introduced in November 1986.

Methods: The driver deaths per vehicle km traveled (D/VKT) were calculated to adjust for changes in traffic volume. Decreases in D/VKT were compared with the reduction expected after legislation. The association between percentage changes of driver D/VKT, seatbelt use rate, and seatbelt non-use rate were explored. Deaths of passengers, pedestrians, and cyclists were also examined. Mortality data were obtained from vital statistics, traffic volume figures from the Ministry of Land, Infrastructure, and Transport, and seatbelt use rates from the National Police Agency.

Results: Although the decrease in D/VKT after the law was enforced was larger than the absolute number of deaths, it was far less than predicted. The percentage decrease in seatbelt non-use rate showed the strongest correlation with the percentage decrease in driver mortality. Mortality did not increase among other road users after the law was enacted.

Conclusion: Accurate evaluation of the effect of seatbelt legislation must take into account changes in traffic volume. The selective recruitment hypothesis—that high risk drivers were less responsive to seatbelt legislation—fits well with the findings. There was no conclusive evidence supporting risk compensation—that is, an increase in injuries among other road users.