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Effect of a cognitive test at license renewal for older drivers on their crash risk in Japan

Objective To evaluate the effect of adding a cognitive test to a license renewal procedure for drivers aged 75 years or older in reducing their motor vehicle collisions (MVCs). The test has been obligatory since June 2009. Methods Using monthly police-reported national data on MVCs from January 2005 through December 2016, we calculated the rates of MVCs per licensed driver-year by sex and age group (70–74, 75–79, 80–84 and 85 years or older) for each month together with the ratios of MVC rates of drivers in the three oldest age groups (which are subject to the test) to those of the 70–74 years group (not subject to the test) to control for extraneous factors affecting MVCs over the study period. Then, we conducted an interrupted time-series analysis by regressing the rate ratio stratified by sex and age group on the number of months from January 2005, June 2009 (when the cognitive test was introduced to a license renewal procedure) and June 2012 (when all drivers subject to the test have taken it at least once). Results The rates showed a longitudinal decrease in male and female drivers over the study period without any apparent effects of the introduction of the cognitive test while no significant decrease was observed in the rate ratios after the introduction of the cognitive test. Conclusions There were no clear safety benefits of the cognitive test for drivers aged 75 years or older to reduce their MVCs.