In March 2017, Utah decided to lower the legal blood alcohol content (BAC) limit for drivers from 80mg per 100ml (80mg%) to 50mg% per 100ml (80mg%). This new limit, however, did not become effective until 2019. To evaluate the impact of this policy change on traffic accidents, researchers used a difference-in-differences approach, comparing data from Utah counties with those from neighbouring states, which served as controls.
The analysis focused on whether the policy change significantly affected the number of traffic accidents or the severity of those accidents. The findings indicate that the policy temporarily reduced the total number of accidents, predominantly those resulting in property damage only. This reduction raises the possibility that drivers might avoid reporting property damage-only accidents after the new BAC limit was enacted.
To further explore this potential under-reporting, the researchers examined insurance claims data. The analysis revealed no significant decrease in insurance claims or pay-outs, suggesting that the apparent decline in total accidents likely resulted from under-reporting rather than a genuine reduction in accidents. This conclusion aligns with the observed pattern that drivers might choose not to report minor accidents to avoid legal repercussions under the stricter BAC limit.
Overall, while the policy change seemed to initially lower the number of reported accidents, the evidence points to a shift in reporting behaviour rather than an actual decrease in accident frequency. This insight highlights the importance of considering potential behavioural responses when evaluating the impact of legal and regulatory changes on public safety outcomes.
