What year marks the creation of the first per se DUI law?

The first per se DUI law was established in 1939, which is significant as it marked a pivotal point in legal standards concerning driving under the influence of alcohol. A per se DUI law makes it illegal to operate a vehicle with a blood alcohol concentration (BAC) over a specified limit, typically 0.08% in modern contexts. This law shifted the burden of proof onto the accused, meaning that if a driver's BAC exceeds the legal limit, they can be charged with DUI regardless of impairment evidence.

This development was essential in the evolution of DUI laws as it provided law enforcement and the judicial system with a clear, measurable criterion for determining intoxication, fundamentally changing how DUI cases were prosecuted and paving the way for subsequent regulations and enforcement practices aimed at enhancing road safety.