In every state, a blood alcohol level of 0.08 is the standard police use to determine if someone is driving while under the influence of alcohol. However, it was not always set at 0.08. In the past, some states had it at 1.0 or even 1.5. Some groups even insist the limit needs to go even lower to further reduce drunk driving.
With a limit in place, it is understandable some people would assume if you have a BAC less than 0.08, you will not face arrest. On the contrary, there have been instances of police arresting people for having a BAC less than 0.08.
Some groups of people must always have a BAC of less than 0.08. For instance, there is a zero-tolerance policy in place for teenagers, so if a teen has a BAC of anything other than 0.00, then he or she will face arrest. Additionally, drivers who operate commercial vehicles cannot get behind the wheel with a BAC higher than 0.04.
Police officer's discretion
Another aspect that comes into play is whether the arresting officer believes the driver is still a threat on the road even if the BAC is less than 0.08. As an example, an officer may see a driver swerving between lanes and decide to pull him over. After a breathalyzer test, the officer discovers the driver has a BAC of 0.06. While this is technically under the limit, the officer believes the driver is a danger to himself and others and places him under arrest for DWI.
Breathalyzers do not pick up other drugs, so if a driver has used marijuana in addition to drinking alcohol, then he may blow under 0.08. However, this mixture of substances can be extremely dangerous, so, similar to the example above, the police officer arrests the driver. All of these instances are legal, and they all require the driver to get in touch with a DWI attorney immediately.