Driving while intoxicated (DWI) offenses happen every day in Missouri. Sometimes, police officers notice signs of intoxication while observing traffic. Drivers who swerve, overreact to changing conditions or drive too slowly as compared with other drivers may prompt police officers nearby to initiate a traffic stop.
If they get arrested and charged with a DWI offense, a combination of their behavior at the wheel and the results of field sobriety tests and chemical tests will provide the evidence against them in court. In a small number of cases, the chemical tests will be the only actual evidence against the driver.
That individual faces a per se or administrative DWI charge.
How per se laws work
Missouri laws make it clear that it is illegal to drive a vehicle with alcohol or another substance negatively affecting your ability. Demonstrating impairment at the wheel or causing the crash after consuming drugs or alcohol will be grounds for arrest and DWI charges.
However, people can and do face DWI charges because of a technical infraction. If an officer asks whether you have had anything to drink and you admit that you have, they might request a chemical breath test despite your driving being normal.
If your breath test shows a blood alcohol concentration (BAC) over the legal limit, they will probably arrest you for a per se infraction. Having a BAC that exceeds the legal limit is a crime in and of itself even if the alcohol does not affect your driving.
For most drivers, the legal limit is 0.08%. For those under the age of 21, it is 0.02%. Those driving commercial vehicles can face a per se DWI charge with a BAC of 0.04%.
How do you defend against a per se charge?
As with any other DWI charge, there may be several different strategies available when you face a per se DWI charge. Some drivers could challenge the traffic stop by claiming the officer had no legal reason to pull them in the first place. Others might try to challenge the science behind chemical testing for the accuracy of the device.
Looking at all of your chances for a defense will give you the best opportunity of fighting back when you face DWI charges based solely on the BAC from a test in Missouri.