Drunk driving charges in Oklahoma are based on blood alcohol concentration, or BAC. Different levels of alcohol in the blood have been shown to affect driving differently, and the legal limit established across the country is currently set at .08 percent. Breathalyzer tests are used by police to measure BAC by the side of the road. Since the differences between a legal BAC and an illegal one can be small, it is important that these machines are properly calibrated. If they are not, people charged with DUI can raise that failure to maintain the equipment as part of their defense.

The Centers for Disease Control and Prevention say that driving may be affected with a BAC of as little as .02 percent. People may feel a sense of relaxation, warmth, changed mood and some loss of ability to judge. They may be less able to concentrate on two tasks at once and lose visual acuity. In addition, at a BAC of .05, the effects of alcohol become more severe. People may have some loss of muscle control that affects the ability to focus their eyes. Drivers may begin to feel especially good but also become less alert and inhibited with a weakened emergency response.

At a BAC level of .08 percent, it is more difficult for drivers to properly discern danger. People may also have less self-control and impaired reasoning skills as muscle coordination weakens in terms of vision, balance and reaction time. Drivers may be less able to control their speed, concentrate on the road or detect traffic signals.

Correctly determining the BAC level of an accused driver is critical to a DUI case. People who are facing DUI charges can work with a criminal defense attorney to challenge prosecution assertions and police evidence, including the reliability of any BAC test that was used.