What is the primary way police measure BAC during a traffic stop?

The primary way police measure blood alcohol concentration (BAC) during a traffic stop is through breathalyzer tests. This method is widely used for several reasons.

Breathalyzer tests are non-invasive, quick, and can be administered at the roadside, allowing law enforcement officers to obtain immediate results. When a driver blows into the device, it measures the alcohol content in their breath, which correlates to the amount of alcohol in their blood. This correlation is based on the principle that alcohol vapor is present in exhaled breath in proportion to the amount present in the blood.

While blood tests can provide a definitive measure of BAC, they require a medical professional to draw blood and take time for analysis, making them less practical during a traffic stop. Field sobriety tests may indicate impairment but do not provide an actual BAC measurement. Urine tests, although used in some cases, are less common for immediate BAC evaluation and can be influenced by factors such as hydration and the time elapsed since alcohol consumption.

Thus, breathalyzer tests are favored in field situations due to their speed and ease of use, making them the standard approach for measuring BAC during traffic stops.