7.1 Breath and Blood Analysis

• Library: Defense of Serious Traffic Cases in Virginia (Virginia CLE) (2022 Ed.)

7.1 BREATH AND BLOOD ANALYSIS

7.101 In General.

Proof of alcohol impairment often turns on scientific evidence. The Commonwealth's case for establishing the probability of impairment usually depends on several types of sobriety tests given at the scene. These tests include (i) standardized field sobriety tests, which are "divided attention" tests that enable an officer to extrapolate alcohol impairment; (ii) chemical field tests that detect and measure alcohol (also known as preliminary breath tests or PBTs); and (iii) chemical blood or breath analysis. Practitioners must understand the science and assumptions behind these tests to assure their validity and understand the steps and procedures used to administer them in order identify flaws in their administration. Practitioners should also identify potential constitutional challenges to the admissibility...