Similar to an alcohol-based DUI, the strongest evidence in a DUI case is a blood or saliva test. It should be emphasized that these tests are voluntary and you should not take them.
An officer may also make observations of impairment in the driver. DUI charges may be based on evidence of impairment such as poor performance on the standardized field sobriety test (SFST), slurred speech, bloodshot eyes, delayed response or committing traffic violations.