Although having people in your car when you have been drinking is a sure way to create unnecessary distrcations, the silver lining is that these passengers are present during the initial DUI investigation and can therefore testify with personal knowledge about certain facts. Good attorneys will attempt to use these “witnesses” to testify to things like: probable cause to pull you over, conditions of the field sobriety tests, and how the tests were administered.
The California Code of Regulations lays out all the standards by which the field sobriety tests and breathe, blood, or urine samples should be collected. As part of these guidelines, each test must be administered under a strict set of circumstances. Things like lighting, uneven footing, loose gravel, or an incline can often timed invalidate an otherwise legitimate field sobriety test.
Often times the police report contends that the tests were performed flawlessly, that the conditions of even flooring and lighting were ideal, and that no conditions exist which would interfere with the test being valid. However, think about where you usually get pulled over. Usually it’s a dark road, seldom flat, maybe even a dimly lit dirt parking lot. If you have no witnesses to these conditions you could be involved in a he said she said situation when it comes time for trial. If anything, witnesses can help to corroborate your contentions and possibly assist in supporting your arguments to suppress these field sobriety tests.