The three tests
Horizontal gaze nystagmus. The officer moves a stimulus across your field of vision looking for involuntary jerking of the eye. Six possible clues. Nystagmus has dozens of causes besides alcohol, including inner ear conditions, certain medications, fatigue, and a natural variant some people simply have.
Walk and turn. Nine heel to toe steps along a line, a turn, nine back. Eight scored clues, and two of them can be recorded during the instruction phase before you take a single step. The federal training manual says the surface should be reasonably flat, dry, and non-slippery, and that people over sixty five or with certain physical limitations should not be scored on it.
One leg stand. Foot six inches off the ground, count aloud for thirty seconds. Four clues. Same surface requirements, and the same limitations for age, weight, and injury.
Where the administration falls apart
- The instruction phase is skipped or rushed, so the test scores confusion rather than impairment
- The test is run on a sloped shoulder, gravel, or a highway with traffic passing at speed
- The subject is in work boots, or heels, and never asked about footwear
- Strobing patrol lights, which affect nystagmus tracking, are left on
- Existing injuries, inner ear problems, and medications are never asked about
- The officer's own certification is expired, or the clues are recorded inconsistently with what the video shows
That last one is the reason I watch the video before I read the report. The report is what the officer remembers. The video is what happened, and they disagree more often than you would think.
Do you have to take them?
No. They are voluntary in Texas. Officers rarely volunteer that, and the phrasing they use sounds like an instruction rather than a request. You can decline politely.
Declining has consequences. It can be argued to a jury, and it will not stop an arrest if the officer has already decided. What it does is deny the State a set of scores generated by a person who was already looking for a reason.