Interviewer: How is it determined if a person is under the influence?
David: There has been a tremendous amount of research done by the National Highway Traffic Safety Agency, including a research project where they actually get a bunch of volunteers in a hotel for three or four days and get them drunk. Then the agency has the volunteers do field sobriety tests to get some sense as to which tests are more reliable than others.
That type of research has resulted in three tests being taught in New Hampshire at the police academy. When you arrest someone for DWI, the first test you do is the Horizontal Gaze Nystagmus test in which they are looking for basically a Nystagmus in your eyes.
The theory is that a person under the influence has tunnel vision when the trooper’s pen goes beyond 45 degrees. Also, the eye is going to have this twitching through an involuntary Nystagmus, and that is an indicator that the person is under the influence.
So, again, the first test the police are taught to do is the Horizontal Gaze Nystagmus test. There are six clues for that. The second test they are taught to do is the walk and turn test in which there are eight clues. Heel-to-toe test is what civilians call it occasionally. Then, the third test they are taught to do is the one legged stand. They have four clues they are looking for, and they score them.
The National Highway Traffic Safety Agency has concluded that these three tests properly conducted are more reliable than some of the old fashioned tests, like a finger-to-nose test or something like that.
Interviewer: Are these three tests the field sobriety tests that people may be asked to take road side when they are pulled over?
David: Yes, they are; with respect to driving under the influence. Also, there is a national consensus at this point that .08 is the limit prima facie evidence. At .08, if you are overweight, you are impaired. If you are not, you are not. It used to be .10 and sometime ago it used to be .15.
In foreign countries, Germany for example, I think they are lower like .05. With driving under the influence of drugs cases, they do not have all the research. They do not have the experts. Certainly, they do not have people capable of rendering opinions as to what blood test level of THC is impaired by marijuana. The drug cases are somewhat more difficult for the government to prove.