Imaginary DUI?

When police officers are attempting to determine whether to arrest someone for driving under the influence of alcohol (DUI), they usually ask them to perform some field sobriety tests.  Police generally rely on a battery of tests recommended by the National Highway Traffic Safety Administration (NHTSA).  One of these tests is referred to as the "Walk-and-Turn" test.  The instructions for performing the Walk-and-Turn test are contained in the NHTSA DWI Detection and Standardized Field Sobriety Testing Manual.

In essence, the Walk-and-Turn test requires that a person walk a straight line, touching heel to toe, and then turn around and walk back.  However, it seems many officers in Arizona (and apparently in other states as well) believe that using an imaginary line is a fair test.  That is, instead of having a person walk on a true line (i.e. a painted line in a parking lot) they have the person imagine a line to walk on.  Just this morning I was debating this issue with a Scottsdale Police Officer in a DUI case.

Austin, Texas DWI lawyer Jamie Spencer has written an excellent article entitled, Walking A Straight Line, arguing the merits of using an imaginary line during a Walk-and-Turn test.  He writes:

One common misconception that I see over and over on the part of officers, up to and including some of the local Austin DWI task force officers, is the belief that the book doesn’t require that a designated actual line be used.

If asked why the defendant was asked to walk an imaginary line instead of an actual line, most officers reply – some smugly – that ‘the manual’, that is the NHTSA manual, doesn’t require it. Some offer to show the defense lawyer exactly where in the book it says they don’t have to use an actual line.

Invariably, the officer will flip the pages and find this portion of the manual:

Procedures for Walk and Turn Testing

1. Instructions Stage: Initial Positioning and Verbal Instructions

For standardization in the performance of this test, have the suspect assume the heel-to-toe stance by giving the following verbal instructions, accompanied by demonstrations:

“Place your left foot on the line” (real or imaginary). Demonstrate.

[I’m taking this from the February 2006 Edition, Student Manual, page VIII-9 from Session VIII: Concepts and Principles of the Standardized Field Sobriety Tests. It should be in Chapter 8 of most or all other manuals.]

That certainly looks at first blush as if the manual says there’s no difference between the difficulty between walking an actual line, or walking an imaginary line. Although, it literally begs the question, “Officer, how wide a line did my client imagine?”

But no. The officer who so testifies is wrong. (Sorry, WJ, you’re wrong too.)

Flip the page once more – VIII-11 in the one I’m reading now - and you come to the part entitled:

4. Test Conditions

Walk-and-Turn test [sic] requires a designated straight line, and should be conducted on a reasonable dry, hard, level, nonslippery surface.

Requires. So, how to explain the seeming discrepancy? Easy.

The first section is talking about “Verbal Instructions” and is clearly labeled so. It is the Instructions Stage. That means… it is talking about the portion of the test where the officer demonstrates the Walk and Turn to the suspect.

So, going by the book, it’s perfectly OK for the officer to show the defendant how to do the test on his own imaginary line if he wants to do it that way. Heck, we all know they don’t even have to demonstrate all 9 steps. They are allowed to do it that way.

But the NHTSA Manual makes no bones about it: if this test is going to be administered properly, then the defendant is supposed to be afforded the opportunity to do it on an actual line. It is literally: required. And yes, that’s a potentially reasonable explanation for someone stepping ‘off the line’ – it wasn’t there in the first place.

Jamie's point cannot be overstated:  How can the officer say you stepped off a line that he cannot see?  After all, the line is in your head.  The officer does not know how long the line you imagined was; nor does the officer know how wide your imaginary line was.  Moreover, when a real line is available (such as in a parking lot), isn't it just common sense to use it during the test?  

Everyone's Blood is Not the Same

Law enforcement's primary method for determining if a person is driving under the influence of alcohol is a chemical test.  That is, a police officer will take a sample of a susect's blood  or breath.  The chemical test assumes that the composition of everyone's blood is the same.  Specifically, the test assumes that all people have the same hematocrit level.  However, this assumption is incorrect.

The hematocrit level, or packed cell volume, is a measure of the proportion of blood volume that is composed by solids.   Whole blood is composed of solid particles in liquid.  the solid portion of whole blood contains: (1) white blood cells; (2) red blood cells; and (3) platelets.  The liquid portion of the blood is known as plasma. 

In this manner, if a man has a hematocrit level of  .51, then his whole blood consists of 51% solids and 49% liquids (plasma).  This solid to liquid ratio will effect the outcome of a blood alcohol concentration test.  The reason is the liquid portion of the whole blood, the plasma, contains water.   Alcohol is more susceptible of being dissolved in water than is the solid portion.  Consequently, the liquid portion of the whole blood will have a higher concentration of alcohol than the solid portion.

Stated another way, the higher the hematocrit level (thus the less liquid) in the blood, the greater the concentration of alcohol in the liquid portion of the blood.  Ultimately this means several people with the same amount of alcohol in their body, but different hematocrit levels, will have different test results. 

Men and women have different average hematocrit levels.  A normal hematocrit for a man is 45 (plus or minus 7%). Women have a normal hematocrit level of 42 (plus or minus 5%).  There are numerous other factors that can effect a hematocrit level.  However, a person's hematocrit is not proportional to body size. 

Hematocrit ranges primarily effect breath alcohol testing. This is because in blood testing the blood is mixed with an internal standard (such as N-Propranol which has similar structure to Ethanol, but has a different number of carbons).  In sum, varying hematocrit levels expand the range of accuracy in blood alcohol concentration testing.  This expanded range of accuracy can be a valuable defense for a person accused of driving under the influence alcohol (DUI).