Monday – Friday 8am-6pm

Current DMV News & Articles

Authored By DMV Defense Experts

Scientific Evidence

scientific evidence dmv hearings

One of the most crucial issues at a DMV Hearing is whether or not the Department can establish that a driver’s blood / alcohol concentration was at or above the legal limit permitted for that individual’s age group.  For the most part, the DMV will rely upon the scientific analysis of a blood or breath test.  In some rare instances, a urine test may be the basis for a license suspension.  Additional items of scientific evidence may be medical or physical conditions that may affect the way a person’s body processes alcohol.  There may be scientific issues focusing specifically on how the blood / alcohol concentration in a person’s body changes over time.  There may also be issues regarding the accuracy of the device used in the testing of one’s blood alcohol concentration.  Basically, any evidence that establishes or disproves the alleged alcohol level is scientific evidence and is  relevant at a DMV Hearing.

What is the Importance of Scientific Evidence at a DMV Hearing?

As stated above the accuracy of one’s blood / alcohol concentration is a critical element of a DMV Hearing.  Also, any evidence that the DMV presents at a DMV hearing is automatically “presumed” accurate.  That’s right.  If the DMV presents evidence at a hearing, it is automatically  presumed that the evidence was collected, analyzed and evaluated properly.  That is the nightmare of a DMV Hearing.  You are presumed guilty until you prove yourself innocent.  Fortunately, the “presumption” of accuracy is a rebuttable presumption; which means, your representative is given an opportunity to demonstrate why the DMV’s evidence is not accurate or trustworthy.  The way scientific evidence is collected.  The way it is handled and stored.  The way it is tested and evaluated are all issues to be scrutinized.  Just because a blood test is “presumed” accurate doesn’t mean that it is.  Because scientific evidence is such a critical aspect of a DMV Hearing, successfully attacking that evidence can mean the difference between winning or losing.


  • Introduce New Information
  • Differentiate Yourself From the Norm
  • Provide a Stronger Defense


How We Use Scientific Evidence To Help.

Our experienced and knowledgeable team clearly understand the importance of scientific evidence.  Where and how to find it; how to develop it; and most importantly, how to present it in a format acceptable at an Administrative Hearing are key to saving your driving privilege.  During the investigative and preparatory stage of your case, we inspect every step of how your case developed and how scientific evidence may help us win your case.  In some instances, we are attacking the accuracy of the DMV’s scientific evidence; in some instances, we are introducing our own scientific evidence.  Because we understand the DMV process better than most, we know how to introduce scientific evidence in a format that will best establish the truth.

Types of Scientific Evidence for DMV Hearings

Blood Scientific Evidence

In the earliest stages of DUI investigations, police and prosecutors would arrest and prosecute drivers based largely on the observations and opinions of police officers. In the 1980’s several government studies began to correlate the direct effect of impaired drivers with the high numbers of highway deaths in the United States.

In 1938, a joint commission of the American Medical Association and National Safety Council established a .15% blood alcohol concentration as the level where the “average” person would presumably be impairedIn 1960, that very same commission published a new opinion in which the presumed level of impairment dropped to .10%. For decades, prosecutors not only had to prove that a driver had alcohol in their blood stream but that they were, in fact, impaired by that alcohol as there was no national standard which presumed impairment. Today, this standard of proof has been significantly eroded.

After several very public attacks on State Legislatures by prosecutors and Mother’s Against Drunk Driving, the Federal Government adopted the policy that any adult with an alcohol concentration of .10% or greater was automatically “presumed” impaired, regardless of the actual effects of alcohol on that individual. This “Per Se” section of the law allowed prosecutors, and the DMV, to entirely ignore the actual effects of alcohol on an individual so long as their blood alcohol concentration was above .10%. Eventually, continued pressure by prosecutors and politically active groups caused the Federal Government to drop the legal level for alcohol concentration to, the now current, .08%. This “Per Se” section of the law permits prosecutors and DMV Hearing Officers to automatically presume the impairment of a driver irrespective of their body weight, muscle mass, physical conditioning or tolerance. Simply put, everyone is drunk at .08%

Initially, several individual States resisted the reduction to such a low level, however, when the Federal Government threatened to cut-off Federal Highway Funds to those States who did not adopt the lower concentration level, all of the States in the country fell into line and today, we have the national standard of .08%.

In California, a citizen can be prosecuted for DUI, if they are impaired by any intoxicating substance, (VC Section 23152(a)), or; if their alcohol level is .08% or greater, (VC Section 23152(b)).

At a DMV Administrative Hearing, VC Section 23152(a), does not apply. While impairment issues such as driving pattern and performance of FST is entered as evidence of a lawful arrest, it is VC Section 23152(b), which enables the Department of Motor Vehicles to seize a person’s driving privilege; again presuming that “everyone is drunk at .08%.”

At a DMV Administrative Hearing, the Hearing Officer will seek to establish that the steps followed in collecting, preserving, and testing a driver’s blood were performed appropriately and that, based on that proper processing, the resulting blood alcohol concentration must be trueThis means that so long as the blood was properly tested, it must be accurate.

Classically, when a driver is arrested for DUI on a street or highway, he or she is advised of the “Implied Consent Law” and they are offered the option of submitting to a blood or breath testIn rare instances, a blood sample may be drawn at the scene by a nurse or phlebotomist who contracts with the police agency to draw blood samples from arresteesIn most instances, however, the arresting officer will transport the driver to a police station, county jail, or hospital for the blood draw

Government Codes and Regulations establish the minimum training and certification of the person who draws a blood sample. The driver’s arm should be swabbed with a “non-alcoholic” cleanser prior to the insertion of the needle. The nurse/phlebotomist is to draw a sample into a properly sealed, evidentiary test tube, which contains a certain mixture of an anti-coagulant and preservative powder. The test tube should be properly labeled to indicate the driver’s name, the date/time of draw, and the initials of the phlebotomist. In most instances, the test tube is sealed in an evidence envelope to protect its integrity and to prevent the test tube from being mixed with other samplesIn doing this, the Chain of Custody is established. At this point, the blood sample is either retained by the phlebotomist or released to the arresting officer so that it can be secured in an evidence refrigerator until it is picked up and tested by the county or state crime lab.

It is widely believed that blood analysis if the most accurate method for determining blood alcohol concentration. This belief is based upon the fact that the blood is directly tested and therefore, errors that may occur when converting testing from blood to breath are defeatedIn almost all instances, a blood sample is drawn after a driver is arrested and taken either to a police facility, county jail or hospital. The delay in time created between the time of arrest and the time of blood draw may create a defense, in that; the blood alcohol concentration of a driver, who’s blood is drawn at a police station, will reflect the alcohol level at the time of blood draw, not the time of driving.

A “time of driving” defense may be possible at the DMV, particularly if it can be shown that the blood sample was drawn from a driver more than 3 hours after the termination of driving. This may occur in arrests following an accident, where the time of the accident is not established, or when a driver is arrested at their home sometime after the termination of driving.

“Retrograde Extrapolation” occurs when a Forensic Toxicologist attempts to look back in time to calculate the actual blood alcohol level of a person “at the time of driving.” This is a difficult process that is subject to much difficulty and speculation but, presented properly, it can be a valuable tool in defending your driving privilege.

Even though blood testing is considered the most accurate method for determining blood alcohol concentration, problems do exist. Blood is an organic substance which begins to degrade the instant it leaves the human body. Hairline cracks in the test tube; lack of preservative in the test tube or, the blood sample may not have been properly mixed with the preservative; or the temperature of refrigeration can all create problems with the accuracy of blood testing. Blood samples can ferment, clot or degrade. The Gas Chromatograph used to test the blood can be faulty or out of calibration. There have even been instances where a driver’s blood is mistaken for that of a different person.

Your Representative from California Drivers Advocates will work with your Attorney or Public Defender to determine if reanalysis of your blood sample is appropriateThe review and testimony of our Forensic Toxicologist may also prove valuable.

Breath Scientific Evidence

The most frequent source of scientific evidence at a DMV Hearing is the results achieved when a driver blows into a breath device. Once a driver has been arrested, the police officer should advise the driver of the “Implied Consent” law and allow the driver to choose between a blood or breath test (urinalysis is universally not offered except in certain instances).

Invariably, drivers have a fear of needles or do not trust the sanitary conditions under which their blood will be drawn; therefore, many drivers opt to provide a breath sample.

Increasingly, California Law Enforcement Agencies are adopting the use of Evidentiary Preliminary Alcohol Screening (EPAS) devices as a means to obtain a breath sample from a driver close to the time of driving. The EPAS device is a small, hand-held, device that may be employed at the scene of the arrest, at a police substation, or a County Jail. Just like the classic “breathalyzer” in use at many police stations, the EPAS device will print out a small slip of paper (similar to a cash register receipt) which documents required information following the test. In many instances, however, the driver will be transported to a police station or county jail where they will be introduced to a larger, bench-mounted, device into which they will be directed to blow.

One of the weakest aspects of determining a person’s impairment, by either blood or breath analysis, is the presumption that every person providing a blood or breath sample is perfectly “average” in terms of their physiology.

When focusing specifically upon breath analysis, the weaknesses in these presumptions are amplified. Quite simply a breath device (whether it is an EPAS or a bench-mounted model), will see every subject as being identically average. The machine will not factor in variables such as body weight, body mass index, lung volume or metabolic rate.

To establish the correlation between alcohol present in the blood and alcohol present in the exhaled breath, a breath machine will assume a ratio of 1 to 2100. Assuming that this ratio is applicable to the “average” person, and since the machine sees every test subject as “average,” it applies the same computation of alcohol concentration whether a person weighs 130 lbs or 250 lbs. Because the machine is blind to the variables in an individual’s physiology, the readings can be wildly inaccurate.

Even more startling is the fact that breath machines DO NOT detect Ethanol (ETOH), the active compound in alcoholic beverages. Breath machines will identify ANY methyl based chemical on the breath as ETOH run a calculation on the “average” person and multiply that reading 2100 times. Thus, the machine identifies that there is a “chemical” on the breath, assumes it is alcohol, and computes a reading.

Methyl based chemicals occur naturally in the human body. Those persons suffering with diabetes may have an elevated level of acetone on the breath. Those persons practicing low carbohydrate diets may experience elevated levels of ketone on their breath. A painter who is continually exposed to paint fumes may have elevated levels of toluene in his blood stream. A mechanic who washes automobile parts in acetone may have that chemical absorbed directly through the skin into the blood stream. The tragedy here is, the breath machine will assume all of these substances are alcohol and create erroneous readings based upon its assumptions.

Based on this, a painting contractor could be on his way home from a hard day at work; be pulled over because his brake lights are not working and lose his privilege to drive because a DMV Hearing Officer believes that a breath machine correctly measured the presence of alcohol on the driver’s breath; even though he had not had one drop to drink.

Breath machines are also subject to other forms of corruption. A driver with a history of Gastro Esophageal Reflux Disease, also known as GERD, can easily corrupt an air sampleStomach vapors mixing with exhaled air from the lungs can cause the breath machine to read extraordinarily high. Drivers who have certain types of dental work in their mouth or who have a pierced tongue, can trap alcohol in their mouth which, when blown into the breath machine, can read high. Drivers suffering with asthma can have great difficulty putting enough air into a breath machine and can have “spikes” in readings because they are nearly spitting into a breath device to perform. One of the possible consequences of alcohol consumption is the driver may vomit. If this occurs within close proximity to the time of a breath sample, a result can be corrupted.

For a breath sample to be determined “reliable” there is a certain set of “building blocks” that must be in place:

  1. The testing officer must be certified in the use of the breath machine.
  2. The breath machine must be regularly serviced and calibrated.
  3. The testing officer must conduct a “continuous” observation of the driver for a period of 15 minutes, prior to the breath test, to insure the driver did not burp, regurgitate or vomit.
  4. The driver must achieve two separate readings that are within .02 of one another.
  5. The breath sample must be taken within 3 hours of the termination of driving.
  6. The officer must change the mouthpiece on the device between each consecutive blow to prevent the accumulation of alcohol in one mouthpiece.

Since the DMV will largely predicate its suspension of a driver’s license based upon the results of a breath test; the driver’s representative should conduct a thorough examination and investigation of all methods, steps, and policies employed in the collection of an air sample.

Your representative from California Drivers Advocates will carefully evaluate this information and thoroughly investigate the means by which your air samples were collectedConsideration should be given to the possibility of establishing pre-existing medical conditions that may disprove the accuracy of the samplesThis may require the testimony or declarations of doctors and/or forensic toxicologists

Urine Scientific Evidence

Although increasingly rare, a driver may be faced with a police officer’s request to provide a urine sample. On January 1, 1999, California Vehicle Code Section 23612 (a)(1)(A) was amended, such that urinalysis is no longer one of the primary chemical tests offered to drivers suspected of DUI.

Because analysis of a urine sample is classically the most unreliable of the testing procedures and because the seizing of a urine sample can be most unpleasant for police officers who would therefore, not follow proper protocols in the collection of these samples, experienced DUI attorneys and Administrative Advocates were seeing great success in attacking this type of evidence in court and before the DMV. Of course, that was not acceptable to prosecutors and Mothers Against Drunk Driving, so a tremendous lobbying effort resulted in the California State Legislature amending the vehicle code to omit urinalysis as an option for California drivers.

Today, a police officer will only request a driver to submit to urinalysis if:

  • The driver is suspected of being under the influence of a controlled substance or prescription medication.
  • The driver is suspected of being under the “combined” influence of alcohol and a controlled substance and/or prescription medication, or
  • Blood or breath testing is not readily available.

If a driver specifically asks to submit to a urine test, the request will invariably be denied; and the law now supports that.

Based on the physiology of the human body, alcohol is eliminated from the body by the kidneys. Secretions of alcohol mix with urine and are held in the bladder until being evacuated from the body through urination. It is not uncommon for a person to go hours between instances of urination and therefore, high concentrations of alcohol may be present in the bladder even though the impairing effects on the body have ceased. Additionally, a bacteria in the urinary tract known as candida albicans can actually cause a urine sample to ferment. In this instance, alcohol levels can increase in the specimen cup.

In order for a urine sample to be determined reliable, the subject driver is instructed to enter a restroom and completely void his or her bladder. The police officer should then wait for a period of 15-20 minutes and then direct the driver to re-enter the restroom and now urinate into a specimen jar. Of course, the second void should be witnessed by a police officer to insure the integrity of the specimen and to begin the “Chain of Custody.” In many instances, police officers are either not properly trained or simply ignore the process requiring the complete voiding of the bladder prior to the collection of the actual sample. If this can be demonstrated, it clearly violates provisions of Title 17, of the California Code of Regulations, and may be enough to win at a DMV Administrative Hearing.

If the DMV is your Problem...

California Drivers Advocates is your solution. We Are Here To Defend Your Driving Privilege. Contact our DMV Defense Experts here.