DWI Detection and Standardized Field Sobriety Testing Session 7 Preliminary Breath Testing (PBT)

DWI Detection and Standardized Field Sobriety Testing

Session 7 – Phase Three: Pre-Arrest Screening

• Is a stage in DWI driver pre-arrest

screening

• Purpose: Demonstrate association of

alcohol with the observable evidence

of the driver’s impairment

• Impairment established through

sensory evidence: what officer sees,

hears, smells

• It does not indicate the level of driver

impairment

Preliminary Breath Testing (PBT)

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F. Advantages and Limitations of Preliminary Breath Testing

Preliminary breath testing, like psychophysical testing, is a stage in the pre-arrest

screening of a DWI subject. Usually the subject is not yet under arrest when requested

to submit to the preliminary breath test.

The basic purpose of preliminary breath testing (PBT) is to demonstrate the association

of alcohol with the observable evidence of the subject's impairment. The subject's

impairment is established through sensory evidence: what the officer sees, hears and

smells.

The PBT provides the evidence that alcohol is the chemical basis of that impairment by

yielding an on the spot indication of the subject's blood alcohol concentration (BAC).

The PBT provides direct indication of the BAC level. It does not indicate the level of

the subject's impairment. Impairment varies widely among individuals with the same

BAC level.

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HS 178 R5/13 17 of 26

DWI Detection and Standardized Field Sobriety Testing

Session 7 – Phase Three: Pre-Arrest Screening

• PBT conducted at investigative stage

• Accusatory stage has not yet begun

• PBT is one of many factors to determine

if driver should be arrested for DWI

• Never the sole basis for a DWI arrest

• PBT provides direct indication of alcohol

impairment

• Administer PBT after administering

SFSTs

PBT – Investigative Stage

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The DWI incident remains at the investigative stage; the accusatory stage has not yet

begun. The PBT result is only one of many factors the officer considers in determining

whether the subject should be arrested for DWI. Whenever possible, it should never be

the sole basis for a DWI arrest. The PBT result is an important factor because it

provides direct indication of alcohol impairment. All other evidence, from initial

observation of the vehicle in operation through psychophysical testing, indicates alcohol

impairment.

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DWI Detection and Standardized Field Sobriety Testing

Session 7 – Phase Three: Pre-Arrest Screening

• Corroborate other evidence

• Confirm officer’s judgment

• Confirm alcohol as cause of impairment

• Help establish probable cause for DWI

arrest

PBT Advantages

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PBT Advantages

A PBT offers several important advantages for DWI detection. It may:

• Corroborate other evidence by demonstrating that the suspicion of alcohol

impairment is consistent with the officer's observations of the subject's mental and

physical impairment.

• Confirm the officer's own judgment and help gain confidence in evaluating alcohol

impairment accurately, based on observations and psychophysical tests. (Many

officers experienced in DWI enforcement find that they rely less and less on the PBT

as their confidence in their own powers of detection increases).

• Disclose the possibility of medical complications or impairment due to drugs other

than alcohol. (The PBT can confirm or deny that alcohol is the cause of the observed

impairment. For example, observed psychophysical impairment coupled with a PBT

result showing a very low BAC indicates an immediate need to investigate the

possibility that the subject has ingested a drug other than alcohol or suffers from a

medical problem).

• Help to establish probable cause for a DWI arrest. (The role of the PBT in

establishing probable cause may be affected by the evidentiary value of PBT results

in your state. Consult your specific PBT law, your supervisor, or the local prosecutor

for clarification, if necessary).

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DWI Detection and Standardized Field Sobriety Testing

Session 7 – Phase Three: Pre-Arrest Screening

• Evidentiary

• Accuracy

PBT Limitations

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PBT Limitations

Preliminary breath testing may have both evidentiary limitations and accuracy

limitations. Evidentiary limitations vary with specific laws. In some states PBT results are

admissible as evidence; in other states they are not admissible. Where the results are

admissible, there may be differences in the weight or value they are given. Consult your

state PBT law, your supervisor or your local prosecutor, as necessary, for clarification.

Although all PBT instruments currently used by law enforcement are reasonably

accurate, they are subject to the possibility of some error, especially if they are not used

in the proper fashion.

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HS 178 R5/13 20 of 26 Source: DWI Detection and

Standardized Field

Sobriety Testing

March 2013 Edition