The Preliminary Alcohol Screening (PAS) is a test law enforcement uses during traffic stops to determine a driver’s blood alcohol concentration (BAC). It is usually carried out using a portable breathalyzer device on the scene. PAS tests are generally regarded as part of the field sobriety testing process and are used to create probable cause to arrest for a DUI.

This article defines PAS, explains how it works, and describes its limitations.

Key Takeaways

• Roadside breath tests, known as PAS tests, are used by law enforcement to measure a driver’s BAC during a traffic stop.
• The tests determine if officers have probable cause to arrest someone for DUI.
• In some states, PAS tests can be voluntary for drivers over 21 who are not on DUI probation.
• PAS results are generally used as a preliminary indicator and may not be admissible in court as definitive evidence.

What Is a Preliminary Alcohol Screening (PAS) Test?

Preliminary Alcohol Screening (PAS) is a breathalyzer test given at the roadside to quickly measure a driver’s BAC. Portable devices are used to conduct these tests, analyzing the alcohol content in a driver’s breath.

The PAS test is usually done during DUI investigations if the officer suspects impairment. The results help determine whether the driver’s BAC exceeds the legal limit, generally 0.08% for adults over 21, 0.04% for commercial drivers, and 0.01% for drivers under 21 in most states.

Refusing a PAS test can have consequences, depending on the driver’s age, probation status, and the state’s laws:

• Under 21 or on probation: Refusing a PAS test can cause an automatic license suspension and other penalties.
• Over 21 and not on probation: In most states, there are no penalties for refusing to take a PAS test unless refusal is part of the implied consent requirements following an arrest.

How Does a PAS Test Work?

The PAS device measures the amount of alcohol in the driver’s breath and calculates an estimate of the BAC. The process typically includes the following steps:

1. Driver consent: Participation in the PAS test may be voluntary, depending on state laws and the driver’s age.
2. Breath sample collection: The driver blows it into a mouthpiece attached to the PAS device.
3. Instant results: The device calculates and displays the estimated BAC.

PAS tests are quick and easy to administer, but their results aren't as accurate as evidentiary breath or blood tests done later in a controlled laboratory.

Limitations of PAS Tests

PAS tests have several limitations, which can affect their reliability and accuracy:

• Calibration and maintenance: Portable breathalyzer devices must be calibrated regularly for accurate readings. Incorrect results can result from improper maintenance.
• Environmental factors: Certain environmental conditions, such as temperature and humidity, can impact the accuracy of PAS devices.
• Residual alcohol: Alcohol in the driver’s mouth (from mouthwash, for example, or from recent drinking) can give falsely high readings.

As a result, PAS results are often accompanied by more accurate evidentiary tests performed at a police station or hospital.

Bottom Line

Preliminary Alcohol Screening (PAS) tests allow law enforcement officers to test a driver’s BAC at a traffic stop quickly. Although they are not always admissible as evidence in a court of law, the results have considerable bearing on probable cause for DUI arrests.

If you have been arrested for DUI, you should seek the assistance of an experienced DUI attorney. A lawyer can look at the test results to determine whether they are valid, look for defenses, and help you through the legal process.