Are roadside breath test devices reliable?

On Behalf of | Oct 18, 2019 | dui/dwi

When law enforcement officers pull people over on suspicion of drunk driving, they often ask drivers to take a roadside breath test. Officers use breath tests to determine whether a driver has a blood alcohol content level that is over the legal limit of 0.08. The problem lies in the fact that the results from breath test devices are not always reliable, and in some cases, can lead to a wrongful DUI arrest. According to research performed by the State University of New York at Potsdam, approximately 23% of people who are tested with a roadside breath test have elevated readings, which could lead to a wrongful DUI arrest.

Breath test devices work by measuring the amount of ethanol alcohol in a driver’s exhaled breath sample. That number is converted into a blood alcohol content. When comparing the BAC levels from a breath test to those of an actual blood test, however, the numbers vary by at least 15% in some cases. Not only do breath tests measure ethanol alcohol, but they pick up other substances that have similar molecular makeup. Several factors are identified to have an impact on breath test readings, including the following:

  • Cigarette smoke and pollution in the air
  • Residual food, drink, blood or vomit in a person’s mouth
  • Fumes from gasoline or cleaners
  • Interference from law officer’s radios or cellphones
  • Relative temperature and humidity of the air

Numbers can also be altered if devices are not calibrated properly, or the law officer is using the machine wrong.