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Just how accurate are roadside breath tests?

Over the past generation, there has been a revolution in the attitude that law enforcement takes toward those who are suspected of drinking and driving. While most people agree about the importance of maintaining sobriety behind the wheel, practices that emphasize strict penalties have come into vogue as the recommended way of curtailing this behavior. On its own, this might not seem like a problem, but what happens if one of the tests that is most relied upon to measure sobriety behind the wheel is simply inaccurate? What happens then?

That is exactly the situation the country is currently facing, because the more breath testing devices come into widespread use and the longer they remain there, the clearer their shortcomings are to both the legal community and the general public.

Why breath tests are a threat to drivers

Alcohol Problems and Solutions covers this topic extensively in a series of posts related to the science and operation of breath testing equipment, but in no post is the case made more clearly than in "Accuracy of Breathalyzers a Threat to Law-Abiding Drivers." In that article, readers are warned:

  • While these machines do analyze alcohol in the breath, they can also pick up other compounds, and their accuracy can depend on different factors.
  • Acetone in the breath is one substance that can cause a false positive, and it can be created within the body under certain circumstances, causing sober drivers to test positive for intoxicating BAC levels.
  • Temperature can also affect the readings on these instruments, which means that they will produce false results if they are not recalibrated for temperature changes.
  • hematocrit, or blood volume levels, can change the results of handheld units and larger machines both, although handheld units are more susceptible. That is because some machines assume a certain hematocrit level when in fact there is a regular range that is quite wide.

What to do

If a person is asked to take a breath test, the best option is to just do it, because implied consent laws will provide penalties for refusing. Experienced DUI and DWI attorneys will have the resources to help if a breath test reading is inaccurate, though. They will also know the range of options if that is not the case.

There is no reason for drivers to face DUI charges on their own, and having an attorney who can advocate for them often means having the ability to negotiate more with the state. People who have been charged should contact a DUI attorney today.


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  • Client was charged in federal court with the felony offense of being an illegal alien in possession of a firearm. After negotiation with the US Attorney's Office, the felony gun charge was dismissed and our client...

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