How do the police assess whether a driver is drunk?

On Behalf of | Apr 16, 2024 | Criminal Defense |

The police do not always know whether a driver is drunk when they perform a traffic stop. In some cases, a driver is clearly intoxicated. For others, it may not always be clear.

The police have several ways to assess whether a driver is drunk. Some of these methods are more conclusive than others. Here is what you should know:

Traffic violations and unusual driving behavior

Typically, a traffic stop happens because a driver was violating traffic laws. This could happen because they were speeding or running red lights. A driver may also show unusual behavior while driving that could indicate they are drunk, such as suddenly slowing their speed, suddenly braking or swerving between lanes.

Field sobriety tests

If it is not obvious that a driver is drunk, the police may have them perform a field sobriety test. A field sobriety test is a physical examination used to help the police identify signs of inebriation. There are three field sobriety tests:

  • Horizontal gaze nystagmus test
  • Walk-and-run test
  • One-legged stand test

A driver may fail any of these three tests by, for example, stumbling, losing focus or falling over.

Chemical sobriety tests

If the police need to gather further evidence, they may ask a driver to take a chemical sobriety test. A chemical sobriety test evaluates the amount of alcohol found in the body. These tests include:

  • Urine test
  • Blood test
  • Breath test

Urine and blood tests often need to be tested at a hospital. However, many drivers can take breath tests during a traffic stop. 

If you are stopped by the police, it can help to understand your legal rights to help ensure you are not unlawfully arrested and charged for drunk driving. 


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