Driving under the influence is intimately connected in popular consciousness with drinking and driving. However, impaired driving runs the gamut from legitimate prescriptions and insufficient sleep to illegal narcotics and alcohol. Many people are involved in an impaired driving accident because they did not appreciate the nature of their impairment and how it could influence their ability to operate a vehicle safely.
Driving under the Influence: the law
Driving under the influence (DUI/DWI respectively) is the crime of operating a vehicle while impaired to a level that renders the driver incapable of operating the vehicle safely and competently. Some areas of the law are devoted exclusively to preventing drinking and driving, which is responsible for the vast majority of DUI charges, DUI-related accidents, and fatalities. However, many DUI laws also accommodate driving under the influence of drugs, distractions, or even without sufficient sleep.
DUIs by the Numbers
The majority of fatal traffic accidents are caused by drivers operating vehicles under the influence of alcohol or drugs. For people aged 15 to 29, DUIs are one of the leading causes of death. According to the National Highway Traffic Safety Administration (NHTSA), alcohol related crimes cause an estimated $37 billion in damages every year.
Investigating Driving under the Influence
Officers are empowered to stop vehicles if they have “reasonable suspicion” that the driver is operating a vehicle while under the influence of alcohol or substance. The officer can rely on external factors such as swerving, erratic changes in speed, failure to signal, and other signs of impaired driving. Once the officer stops the vehicle, he may question the driver to assess if the driver is under the influence.
The two primary tools at the officer’s disposal are the blood alcohol content (BAC) measurement tool and field sobriety tests. For drinking and driving, BAC is the primary method of ascertaining guilt or innocence.
Officers are also permitted to establish “sobriety” checkpoints. Sobriety checkpoints allow police officers to stop every vehicle and briefly interview the driver for signs of impaired driving.
Drinking and Driving
The predominate method convicting drinking and driving offenses is through the BAC. The BAC is an objective measurement that calculates the blood-alcohol content in a person’s blood and renders a percentage estimating the percentage. The amount of alcohol in a person’s blood is a good measurement of how much they drank, but it does not fully capture, if and to what extent, that person is impaired.
But no state adopts that nuanced approach to drinking and driving. Instead, all states have adopted the hard rule that any BAC that is above 0.08 percent is presumptively under the influence and automatically charged with driving under the influence.
Driving under the influence of drugs
The BAC is not available for driving under the influence of drugs. Therefore, police are forced to rely on the field sobriety test. The field sobriety test is a series of “tests” that are designed to evaluate the extent to which a particular person’s coordination and ability to drive is impaired.
There is three test validated by NHTSA:
- The Horizontal Gaze Test
- The Walk and Turn Test
- The One-Leg Stand Test
The Horizontal Gaze Test involves the driver’s eyes following an object (usually a pen) that is held up to their face. The driver is required to follow the object with just his eye. The purpose of is to evaluate eye movement and reaction to the object.
The Walk and Turn Test measures a person’s ability to follow directions, remember a series of steps, and the driver’s ability to conduct both mental and physical tasks simultaneously. The walk and turn test evaluate the coordination and mental acuity of the driver.
The one-leg stand test measures a person’s balance. The officer instructs the driver to stand on one leg to evaluate the person’s balance and coordination.
There are other tests that officers may use, including:
- The Alphabet Test which involves instructing the driver to recite all or part of the alphabet.
- The Finger Count Test which requires the driver to count the fingers on their hands.
- The Finger to Nose Test which involves the driver tilting his head back, closing his eyes, and touching his index finger to his nose, alternating hands.
If based on any of these tests, the officer determines that a driver is under the influence drugs and incapable of operating a vehicle safely, then the officer may arrest and charge the driver with a DUI.
Finally, drivers are also impaired by distractions and lack of sleep. Officers are permitted to pull drivers ver who are otherwise too impaired to drive. The officer is unlikely to charge the driver with a DUI, however, reckless driving charges and other traffic violations are possible.