In New York, as in all states, the 4th Amendment of the U.S. Constitution protects against unreasonable searches and seizures from law enforcement unless a warrant is issued. However, it is not unreasonable for the police to stop a motorist for driving under the influence of alcohol if probable cause (the reasonable belief a crime is being committed) exists. In other words, the police cannot stop your car on a whim; the officer needs a reasonable belief the law is being violated.
To make these "reasonable" beliefs, the police observe driver behavior and vehicle motions, based on factors originally determined by the National Highway Safety Administration. Specifically there a few indicators that a driver is under the influence of alcohol. These include: (1) a driver fails to stay within a lane, (2) a driver drives at a slow or excessive speed, or brakes erratically, and (3) if the motorist has judgment and vigilance problems.
The most common indicator is if there are any problems driving within a lane. These include weaving within the lane, weaving across other lanes, straddling a lane line, swerving, wide turns, drifting and almost causing a motor vehicle accident.
Speed and braking problems include problems stopping, accelerating or decelerating, and slow and excessive speeds.
Problems with a motorist’s judgment and vigilance include following other vehicles too closely, improper or unsafe lane changes, illegal or improper turns, driving on undesignated roadways, disobeying traffic signals or signs, and unusual behavior such as throwing things out of the window of the car, driving in the opposite lane, driving in the wrong direction on a one way street, driving with no headlights, slowly responding to traffic signals or stopping for no apparent reason.
If upon a police officer’s first observation of your vehicle they observe a mere traffic or equipment violation, the actual stopping of the motor vehicle in response to the police officer’s signal to stop can also give rise to probable cause a motorist may be driving under the influence of alcohol.
The signals given to a motorist to stop their car are meant to divert the motorist’s attention from just driving to now stopping and obeying the commands of law enforcement. Stopping a motor vehicle requires driving the motor vehicle to a safe place in a short time period. The police will look to see how a motorist changes lanes, signals, and turns a steering wheel while responding to their command to pull over. If the motorist flees, is slow to respond, swerves, stops suddenly without pulling over, or strikes the curb the attending police officer will develop further suspicion that one is probably driving while intoxicated.
In New York, a common defense to a case for driving under the influence of alcohol is whether the police had probable cause to stop the driver. If you are being charged for driving under the influence of alcohol and you do not believe law enforcement had probable cause to initially stop you, your attorney can challenge the stop as part of your defense. If a judge finds the police had no probable cause to stop your motor vehicle then the case against you can be dismissed.