How to Know Probable Cause in Traffic Cases

One of the most common questions asked when a law enforcement officer stops a motorist is "Why did you stop me?" Unless you were definitely speeding or know that you ran that last stop sign, it's a question you should always ask.

Instructions

Difficulty: Moderate

1. Understand what the Fourth Amendment says. The Fourth Amendment to the U.S. Constitution says "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized." This means that the state may not enter or search you or your property without a warrant issued by a judge describing the specific reason for such a search. The state is also forbidden to "seize", or take property or arrest people without a duly sworn warrant.
2. Understand what probable cause is. The concept of "probable cause" is actually a developing idea based on a history of court cases based on the Fourth Amendment freedom from warrantless search. In a series of cases, courts have attempted to define situations where the immediate threat to public safety or stopping the commission of a crime makes taking the time to apply for a warrant a major problem if the state is to stop the crime or catch the suspect. Traffic cases have provided much of the material for these cases.
3. Understand how probable cause has evolved. Obviously there were no automobiles when the Bill of Rights was written. And we need traffic laws and enforcement those laws if we expect to be able to drive to the next town for dinner and return safely to our home. Over the years, appeals courts have considered situations brought to them and declared that there are specific circumstances under which the state can search or seize an automobile and its owner.
4. Understand what the police understand. A traffic stop is a seizure. It may be done without a warrant only if a reasonable person has a reasonable suspicion that a crime is being, has been, is about to be committed. A laser gun tracking speeders is an example of the first. A station wagon stuffed with electronic game equipment in store packaging speeding down an alley within minutes of a report of a burglary in a warehouse district is an example of the second. A third situation which relies on information from the public is the most difficult to figure and has brought on whole series of cases on who--and what--the police can use as an informant.
5. Understand the "steps" to probable cause. Only with cases where the officer actually witnesses a violation (like speeding) is there probable cause to stop. Otherwise, he must be able to explain how he came to decide to stop a driver. If he has a "reasonable suspicion" that something is wrong, the officer may stop and "freeze" the situation to investigate. Or he may the car because he is concerned about the driver's health or welfare. In either case there must be something illegal going on or something that the officer sees or notices "in plain sight" before he can arrest the driver or search the car. Any stop must build in specific steps to probable cause to arrest that the officer must be able to explain to the court.

Tips & Warnings

• Terry v. Ohio 392 US 1 (1968) and many other cases that explain the concept of probable cause and its application in "warrantless" searches are available online. Use search terms like "probable cause", "Terry stop", traffic stops".
• Remember that cops have bad nights, too. You may be the first traffic stop or the thirtieth tonight. The easiest way to get a ticket instead of a warning is to be rude and abusive when the officer walks up to your window. If you question the officer, be businesslike about it and respect her responsibility to ensure your safety and the safety of others.
• There are also limits on how long a driver may be stopped or "detained" before it is considered an "arrest". If you think that an officer is keeping you at a stop too long, it's time to ask if you're under arrest and, if not, to assert your right to go on your way. It may also be time to call an attorney.
• You can challenge probable cause for any traffic stop but before you do, you should know exactly what it means and cases that are like yours. The prosecutor is used to probable cause challenges and the court has heard a million of them. If in any doubt, seek the legal advice of a qualified attorney.