A pretextual traffic stop is when a cop stops you for a minor traffic offense so that they can then investigate you for some other worse offense that they don't have evidence for yet.
For example, a vehicle momentarily crosses the center line (or is traveling at 1 mph above the speed limit, or has a broken or dim tail light, or has a license plate cover, or has windows that may be tinted beyond the limits allowed by statute, or whatever), and is stopped by a police officer. The officer interacts with the occupants of the car and develops probable cause to suspect a crime is or has been committed (this interaction to develop probable cause can be as minor as smelling something when the windows are rolled down). The officer ends up searching the car. The driver is arrested for DUI (or drug possession or trafficking or whatever more serious offense).
Why do the police do this?
This is considered effective law enforcement. The police suspect (or have profiled) your vehicle based on criteria that do not give them probable cause to detain or arrest you for the crime they suspect you of. So they follow you around until you commit some minor traffic offense. Then they stop you. And search you. And arrest you for the serious offense that they wanted to check you out for in the first place.
It is not uncommon that the traffic offense is never even charged or that the DA is willing to drop the traffic charge during plea negotiations.
Isn't profiling illegal?
Noy. In Whren v. United States, 517 U.S. 806 (1996) the United States Supreme Court unanimously ruled that a police officer's subjective (personal) reason for a traffic stop was not a factor in determining whether a traffic stop was unlawful as long as the officer had a reasonable suspicion that any criminal violation, including any sort of minor traffic infraction, had taken place.
In Whren. two vice cops (not traffic cops) in an unmarked car had a hunch about a vehicle and its occupants and decided to watch the vehilce. They initiated a traffic stop when it failed to signal before a turn and accelerated at an unreasonable speed. During the stop they found drugs and arrested the passengers. The cops admitted in court that they stopped the vehicle because they suspected the occupants were involved in the drug trade but had no actual evidence of drug possession or dealing. The Supreme Court ruled that didn't matter as the traffic infraction justified the stop in the first place regardless of the cops' personal reasons for actually conducting the stop.
What can you do about it?
- Don't commit traffic offenses. This is harder than it sounds as there are many laws on the books. However, if you haven't committed a traffic offense then, when the police stop you anyway, you are more likely to defeat a criminal charge arising from the stop.
- Make sure your car is in good visible condition. A junker is more likely to be stopped than a car in good shape.
- Don't give the police permission to search your vehicle. Ask if you may leave. The police are only allowed to keep you for as long as it takes to reasonably investigate the offense for which you were stopped (i.e. issue a ticket and check you for warrants). If they don't find a warrant or probable cause to further detain you after the traffic stop then they are supposed to let you leave and, if they do not do so, a criminal charge arising from the unlawful further detention is easier to defeat. However, if you verbally give them permission to conduct further searches (and this happens all the time), then they can keep you as long as they need to conduct their search, have their dogs sniff the car, etc.
- Don't tell the police anything other than you name and that yes you agree to show up to court to resolve your traffic ticket. Provide your license and proof of insurance when requested. Don't talk any more talk than necessary to do that. Be polite, but remember you're not under any obligation to chit chat.
- If you do these things you are much less likely to become the victim of a pretextual traffic stop. It'll save you (and the cops) a lot of hassle in the end.