Among the many exceptions to the Fourth Amendment’s requirement that police obtain a warrant before conducting a search or seizing a person or their property, the “border search exception” is one of the oldest and most well-established in the law. Many exceptions to the warrant requirement are based on expediency. For example, the “exigent circumstances exception” applies when taking the time to obtain a warrant is likely to result in the loss or destruction of evidence. The right of a nation to police its own borders, on the other hand, is behind the border search exception. The exception is not without limits, of course, but the list of law enforcement activities allowed during border stops has grown over the years, and it includes drug interdiction activities that are not allowed further inside the nation’s borders. A wide variety of Texas drug seizures occur at border checkpoints like Sierra Blanca, and at other checkpoints along the U.S.-Mexico border.
As a general rule, law enforcement officials must be able to demonstrate probable cause to believe that a search will reveal contraband or evidence of criminal activity. In order to initiate a traffic stop, they must have a reasonable suspicion of some form of wrongdoing. The U.S. Supreme Court, however, has identified several situations in which law enforcement can set up checkpoints along public roadways—which result in the stopping of vehicles without probable cause or reasonable suspicion—without violating the Fourth Amendment. For example, courts have held that the public safety interest in preventing driving while intoxicated justifies checkpoints that involve a brief stop to assess whether drivers are too impaired to drive. Michigan Dept. of State Police v. Sitz, 496 U.S. 444 (1990).
Immigration officials are allowed to operate traffic checkpoints near international borders for the purpose of investigating travelers’ citizenship or immigration status. United States v. Martinez-Fuerte, 428 U.S. 543 (1976). This includes sending vehicles to “secondary inspection” areas. The Supreme Court’s ruling specifically addressed the use of checkpoints at fixed locations, like Sierra Blanca in Texas. Immigration officials operating mobile checkpoints or conducting traffic stops must meet a greater standard of reasonable suspicion.