Sobriety checkpoints have been held to be an exception to the rule that law enforcement officers need probable cause to stop and, even if brief, detain a motorist in order for the detention to be constitutional.
Normally, police obtain that probable cause through witnessing a traffic violation, witnessing driving which would indicate drunk driving, or receiving an anonymous tip that a person may be driving drunk. Only then can law enforcement stop and detain a person.
Although officers at sobriety checkpoints do not have the probable cause usually required to stop a motorist, both the United States Supreme Court and the California Supreme Court have held that checkpoints are constitutional.
In Michigan Department of State Police v. Sitz, the United States Supreme Court held that the state’s interest in preventing drunk driving was a “substantial government interest.” It further held that this government interest outweighed motorists’ interests against unreasonable searches and seizures when considering the brevity and nature of the stop.
Three years before the decision in Michigan Department of State Police v. Sitz, the California Supreme Court in 1987 decided the case of Ingersoll v. Palmer and set forth guidelines to ensure the constitutionality of checkpoints in California. Those guidelines are as follows:
1. The decision to conduct checkpoint must be at the supervisory level.
2. There must be limits on the discretion of field officers.
3. Checkpoints must be maintained safely for both the officers and the motorists.
4. Checkpoints must be set up at reasonable locations such that the effectiveness of the checkpoint is optimized.
5. The time at which a checkpoint is set up should also optimize the effectiveness of the checkpoint.
6. The checkpoint must show indicia of official nature of the roadblock.
7. Motorists must only be stopped for a reasonable amount of time which is only long enough to briefly question the motorist and look for signs of intoxication.
8. Lastly, the Court in the Ingersoll decision was strongly in favor of the belief that there should be advance publicity of the checkpoint. To meet this requirement law enforcement usually make the checkpoints highly visible with signs and lights.
Without this last consideration, motorists would not know that there was an upcoming checkpoint to turn away from. However, because checkpoints are highly visible, motorists have the ability to turn away before reaching the checkpoint.
There are no laws that require you to drive through a checkpoint. Therefore it is perfectly legal to turn away from a checkpoint. But if you do turn away from a checkpoint, be sure that you do not break any traffic laws in the process like, say, an illegal U-turn.
Remember that an officer needs probable cause to stop and detain a motorist. By committing a traffic violation in their presence, they’ll have the probable cause to stop a motorist, not for suspicion of driving under the influence, but for the violation itself. However, once the officer has the motorist pulled over for whatever violation, you can bet that the officer will “observe the objective symptoms of intoxication” whether they’re present or not.