Several times a year, often around holidays, police in Virginia set up "sobriety checkpoints." At these checkpoints, police will stop a certain percentage of motorists (such as every sixth motorist). At these stops, police will look for signs of drunk driving. Usually sobriety checkpoint locations are determined based on statistics regarding accidents and arrests, in addition to considering the safety of both drivers and police. For example, while it may not be safe to set up a checkpoint on a highway, it may be safe enough to set up a checkpoint on an on-ramp.
The purpose of such checkpoints is both to identify and apprehend drunk drivers, as well as keep people from drunk driving in the first place. Usually, while police will say when they are setting up checkpoints, they will often not let the public know where they will set up checkpoints. This may leave some people wondering whether such checkpoints are even legal.
While usually police need a warrant in order to perform a lawful search, sobriety checkpoints are deemed to have a public safety purpose, meaning that such searches at them are usually legal, even without a warrant. However, if a person challenges a sobriety checkpoint search, two factors will be considered: the likelihood that the sobriety checkpoint will work and how intrusive it is.
Moreover, while police may think that it is to their advantage to keep the locations under wraps, according to one professor from William & Mary, disclosing the location of such checkpoints could make it so that those checkpoints are more in line with the Fourth Amendment, and would ultimately limit how intrusive they are and make any searches more lawful.
In the end though, every situation is unique. Therefore, if a person facing drunk driving charges believes he or she was subjected to an unlawful search and seizure at a sobriety checkpoint, it may be to his or her advantage to discuss the matter with an attorney, who can assess the constitutionality of the checkpoint, and provide legal advice.
Source: WYDAILY, "Sobriety checkpoints: The pros and cons of disclosing time, location," Amy Poulter and Sarah Fearing, Oct. 6, 2017