The Supreme Court has recommended certain rules for DUI checkpoints to law enforcement officials with these factors in mind. One of the more important guidelines encourage the police to create exit points before the checkpoint that allows motorists to avoid them if they choose. The police are not allowed to stop someone for avoiding a checkpoint unless they independently violate traffic laws that would allow an officer to detain them. Most checkpoints will have signage in advance of the checkpoint that advise motorists that there is a checkpoint ahead. Often, agencies will notify the public of the existence of a DUI checkpoint, not only to raise awareness to it, but to give motorists a chance to avoid driving through it.
What to Expect from a Checkpoint
The police are generally discouraged from investigating other potential crimes during a DUI checkpoint. For example, the police are not allowed to look for drugs or weapons in cars under the ruse of stopping the car for a DUI checkpoint. The primary purpose of the checkpoint must always be to screen a driver for impaired driving, and if there is none, to release the driver as soon as possible.
If there appears to be drug or alcohol impairment exhibited by a driver, the driver is usually directed to another screening area where more officers can perform a more thorough DUI investigation, such as putting the driver through roadside maneuvers. If the police believe there is probable cause to arrest, they will arrest the driver and have them perform a blood or breath test, often at the site of the checkpoint.