Sobriety checkpoints are temporary roadblocks on public streets or roadways, designed to catch drunk drivers and deter other potential offenders. They also exist to catch and cite others for violations of the Vehicle Code. The roadside approach was modelled on the previous success of roadside safety checks and license and registration inspections.

Sobriety checkpoints or roadblocks generally involve law enforcement officials stopping every vehicle (or, more commonly, periodic vehicles as designated by a set mathematical formula) on a public roadway. The officers then investigate whether the driver may be too impaired to drive by looking for telltale signs of intoxication, such as alcohol on the breath, bloodshot eyes, or slurred speech.

In many cases, officers might use a quick alcohol breathalyzer inspection, to test if a driver has been drinking. If the test proves positive, the driver will then be escorted to a separate area, where the officers will then proceed to conduct a more in-depth field sobriety test.

Opponents of DUI Checkpoints claim that the numbers supporting sobriety checkpoints are skewed. For example, some critics have claimed that the 5,000 DUI arrests made at checkpoints in 2008 actually only constituted a very small percentage of the total alcohol-related arrests in California that year. In fact, according to some sources, there were 215,000 total DUI arrests in California in 2008, making the number caught at sobriety checkpoints only about 2.3 percent of the total. In addition, opponents claim that sobriety checkpoints are an exceptionally expensive means of catching drunk driving offenders. Law enforcement spent approximately $14 million in federal grant money in 2008 to arrest those 5,000 individuals. There are also those who protest that sobriety checkpoints qualify as illegal searches and seizures, violating both the state and federal constitutions.

While the federal government has managed to reconcile the idea of roadside DUI checkpoints with the Constitution, some states have not been able to do so. Many states seem to disagree on whether DUI checkpoints are a legal and efficient means of catching drink-driving offenders. Though such tests are not only legal but actually used quite commonly in the state of California, other states have forbidden them as unconstitutional. Ten states – Idaho, Iowa, Michigan, Minnesota, Oregon, Rhode Island, Texas, Washington, Wisconsin, and Wyoming – have found that roadside sobriety checks violate their own state constitutions. They have all therefore outlawed DUI checkpoints for use in catching drunk drivers. Two other states, Alaska and Montana, have not outlawed checkpoints, though for other reasons they still do not use them.

Even police officers seem to have differing opinions on the effectiveness of sobriety checkpoints. Some officers have spoken out in support of DUI checkpoints, claiming that they are a highly effective means of catching drunk drivers. Others disagree, claiming that DUI checkpoints act more as an education tool, to prevent future drunk driving, than as an active means of catching current offenders. Such officers seem to feel that patrolling the roads is a more effective way of catching drunk drivers than conducting sobriety checkpoints. It is interesting to note, however, that officers on both sides generally agree that the announcement of a DUI checkpoint beforehand acts as an excellent means of deterring people from driving under the influence.

Despite the controversy surrounding sobriety checkpoints, with such staggering rates of drunk driving-related accidents, such checks are on the rise. DUI checkpoints are becoming increasingly common in the state of California. In the 2010 fiscal year, traffic safety officials declared it "the year of the checkpoint." Their unprecedented number of sobriety checkpoints last year demonstrated a special dedication to that pledge. Approximately 2,500 sobriety checkpoints were planned for 2010. In fact, police agencies ran 1,050 state-funded DUI checkpoints, just during the major holidays. That is nearly twice as many holiday checkpoints as the year before.

The Fourth Amendment to the United States Constitution states, "The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated." At a DUI checkpoint, drivers are stopped without reasonable suspicion, and may be tested without probable cause. Thus, with this seeming conflict in mind, California's DUI checkpoints are regulated by a set of strict guidelines. Police conducting checks at this points must, by law, follow certain regulations as set out by the California Supreme Court in the case, Ingersoll v. Palmer.

There are eight key rules established by the Supreme Court, which aim to balance the rights of the individual with the need to keep roads safe for the rest of society.

First of all, time and location where a sobriety checkpoint will be established must be determined by the supervisory police officers. Officers in the field, therefore, have no jurisdiction in the decision over whether to create a DUI checkpoint. This guideline exists as a key block to arbitrary and random law enforcement. It is an instrumental act for the protection of the individual's civil rights.

Second, the Supreme Courts placed limits on the power field officers have to stop drivers at DUI checkpoints. Specifically, police at sobriety checkpoints must use a neutral mathematical formula – such as every other driver, every fifth, or every tenth – to determine which drivers to stop. By taking the power of discretion in this matter out of the hands of the field officers, this guideline prevents racial profiling and ensures that members of the public are not stopped without due cause.

Police must also give primary consideration to maintaining public safety. This means that while conducting a DUI check, the field officers must, first and foremost, ensure that there is proper lighting, warning signs and signals, and clearly identifiable official vehicles and personnel. The safety of both motorists and officers on the scene takes precedence over any desire to catch drunk drivers unawares.

Fourth, locations of roadblocks are also strictly regulated. Supervisory police officers must ensure that locations chosen for DUI checkpoints are those most likely to have a high incidence of alcohol-related accidents and arrests.

In relation to the time and duration of DUI checkpoints, the Supreme Court set relatively loose guidelines. The police involved are expected to use good judgement in the planning of checkpoint operations, with reference to their efficacy and the safety of motorists. However, so long as these basic requirements are met, there are no definite rules governing the timing of a DUI checkpoint.

Next, the California Supreme Court mandated that DUI checkpoints must be established in high visibility areas. In particular, checkpoints must be positioned in areas surrounded by flashing warning lights, adequate general lighting, police vehicles, and the presence of uniformed officers. This guideline is important not only for safety reasons, but also to reassure motorists that the checkpoint has been lawfully authorized.

Similarly, police officers operating a DUI checkpoint must provide advance notice of the roadblock to the public. They are not, however, required to disclose the exact location of the checkpoint. Such publicity reduces the intrusiveness of the checkpoint, by making it less of an imposition on the personal dignity and security of motorists on the road. In addition, publicly announcing a DUI checkpoint helps to legitimize the checkpoint in the mind of the community.

Police operating sobriety checkpoints must also detain each motorist only for so long as it takes to question the driver and determine if he or she is intoxicated. Officers can take time to look for such signs as alcohol on the breath, slurred speech, or glassy, bloodshot eyes. However, if the driver shows no signs of impairment, the officer is legally bound to allow that individual to continue on their journey without further delay. If the officer does detect some signs of impairment, in that case the driver may be detained further; the intoxicated individual may be directed to a separate area for a field sobriety test.

Lastly, the California Supreme Court declared that motorists who attempted to avoid a DUI checkpoint could not be stopped and detained simply for trying to avoid the roadblock. However, if the motorist in question violates any kind of vehicle code violation or displays any signs of intoxication, it qualifies as probable cause and the driver can be held.