Roadblock

Sobriety checkpoints or roadblocks involve law enforcement officials stopping every vehicle (or more typically, every nth vehicle) on a public roadway and investigating the possibility that the driver might be too impaired to drive. They are often set up late at night or in the very early morning hours and on weekends, at which time the proportion of impaired drivers tends to be the highest. Checkpoints are also often set near the exit points of public events, to prevent large numbers of drunk drivers from being released into traffic simultaneously from the event.

With a portable and quick alcohol breath test, the police can test all drivers (if the law permits), and process the cars one by one as in a conveyor belt. When there is no quick test, a more complicated routine is necessary. Upon suspicion, the stopped driver is required to exit the vehicle and take a roadside sobriety test that requires the demonstration of both mental and balance skills. If the officer determines based on his observations during the tests, the driver is then required to take an alcohol breath test (referred to as a Breathalyzer test in the United States). It is important to note that you can not pass or fail a field sobriety test as they are not "pass-or-fail", they are only meant to aid the officer in determining if you are impaired based on observations of the subjects performance of these tests. Being subjected to perform this test is not prohibited by the fourth amendment of the United States Constitution if the law enforcement entity posts or announces in advance that these checkpoints will occur and at what location; law enforcement agencies often post a sign in a small road or street during the weekdays when it is only seen by local residents and not by those attending a special event or those that only travel in that area of the city during the weekend to patronize local bars and clubs. These announcements are also sometimes printed in news papers. Numerous websites host a database of check points that are to occur based on information found in news papers, the internet and tips from visitors of such sites.

Sobriety checkpoints regularly catch much more than just drunk drivers. The identity checks will catch individuals wanted by the police, and DUI often occurs together with other crimes, such as vehicle inspection and registration violations, vehicle tax avoidance or driving without a license.

Australia
In Australia, drivers may be stopped at any point along any road by a police officer for what police term a "random breath test", commonly referred to as an "RBT". For an operation involving a large number of police (typically 10-20) at a fixed location, the colloquial term "booze bus" is often used. In all states, the maximum blood alcohol content of 0.05% is enforced. Drivers who are found to have a preliminary reading of equal to or greater than 0.05% are required to wait for a 15 minute period, after which time they are retested.

In Queensland, Victoria and New South Wales the concept has been extended to make sobriety checkpoints also "drug buses" (or dual buses), capable of testing drivers for a number of illicit drugs including cannabis (tetrahydrocannabinol), methamphetamine, and ecstasy (MDMA).

Canada
In Ontario, Canada, sobriety checkpoints are referred to as Reduce Impaired Driving Everywhere, commonly referred to as RIDE. In Alberta and Manitoba they are referred to as Check Stop, and in British Columbia, they are known as Drinking Driving Counterattack.

Legality in the United States
The Fourth Amendment to the United States Constitution states that: “The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.” This fundamental right has a tense relationship with sobriety checkpoints. At a sobriety checkpoint, drivers are necessarily stopped without reasonable suspicion, and may be tested summarily and without probable cause. Thus the Constitution would prohibit people from being stopped without a search warrant or at least without probable cause that they have committed a crime; however, the warrant requirement only attaches should the search be unreasonable and the Supreme Court, as shown below, decided that such stops are not unreasonable under certain circumstances.

Driving under the Influence of alcohol is a special type of crime, as driving with a blood alcohol content (BAC) over a set limit is defined as the crime; it is not necessary to drive recklessly or cause an accident in order to be convicted. To determine BAC accurately, it is generally necessary for the driver to subject himself to tests that are self incriminating, and drivers sometimes exercise their right against self incrimination to refuse these tests. To discourage this, some jurisdictions set the legal penalties for refusing a BAC test to equal or worse than those for a failing a BAC test. In other jurisdictions, the legal system may consider refusing the roadside alcohol breath test to be probable cause, allowing police to arrest the driver and conduct an involuntary BAC test. The Michigan Supreme Court had found sobriety roadblocks to be a violation of the Fourth Amendment. However, by a 6-3 decision in Michigan Dept. of State Police v. Sitz (1990), the United States Supreme Court found properly conducted sobriety checkpoints to be constitutional.

In the majority opinion, Chief Justice Rehnquist wrote, "In sum, the balance of the State's interest in preventing drunken driving, the extent to which this system can reasonably be said to advance that interest, and the degree of intrusion upon individual motorists who are briefly stopped, weighs in favor of the state program. We therefore hold that it is consistent with the Fourth Amendment."

Dissenting justices argued against this conclusion. Justice Stevens argued that the checkpoints were not reasonably effective, writing that "the findings of the trial court, based on an extensive record and affirmed by the Michigan Court of Appeals, indicate that the net effect of sobriety checkpoints on traffic safety is infinitesimal and possibly negative."

Further, Justice Brennan in his dissenting opinion argued that the police had failed to show that the checkpoint seizures were a necessary tool and worth the intrusion on individual privacy. "That stopping every car might make it easier to prevent drunken driving...is an insufficient justification for abandoning the requirement of individualized suspicion," he insisted.

Jurisdictions that allow sobriety checkpoints often carve out specific exceptions to their normal civil protections, in order to allow sobriety checkpoints. Although the U.S. Supreme Court has found sobriety checkpoints to be constitutionally permissible, ten states (Idaho, Iowa, Michigan, Minnesota, Oregon, Rhode Island, Texas, Washington, Wisconsin, and Wyoming) have found that sobriety roadblocks violate their own state constitutions or have outlawed them. One other state (Alaska) does not use checkpoints even though it has not made them illegal. Montana uses checkpoints frequently. Some states combine their efforts in setting up sobriety checkpoint initiatives, such as Checkpoint Strikeforce, jointly run by Virginia, Washington DC, Delaware, West Virginia, and Maryland



Legal guidelines for checkpoint procedures
In approving "properly conducted" checkpoints, Chief Justice Rehnquist implicitly acknowledged that there must be guidelines in order to avoid becoming overly intrusive. In other words, checkpoints cannot simply be set up when, where and how police officers choose. As often happens in Supreme Court decisions, however, the Chief Justice left it to the states to determine what those minimal safeguards must be, presumably to be reviewed by the courts on a case-by-case basis.

In an effort to provide standards for use by the states, the National Highway Traffic Safety Administration subsequently issued a report that reviewed recommended checkpoint procedures in keeping with federal and state legal decisions. ("The Use of Sobriety Checkpoints for Impaired Driving Enforcement", DOT HS-807-656, Nov. 1990) An additional source of guidelines can be found in an earlier decision by the California Supreme Court (Ingersoll v. Palmer (43 Cal.3d 1321 (1987)) wherein the Court set forth what it felt to be necessary standards in planning and administering a sobriety checkpoint:
 * Decision making must be at a supervisory level, rather than by officers in the field.
 * A neutral formula must be used to select vehicles to be stopped, such as every vehicle or every third vehicle, rather than leaving it up the officer in the field.
 * Primary consideration must be given to public and officer safety.
 * The site should be selected by policy-making officials, based upon areas having a high incidence of drunk driving.
 * Limitations on when the checkpoint is to be conducted and for how long, bearing in mind both effectiveness and intrusiveness.
 * Warning lights and signs should be clearly visible.
 * Length of detention of motorists should be minimized.
 * Advance publicity is necessary to reduce the intrusiveness of the checkpoint and increase its deterrent effect.

Effectiveness
There is a dearth of research regarding the deterrent effect of checkpoints. The only formally documented research regarding deterrence is a survey of Maryland's "Checkpoint Strikeforce" program. The survey found no deterrent effect: "To date, there is no evidence to indicate that this campaign, which involves a number of sobriety checkpoints and media activities to promote these efforts, has had any impact on public perceptions, driver behaviors, or alcohol-related motor vehicle crashes and injuries. This conclusion is drawn after examining statistics for alcohol-related crashes, police citations for impaired driving, and public perceptions of alcohol-impaired driving risk."

Centers for Disease Control and Prevention, in a 2002 Traffic Injury Prevention report, found that in general, the number of alcohol-related crashes was reduced by 20% in states that implement sobriety checkpoints compared to those that do not.

Public Health Law Research, an independent organization, reported in a 2009 evidence brief summarizing the research assessing the effect of a specific law or policy on public health, that there is strong evidence supporting the effectiveness of selective breath testing sobriety checkpoints as a public health intervention aimed at reducing the harms associated with alcohol impaired driving.

The debate regarding saturation patrols versus checkpoints favors saturation patrols being more effective, both in terms of number of arrests and cost. The FBI compared saturation patrols vs. checkpoints in Ohio, Missouri, and Tennessee. The study showed that, “Overall, measured in arrests per hour, a dedicated saturation patrol is the most effective method of apprehending offenders.” Another survey found that "States with infrequent checkpoints claimed a lack of funding and police resources for not conducting more checkpoints, preferred saturation patrols over checkpoints because they were more 'productive,' and used large number of police officers at checkpoints."