Legal Requirements of Roadblocks:
The Ingersoll/Palmer factors

The Supreme Court of California rendered a decision on the premiere California roadblock case, Ingersoll v. Palmer, in 1987. This decision set the standard for how law enforcement agencies must conduct roadblocks, otherwise known as sobriety checkpoints. The Supreme Court identified a number of factors for minimizing the intrusiveness on the individual while balancing the needs of society in keeping drunk drivers off the road:

1) Decisionmaking at the Supervisory Level:

Only supervisory law enforcement personnel, and not officers in the field, may make the decision to establish a sobriety checkpoint and select the site. This requirement is important to reduce the potential for arbitrary and random enforcement.

2) Limits on the Discretion of Field Officers:

A neutral mathematical formula, such as every driver, or every third, fifth, or tenth driver should be used in determining who to stop at the roadblock. This requirement takes away the discretion of the individual officer to stop any driver he/she chooses without any legitimate basis.

3) Maintenance of Safety Conditions:

Primary consideration must be given to maintaining safety for motorists and officers. In order to minimize the risk of danger to motorists and police, proper lighting, warning signs and signals and clearly identifiable official vehicles and personnel are necessary. The checkpoint should only be operated when the traffic volume allows the operation to be conducted safely.

4) Reasonable Location:

The location of roadblocks should be determined by policymaking officials rather than by officers in the field. The sites chosen should be those which will be most effective in actually stopping drunk drivers, such as roads which have a high incidence of alcohol-related accidents and arrests.

5) Time and Duration:

Law enforcement officials are expected to exercise good judgment in setting times and durations, with an eye to effectiveness of the operation, and with the safety of motorists in mind. With these considerations in effect, there are no hard and fast rules as to the timing or duration of the roadblock.

6) Indicia of Official Nature of Roadblock:

The roadblock should be established with high visibility, including warning lights, flashing lights, adequate lighting, police vehicles and the presence of uniformed officers. Not only are such factors important for safety reasons, but advance warning will reassure motorists that the stop is duly authorized, thus reducing fright or annoyance to the motorist.

7) Length and Nature of Detention:

Each motorist stopped should be detained only long enough for the officer to question the driver briefly and to look for signs of intoxication, such as alcohol on the breath, slurred speech, and glassy or bloodshot eyes. If the driver does not display signs of impairment, he or she should be permitted to drive on without further delay. If the officer does observe signs of impairment, the driver may be directed to a separate area for a roadside sobriety test. At that point, further investigation must be based on probable cause, and general principles of detention and arrest would apply.

8) Advance Publicity:

Advance publicity is important to the maintenance of a constitutionally permissible sobriety checkpoint. Publicity both reduces the intrusiveness of the stop and increases the deterrent effect of the roadblock. The thought is that advance notice limits intrusion upon the individual's personal dignity and security because those stopped would anticipate and understand what was happening. Further, advance publicity serves to establish the legitimacy of roadblocks in the minds of motorists.

The Supreme Court also stated that motorists who seek to avoid a roadblock may not be stopped and detained merely because they attempted to avoid the roadblock. However, if the motorist commits a vehicle code violation or displays obvious signs of intoxication, there is adequate probable cause to pull over the motorist, after which point general principles of detention and arrest apply.

If law enforcement does not follow the factors set out by the Supreme Court, the evidence gained as a result of the roadblock may be suppressed as an intrusion on the 4th Amendment rights of the motorist.