The American National Standards Institute (ANSI) approved the American National Standard for High-Visibility Safety Apparel (ANSI/ISEA 107-2004).  This standard provides consistent, authoritative guidelines for the selection and use of high-visibility apparel in the United States.

ANSI/ISEA 107-2004 specifies three classes of garments based on work environment:

Class III
Class III garments provide the highest level of visibility to workers in high-risk environments that involve high task loads, a wide range of weather conditions and traffic exceeding 50 mph. Class III garments,  provide coverage to the arms and/or legs as well as the torso, and can include pants, jackets, coveralls or rain wear. The standard recommends these garments for all roadway construction personnel and vehicle operators, utility workers, survey crews, emergency responders, railway workers and accident site investigators.

Class II
Class II garments are for users who need greater visibility in poor weather conditions and whose activities occur near roadways where traffic speeds exceed 25 mph. This class of garment is suitable for railway workers, school crossing guards, parking and toll gate personnel, airport ground crews and law enforcement personnel directing traffic.

Class I
These garments are intended for workers who have ample separation from vehicular traffic that does not exceed 25 mph. Class I garments are often safety vests they are recommended for parking service attendants, workers in warehouses with equipment traffic, shopping cart retrievers, sidewalk maintenance workers and delivery vehicle drivers.