Duties of highway patrols or traffic police include the following:

• Traffic enforcement: enforcing laws and regulations intended to improve traffic safety, such as speed limits
• Emergency response: securing the scene of a traffic accident by using cones and flares as well as providing first aid to the injured
• Accident investigation: gathering evidence to determine the cause of a roadway accident
• Commercial vehicle enforcement: enforcing highway laws related to commercial transport, including weight limits and hazardous materials rules
• General law enforcement: assisting local police, especially in rural areas, and keeping an eye out for non-traffic violations
• Maintenance: observing and reporting damage to the roadways, and conducting hasty road surveys after disasters or the passage of inclement weather
• Education: providing public information, handouts and displays to encourage safe driving and usage of the roads

Germany

In Germany, traffic policing on highways is the responsibility of the Autobahnpolizei, otherwise of the state police.

United States

Many state police agencies in the United States are, for historical reasons, referred to as a highway patrol organization.

For instance, the California Highway Patrol is actually a state police agency, meaning that it is a police body having statewide authority to conduct law enforcement activities and criminal investigations. In addition to its highway patrol duties described above, it performs functions outside the normal purview of the city police or the county sheriff, such as enforcing traffic laws on state highways and interstate expressways, overseeing the security of the state capitol complex, protecting the governor, training new officers for local police forces too small to operate an academy, providing technological and scientific support services, and helping to coordinate multi-jurisdictional task force activity in serious or complicated cases. The California Highway Patrol also serves as bailiffs and courtroom deputies for certain state courts, such as the appellate courts. The state traffic enforcement agency retained the name "California Highway Patrol" after the merger of the smaller California State Police with the larger California Highway Patrol and the combination of their functions into one agency.

However, some Highway Patrol organizations, such as the North Carolina State Highway Patrol are specifically charged with the enforcement of traffic laws, and while able to enforce other laws, they are not "state police" agencies in the same vein as the California Highway Patrol or the New Jersey State Police. In other cases, states like Texas have a bona fide and appropriately-named state police department such as the Texas Department of Public Safety, of which only one arm is a highway patrol unit.