Traffic police

Traffic police (also known as traffic officers, traffic enforcement units, traffic cops, traffic monitors, or traffic enforcers) are units and agencies who enforce traffic laws and manage traffic. Traffic police help to assist in patrolling highways, directing traffic and address traffic infractions. They may be a separate agency from a main police agency, a unit or division within a police agency, or a type of assignment issued to officers; they can also be part of a transportation authority or highway authority.

It has been noted that:

...traffic police, who are regarded as peripheral to most police forces, participate in both authoritative intervention and symbolic justice. Perhaps alone of all the assignments, traffic police are full-service police. They are different from the rest, however, because their work is limited to a particular venue—namely, public thoroughfares—and to particular people—namely, those who operate motor vehicles. But in terms of work, traffic police are detectives as well as patrol officers.

Traffic police have existed in some form for nearly three centuries. Possibly the first traffic police force was established in London, England in 1722, when the Lord Mayor of London, in response to an increase in traffic during the 18th century, appointed three men to position themselves on London Bridge and ensure traffic kept to the left side of the road and did not stop in traffic, with the aim of ensuring traffic could continue to flow unabated.

One of the oldest and most basic forms of traffic policing is directing traffic. This is conducted by a traffic officer (usually only one) who stands in the middle of an intersection, using hand signals and occasionally also a whistle, a handheld traffic sign (usually a stop sign), or a handheld light stick to manage the flow of vehicles and pedestrians. The officer directing traffic is usually a foot patrol officer or an auxiliary officer, though officers with vehicles may also direct traffic, parking their vehicles out of the way. Officers directing traffic typically wear high-visibility clothing to provide visibility and avoid being struck by traffic, ranging from brightly colored uniforms (historically a white patrol cap or helmet with gloves) to neon-colored vests and coats with retroreflective strips.

Though common worldwide before traffic signs and traffic lights became commonplace, traffic direction is now rare in places where traffic lights are the primary mode of traffic management, where it is mostly limited to incidents where roadways are closed or obstructed, traffic is heavier than usual, or traffic lights are disabled or otherwise unavailable, such as during a power outage or at the scene of a traffic collision. Traffic direction continues to be a mainstay in places where traffic lights and signs are not used, or where traffic is so dense that directing traffic is more effective than relying on lights and signs alone.

One of the most common forms of traffic policing in the modern day is vehicular enforcement. This is conducted by police officers using vehicles, typically cars or motorcycles but occasionally also aircraft or watercraft, who directly enforce vehicular traffic. Vehicular enforcement is often very similar to regular police patrols, and may be a standard police responsibility in some agencies. Vehicular enforcement usually consists of the enforcement of speed limits, registration and licensing, driving under the influence, commercial vehicle inspection, and other vehicle-related laws and crimes. The most common methods of vehicular enforcement are traffic stops, checkpoints, and "watching traffic" along the shoulder of roadways using radar speed guns.

Some roads may be patrolled by aircraft, a declaration usually posted along such a roadway by the agency operating said aircraft. Though some motorists view this as mere deception used to promote slowing down, police aircraft actually do patrol some freeways, albeit rarely due to the costs in operating aircraft for lengthy periods. To measure a vehicle's speed, the pilots calculate the time it takes to travel between a set of road markings. Should the pilots determine the vehicle is speeding or violating a law, they follow it until a police unit in a land vehicle arrives to initiate a traffic stop.