The third brake light, as it is commonly called, is a brake light that sits high above a vehicle's taillights. Designed to sit in the line of sight of drivers following a vehicle, the third brake light is intended to serve as a warning that a vehicle is slowing down. An increase in rear-end collisions worldwide was attributed to drivers following vehicles too closely in congested traffic areas, which prevented drivers from easily seeing the tail and braking lights of vehicles ahead of them. By placing the third brake light high in the rear of a vehicle, it was thought that drivers following too closely to see the tail lights could at least see this raised brake light. Subsequent testing reveals that the third brake light may be responsible for a reduction in rear-end collisions.

Often mounted in the trunk lid or rear window of an automobile, a third brake light is designed to easily be seen over the hood line of a following vehicle. Many automobile designers use light-emitting diode (LED) units to blend more subtly into the vehicle's body lines. Some early versions of the third brake light used full-sized brake lights molded high into the rear body sides of the vehicle. Mini-vans and sport compact utility vehicles (SUVs) are the most common users of this type of taillight configuration. In order to maintain a clean air flow line over the vehicle, many sports cars have the third brake light molded into the trailing edge of a rear air spoiler.

The success of the third brake light in preventing rear-end collisions proved to work so well that motorcycle manufacturers have adopted the inclusion of the warning device into their designs. Many touring-type motorcycles that have large, rear-mounted luggage bags have a brake light mounted in the top of the bag. This allows the light to be seen clearly by most drivers regardless of the following distance of the trailing vehicle. Some motorcycle manufacturers have included a bright strobe light in this area of the luggage bag as well. The bright blinking light serves to get the attention of motorists approaching the motorcycle from the rear on busy highways.

One public testament to the third brake light is the emerging inclusion of the light in the world's most expensive custom-built hot rods and custom vehicles. In an effort to protect their investment, some owners of prized custom show vehicles are installing the lights in their cars. Often made from billet aluminum and LED units, these additions are gaining popularity in the show car circuit.