Retroreflectivity, or retroreflection, is an optical phenomenon in which reflected rays of light are preferentially returned in directions close to the opposite of the direction from which the rays came.

Retroreflection is used for highway safety and measuring distance. The method used for measuring distance is called time-of-flight measurement, which can be used for great distances. In time-of-flight measurements, the distance from light source to target is determined by measuring the time it takes light to travel to the target and return to the sensor.

The most common and practical use of retroreflection technology is its application to highway safety. Pavement markings and road signs are two of the most important means of ensuring the safety of motorists during their travels. Retroreflectivity, or nighttime visibility of signs and pavement markings, is essential for efficient traffic flow, driving comfort, and highway safety in general. Pavement marking and road signs are visible at night because the light from headlights is reflected back into drivers’ eyes by retroreflectors embedded into the signs or road stripes.