Raised pavement marker
A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, thermoplastic paint, glass or occasionally metal, and come in a variety of shapes and colors. Raised reflective markers, such as plastic, ceramic, or metal ones, include a lens or sheeting that enhances their visibility by retroreflecting automotive headlights, while glass road studs gather automotive headlights with a dome shape and reflect the lights with a reflective layer within. Some other names for specific types of raised pavement markers include convex vibration lines, Botts' dots, delineators, cat's eyes , road studs, or road turtles. Sometimes they are simply referred to as "reflectors". Convex vibration marking line. The surface of this type of vibrating coating line is distributed and scattered with raised bumps. Some bumps are coated with high-refractive-index glass beads. When a speeding vehicle runs over the raised road lines, it produces a strong warning vibration to remind the car driver of deviation from the lane. Perpendicular to driving directions, these marking lines are used for settled mainline toll plaza, ramp entrances, mountainous areas, continuous sharp turns, downhill sections and the end of the highway (intersection of  highway exit and the plane of the common roadway), gates and entrances of enterprises, institutions, and school. In the same direction of traffic driving direction, they are mainly settled in the median strip, edge lines, and dangerous sections of the road. Reflective raised pavement markers. In the United States, Canada, and Australia, these plastic devices commonly have two angled edges facing drivers and containing one or more corner reflector strips. The marker is generally held in place using butyl pads, epoxy glue, or bitumen. In areas with little snowfall, reflective raised pavement markers are applied directly on top of the  road surface. The device's retroreflective surface enables the device to be clearly visible at long distances at night and in rainy weather. The devices come in multiple colors which vary in usage depending on local traffic marking standards. In 1965 San Diego Police Motorcycle Officer Kenneth Grant Maine, improved upon, applied for a patent pending, and then submitted the white epoxy-resin reflective raised pavement markers to the California Bureau of Highways, the predecessor to the California Department of Transportation, now known as Caltrans. In areas where snowplowing is frequent, conventional markers are placed in a shallow groove cut  in the pavement, or specially designed markers are used which include a protective metal casting that is embedded in recesses in the pavement, allowing the marker to protrude slightly above the pavement surface for increased visibility, much like a cat's eye. Lit LED in-pavement Raised Pavement Markings (RPMs), help improve road safety, as they are more generally visible than reflective RPM markings as they are internally lit and don’t require headlights to show up. And, whilst the RPMs are usually raised, being so visible, in snowplow areas, these types of RPMs can be installed flush-mounted within  the pavement so that they completely avoid the snowplows. There are a number of types, ranging from a single LED point source RPMs, with limited daytime visibilities, (road studs), to multi-LED linear type RPMs, visible in all full sunlight and nighttime applications. Some lit RPMs can be visible and useful in both bright sunlight as well as nighttime applications, whilst others are only visible at nighttime or in low light applications. One of the key differences between these types is that lit linear RPMs, being linear, each lit unit provides both positional and directional guidance to viewers. For single -point source viewer directional guidance, a number of these units must all be viewed at the same time. In severe weather, such as fog or snow whiteouts, this may not be possible. Therefore, as each linear visual aid provides both positional and directional guidance, this type is more helpful as in a wider variety of weather conditions and light conditions. Some lit linear visual aids / RPMs, melt snow, without needing any additional heating elements, as such, these types or self-cleaning RPMs are more energy-efficient compared to those that need additional heating elements to melt snow so are NOT  self-cleaning. Linear visual aids are also more useful since they can be used for creating in-pavement signs and messages such as lit merge arrows. Whilst point source RPMs could be used for such signage, in practice, because they are installed so close together and much deeper within the pavement compared to linear RPMs, such usage would tend to damage the road, especially within the asphalt roads. Usage of color in Europe. In almost all European countries, such markers will include reflective lenses of some kind. Most appear white or gray during daylight; the colors discussed here are the  color of light they reflect. Because of their inconspicuousness during the day, they are always used in conjunction with painted retro-reflective lines; they are never seen on their own. The exception to the above rules are: Usage of color in North America. Colors can also be combined, with a different color facing each direction: The current trend for lane markings is to intersperse retroreflective paint lines with reflectors as seen on the majority of American highways. Usage of color in Australia. While Australian designs generally follow those in the US, the colors generally follow European usage. Differences from European  usage include: History. Cat's eyes made out of metal were the earliest form of retroreflective pavement markers, and are in use in the United Kingdom and other parts of the world. They were invented in the United Kingdom in 1933 by Percy Shaw and patented in 1934 (UK patents 436,290 and 457,536), and the United States in 1939 (US patent 2,146,359). On March 15, 1935, Shaw founded Reflecting Roadstuds Ltd, which became the first manufacturer of raised pavement markers. The plastic markers now used widely throughout the United States and elsewhere did not appear until more than two decades  later. They were originally invented by American engineer Sidney A. Heenan in the course of his employment with the Stimsonite Corporation in Niles, Illinois. Heenan filed an application for a patent on October 23, 1964. Patent No. 3,332,327 was subsequently granted on July 25, 1967. Stimsonite went on to become the leading manufacturer of retroreflective raised pavement markers in the United States and was acquired in 1999 by Avery Dennison Corporation. For six years, Avery sold Stimsonite's line under its Sun Country brand. In 2006, Avery sold its raised pavement marker division to Ennis Paint, one of the largest  manufacturers worldwide of paint for pavement markings (particularly lane markings). The company (based in Ennis, Texas) changed its name to Ennis Traffic Safety Solutions and now markets the Stimsonite product line and descendants under the Stimsonite brand. Other manufacturers of retroreflective raised pavement markers sold in the United States under various designs include 3M, Apex Universal, Vialume, and Ray-O-Lite. Glass road studs. Glass road studs have a very special shape: the upper half is a dome shape, and the lower half is a base covered with a reflective layer. They come in a variety of colors and  sizes to meet the requirements of different applications. Currently they are widely adopted in Taiwan and around the world. Cat's eyes. Cat's eyes, in their original form, consist of two pairs of retroreflective glass spheres set into a white rubber dome, mounted in a cast-iron housing. They generally come in a variety of colors. They have enjoyed widespread usage in the British Isles and elsewhere around the world. Botts' dots. Nonreflective raised pavement markers (also known as Botts' dots) are usually round, are white or yellow, and are frequently used on highways and interstates in lieu of  painted lines. They are glued to the road surface with epoxy and as such are not suitable in areas where snow plowing is conducted. They are usually made out of plastic or ceramic materials. Pedestrian crossing studs. In the UK, the area in which pedestrians should cross at pelican crossings is marked out by a series of markers. Usually, these are painted as squares on the road but occasionally a metal stud is used. These are usually square and made from unpainted steel or aluminum. Delineator. Delineators are tall pylons (similar to traffic cones or bollards) mounted on the road  surface, or along the edge of a road, and are used to channelize traffic. These are a form of raised pavement marker but unlike most such markers, delineators are not supposed to be hit except by out-of-control or drifting vehicles. Unlike their smaller cousins, delineators are tall enough to impact not only a vehicle's tires but the vehicle body itself. They usually contain one or more retroreflective strips. They can be round and open in the center or curved (45-degree sections) of plastic with a reflective strip. They are also used in low reflective markers in  a "T" shape. They can also be used to indicate lane closures as in cases where the number of lanes is reduced. The name "delineator" is also used for reflective devices attached to other objects which are technically not pavement markers.