Raised pavement marker
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A raised pavement marker is a safety device used on roads. These devices are usually made with plastic, ceramic, or occasionally metal, and come in a variety of shapes and colors. Raised reflective markers include a lens or sheeting that enhances their visibility by reflecting automotive headlights. Some other names for specific types of raised pavement markers include Botts' dots, delineators, cat's eyes, road studs, or road turtles. Sometimes they are simply referred to as reflectors.
Reflective raised pavement markers
In the United States, Canada, as well as Australia, these plastic devices commonly have two angled edges facing drivers and containing one or more corner reflector strips. 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. In areas with little snowfall, reflective raised pavement markers are applied directly to the road surface rather than being embedded into the surface. The device's reflective 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.
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.
- White markers — for lane markings. When used on dual-carriageways, motorways or one-way roads they may illuminate red on the reverse, to indicate drivers are traveling the wrong way.
- Yellow or amber markers — These are found next to the central reservation (U.S.: median) on motorways and dual carriageways and in the Republic of Ireland are also used on hard shoulders.
- Red markers — These are found by the hard shoulder on motorways and at the edge of the running surface on other roads. They are also occasionally used to indicate a no-entry road.
- Green markers — These are used where slip-roads (U.S.: off ramp) leave and join the main carriageway on dual carriageways. In some countries they are also used across the entrances of minor roads or accesses onto major single carriageway roads.
- Blue markers — Are used to indicate the entrance to police reserved slip-roads (these do not lead anywhere, they are to allow police to park and monitor motorway traffic).
The exception to the above rules are:
- Fluorescent yellow markers — These are used to indicate temporary lanes during roadworks on major roads  and are glued to the road surface, they are never embedded in it. Any painted markings will be removed from the road surface if they contradict the markers. They are fluorescent yellow in color, so they stand out in the day, but reflect white light at night. Where used they are much more numerous and dense than standards markers, as they are not used in conjunction with painted lines.
Usage of color in North America
- White markers — for lane markings or to mark the right pavement edge.
- Yellow or orange markers — These separate traffic moving in opposite directions, or mark the left pavement edge on one-way roadways.
- Blue markers — Usually used to mark the location of fire hydrants.
- Green markers — Usually used to indicate that emergency vehicles can open gates to enter a gated community.
Colors can also be combined, with a different color facing each direction:
- White and red or yellow and red — white or yellow for normal use in one direction, and red to indicate "do not enter" in the other direction
- White and black — white for marking lane restrictions (such as an HOV diamond) in one direction on a roadway that has "reversible" traffic flow, and black in the other direction when the markings don't apply
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 U.S., the colors generally follow European usage. Differences from European usage include:
- Blue — Usually used to mark the location of fire hydrants, as in North America
- Yellow — In addition to marking the median of freeways, in Victoria single yellow reflectors are used with broken yellow lines to denote tram tracks on which motorized traffic can drive, and double yellow reflectors are used with solid yellow lines to denote tram tracks on which motorized traffic may not drive other than to cross.
Cat's eyes were the earliest form of reflective 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 (U.S. patent 2,146,359). On March 15, 1935, Shaw founded Reflecting Roadstuds Ltd, which became the first manufacturer of raised pavement markers.
The designs now used widely throughout the United States didn't appear until more than a decade later. They are based on the invention of 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. Practical use of Heenan's invention was not realized until an abrasion and impact resistant coating was invented by engineer Ramon J. Ascencio of the Stimsonite Corporation, working with the original team. Ascencio et al., filed an application for patent April 20, 1977 which was subsequently granted under Patent No. 4,596,622 on June 24, 1986.
Stimsonite went on to become the leading manufacturer of raised pavement markers in the United States and was acquired in the mid-1990s by Avery Dennison Corporation. For about a decade, 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 reflective raised pavement markers sold in the United States under various designs include 3M, Apex Universal, and Ray-O-Lite.
Cat's eyes, in their original form, consist of two pairs of reflective glass spheres set into a white rubber dome, mounted in a cast iron housing. They are generally more durable than Botts' dots (they are snowplough safe) or other forms of markers and also come in a variety of colors. They have enjoyed widespread usage in the British Isles and elsewhere around the world.
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 an 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. Occasionally these are painted as squares on the road but more often a metal stud is used. These are usually square and made from unpainted steel or aluminum.
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 reflective 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.