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Raised pavement marker
From Wikipedia, the free encyclopedia
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 colours. Many varieties include a lens or sheeting that enhance their visibility by reflecting automotive headlights. Some other names for raised pavement markers include: Botts' dots, delineators, cat's eyes, road turtles[1], road studs, marbles, road cookies, drunk bumps, road braille, or simply reflectors.
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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 which is embedded in the pavement, allowing the marker to protrude slightly above the pavement surface for increased visibility, much like a Cat's eye [2]. 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. Some typical uses include:
- White markers — for lane markings. These sometimes have a reflective red lens on the opposite side to notify drivers of an incorrect direction of travel.
- Yellow or amber markers — In North America, these are found on the left, signifying the traffic direction change, or a median. They are also used on the right side to indicate the beginning of the shoulder.
- 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 — white for marking lane divisions 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.
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 the in 1934 (UK patents Nos. 436,290 and 457,536), and the United States in 1939 (US patent 2,146,359). On March 15, 1935, Mr. Shaw founded Reflecting Roadstuds Ltd which became the first manufacturer of raised pavement markers.[3]
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.
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). Ennis Paint (based in Ennis, Texas) 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[citation needed] or other forms of markers and also come in a variety of colours. They have enjoyed widespread usage in the British Isles and elsewhere around the world.
These are usually round, are white or yellow, and are frequently used on highways and interstates in lieu of painted lines. They are simply glued to the road surface and as such are not suitable in areas where snow plowing is conducted.
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 aluminium.[4]
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.
^ Cave, Kathryn. "State lab in fast lane of high-tech road gadgets." The Orange County Register, 21 October 1991, sec. A, p. 1.
^ Haldane, David. "Dots' Demise Denied." Los Angeles Times, 7 March 1997, sec. B, p. 1.
^ Martin, Hugo. "Behind the Wheel: The Botts Dot's Future May Hit a Bump in the Road." Los Angeles Times, 23 October 2001, sec. B, p. 2.
^ Richards, Gary. "It May Be End Of Road For Noisy Botts Dots." Contra Costa Times, 18 January 1997, sec. A, p. 3.
^ Rubenstein, Steve. "Caltrans Plots To Erase Lots Of Botts Dots." San Francisco Chronicle, 18 January 1997, sec. A, p. 13.
^ Stein, Mark A. "On the Button: The Quest to Perfect Botts' Dots Continues." Los Angeles Times, 11 August 1991, sec. A, p. 3.