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Raised pavement markings come in a variety of reflective colors, some of which (such as white and yellow) have guessable meanings derived from painted road symbols. But there are other colors, such as blue and green, that convey more information to those in the know.
Some colors will alert police, first responders or maintenance personnel, telling them where to find things like exits, fire hydrants or shut-off valves. Some options even have reversible colors that convey different messages depending on the direction of travel. But these values, like reflector designs, vary from place to place.
Cat’s eye was invented in 1933 by Percy Shaw in Boothtown, a suburb of Halifax, England. It features reflective glass beads inside a rubber and cast iron body. Each block is complex and dynamic, with different materials carefully designed to provide a variety of smart features.
The metal part of the case protects the device while emitting an audible alarm when a car passes, just like Botts Dots. At the same time, fixed rubber wipers clear the glass of dust by descending below the road surface. Cat Eye is also reflective, meaning it redirects light back to the source with minimal scattering, optimizing visibility of a moving vehicle. Today, some new versions of cat eyes are powered by solar energy, and the collected energy is then used to power LED lights (instead of the old reflective glass eyes).
Over time, different colors came to be used for different purposes. Usage is standardized throughout most of Europe:
Cat eyes are popular in the UK, probably in part because they work so well in fog, but they’re not the only solution in the world. Simpler trapezoidal designs can be found in many places. But the exact meaning of color coding varies from place to place, especially when it comes to less common colors and reversible variations.
About a decade after cat eyes appeared on the streets of Europe, other raised sidewalk markings began appearing in the United States. Many of the models still in use today are based on designs by engineer Sidney A. Heenan, who worked for the Stimsonite Corporation in Niles, Illinois. His marker, patented in 1967, was later improved by Ramon J. Asensio, who added a protective coating to improve impact and abrasion resistance. Over time, the brand has changed owners, but continues to operate.
Their raised reflective markings usually take the form of a pair of small ramps, one facing towards oncoming traffic and the other facing away from oncoming traffic. Although each is reflective and most have the same shape, different color schemes convey different messages to the driver. In North America:
In Australia the European convention prevails, although (as in the US) the color blue is used to indicate the presence of fire hydrants. The color yellow in Victoria has an additional function: a yellow dotted line with yellow reflectors indicates tram tracks on which other vehicles may travel. Meanwhile, solid lines and double yellow reflectors warn drivers not to cross the tracks.
Sidewalk markings have other uses, from art installations to country roads, hunting trails and private driveways. While Botts dots are being phased out in places like California, the future looks bright for other marking options.
It’s worth noting that in Canada, and I’m sure in the northern states, road reflectors are recessed and flush with the road surface to prevent them from being decapitated by snow plows.