A cat's eye (also known as a Botts' dot or a raised pavement marker) is a device used in some countries for road construction. A safety device, it consists of one or more small retroreflectors built into a sturdy housing, capable of surviving as vehicles pass over it. In places where roads are subject to snow, they must also survive being driven over by a snow plough. They are placed along road markings, as they serve to highlight these markings at night. They are particularly useful when lighting is poor, and can be used in addition to or as a replacement for other types of reflective road markings.

Cat's eyes were invented in 1933 by Percy Shaw of Yorkshire in England. The name "cat's eye" comes because the inventor was inspired when he saw light reflecting from cat's eyes. They became popular in Britain during World War II, in the era of blackouts. The Government realised that drivers needed to see where they were going, even in the midst of a blackout. Cat's eyes use a system where the light is reflected from the car's headlights, thus allowing a limited amount of light. There are now some self-illuminated versions, either wired to a power supply or using solar power. These increase visibility range. An unexpected benefit of cat's eyes is the typical thunk sound made when driving over the device, warning a driver that they have started to leave their lane.

In the UK, cats eyes retract into a housing when driven over - the lenses are cleaned against a rubber scraper as they move, thus ensuring they are visible.

Contents

1 Local practice 1.1 United Kingdom 1.2 United States 2 External links

Local practice

United Kingdom

Various types of cat's eye exist. In Britain, white cat's eyes are used for the centre of a road, lane markings, or soft traffic islands . Red cat's eyes are placed along the hard shoulder of a motorway, and orange cat's eyes are placed along the edge of the central reservation. Green cat's eyes denote joining or leaving slip roads at junctions, and blue cat's eyes are used for police slip roads. In Ireland, usage is similar, but yellow cat's eyes are used on all hard shoulders, including motorways (red cat's eyes are not used, nor are blue). In addition, standalone retroreflector batons are often used on the verge of Irish roads.

United States

In many regions of the United States, similar objects called Botts' dots are used to mark lanes. They are named after Dr. Elbert Botts , a California Department of Transportation (Caltrans) engineer credited with inventing the epoxy used to attach the markers to the road. They come in two varieties: rounded white markers used for lane dividers; and square, colored, reflective markers used for other situations. Of the square markers, white markers are used (between clusters of the round markers) to indicate lane lines (often with red "wrong way" reflectors on the back side), yellow markers to separate traffic directions, and blue to locate fire hydrants.

The markers were developed in the 1950s and 1960s as a replacement for painted lane lines for several reasons, mainly due to painted lines becoming invisible during rain and because painting the lines exposed Caltrans workers to dangerous traffic situations. Early experiments, however, were disastrously unsuccessful until Botts' invention of a new epoxy; the glues available at the time were simply not strong enough, and both screws and nails had a bad habit of coming out of the pavement and puncturing tires.

Over the years, Caltrans has wavered back and forth between using asphalt and concrete for new freeways. The current trend is to use concrete, but since white Botts dots are hard to see on white concrete through sun glare, Caltrans has often been forced by public demand to paint lane stripes on freeways that run east-west (and thus face the sunrise or sunset).

Also, Botts dots are rarely used on freeways in regions where it snows because snow plows scrape them off. On such freeways in California, Caltrans solved this problem by using lane stripes in place of the round markers, and by carving little "dips" in between the stripes for the square markers so that the snow plows go straight over them. The small dips also provide an even larger "bump" than Botts dots alone.

As seen in the photograph to the right, some wealthy American cities are able to replace lane stripes with Botts dots altogether, so that paint is used only for turn arrows and crosswalks at intersections.

External links

• Astucia, cat's eye supplier
• Caltrans Botts' Dots fact sheet