Cat's eye (road)
The cat's eye is a retroreflective safety device used in road marking and was the first of a range of raised pavement markers. It originated in the UK in 1933 and is today used all over the world. It consists (in its original form) of two pairs of reflective glass spheres set into a white rubber dome, mounted in a cast iron housing. This is the kind that marks the centre of the road, with one pair of cat's eyes showing in each direction. A single-ended form has become widely used in other colours at road margins and as lane dividers. Cat's eyes are particularly valuable in fog and are largely resistant to damage from snow ploughs.
A key feature of the cat's eye is the flexible rubber dome which is occasionally deformed by the passage of traffic. A fixed rubber wiper cleans the surface of the reflectors as they sink below the surface of the road (the base tends to hold water after a shower of rain, making this process even more efficient). The rubber dome is protected from impact damage by metal 'kerbs' – which also give tactile and audible feedback for wandering drivers.
The inventor of cat's eyes was Percy Shaw of Boothtown, Halifax, West Yorkshire, England. When the tram-lines were removed in the nearby suburb of Ambler Thorn, he realised that he had been using the polished strips of steel to navigate. The name "cat's eye" comes from Shaw's inspiration for the device: the eyeshine reflecting from the eyes of a cat. In 1934, he patented his invention (patent No. 436,290 and 457,536), and on 15 March 1935, founded Reflecting Roadstuds Limited in Halifax to manufacture the items. The name Catseye is their trademark. The reflective lens had been invented six years earlier for use in advertising signs by Richard Hollins Murray, an accountant from Herefordshire and, as Shaw acknowledged, they had contributed to his idea.
Development and value 
The blackouts of World War II (1939–1945) and the shuttered car headlights then in use demonstrated the value of Shaw's invention and helped popularise their mass use in the UK. After the war, they received firm backing from a Ministry of Transport committee led by James Callaghan and Sir Arthur Young. Eventually, their use spread all over the world.
Local practice 
United Kingdom and Hong Kong 
- White cat's eyes are used for the centre of a road on many roads which lack street lighting but are subject to high speeds or high volumes of traffic. They are also used for lane markings, soft traffic islands and on "double-white lines" where no overtaking is permitted.
- Red cat's eyes are placed along the hard shoulder of motorways, dual carriageways, as well as the nearside (left) edge of major A- and B-class roads (often former trunk roads).
- Amber cat's eyes are placed along the edge of the central reservation (median).
- Green cat's eyes denote joining or leaving slip roads at junctions.
These units are not very visible in daylight and are generally used in conjunction with traditionally painted lines. Temporary cat's eyes with just a reflective strip are often used during motorway repair work. These are typically day glow green/yellow so they are easily visible in daylight as well as in darkness, they can then be used on their own for lane division.
Also seen during motorway repair work are plastic traffic pillars that are inserted into the socket of a retractable cat's eye rather than being free-standing. These are often used in conjunction with two rows of the temporary cat's eyes to divide traffic moving in opposite directions during motorway roadworks.
Solar powered cat's eyes known as solar road studs and showing a red or amber LED to traffic, have been introduced on roads regarded as particularly dangerous at locations throughout the world. However, shortly after one such installation in Essex in the autumn of 2006 the BBC reported that the devices, which flash almost imperceptibly at 100 times a second, could possibly set off epileptic fits and the Highways Agency had suspended the programme.
Flashing blue LED cat's eyes were demonstrated on the TV show Accident Black Spot, aired on Channel 4 on 19 December 2000, which alert the driver to potential ice on the road when a low enough temperature, provisionally set at 3°C (37°F), is reached. Proposed enhancements, for an "intelligent cat's eye" of the future, will see the standard white light change to amber for four seconds after the passing of a vehicle, or red if the following vehicle is too close or traffic ahead is stationary.
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, neither are blue). In addition, standalone retroreflector batons are often used on the verge of Irish roads. Green cat's eyes are used to alert motorists to upcoming junctions. There are limited installations of actively powered cats eyes, which flash white light, on particularly dangerous sections of road such as the single carriageway sections of the N11.
United States and New Zealand 
Botts' dots (research started 1953, compulsory in California from 1966) and other raised carriageway markers perform a similar function in areas of the United States and New Zealand that receive little snowfall. They seem to be less durable than cat's eyes, and frequently break free of the road surface when driven over, especially by freight vehicles, since they do not sink into the road. In areas of the U.S. receiving substantial accumulating snowfall which requires the use of snow removal equipment, recessed markers or those encased in protective metal (like cat's eyes) are frequently used.
In the morning of 25 April 1999 on the M3 motorway in Hampshire, England, a van dislodged the steel body of a cat's eye which flew through the windscreen of a following car and hit a passenger (the drum and bass DJ known as Kemistry) in the face, killing her instantly. The coroner recorded a verdict of accidental death. Investigators acknowledged that the cat's eye bodies occasionally came loose, but added that such an accident was previously unheard of. A question was asked in the House of Lords about the safety of cat's eyes in light of the incident, and the Highways Agency conducted an investigation into the "long-term integrity and performance" of various types of road stud.
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- "History". Reflecting Roadstuds Ltd. Archived from the original on 19 February 2009. Retrieved 24 April 2013.
- Reyburn, Ross (26 June 1999). The Birmingham Post. p. 50
- The History of British Roadsigns, Department for Transport, 2nd Edition, 1999
- British patent 289619 7 April 1927
- United States patent 1625905 26 April 1927
- "Case studies". Astucia Traffic Safety Systems. Retrieved 13 October 2009.
- "Cats eyes to improve safety on A65, North Yorkshire". Government News Network. 6 November 2006. Retrieved 15 March 2008.
- "New cat's eye 'could trigger fit'". BBC News (BBC). 2 January 2007. Retrieved 15 March 2008.
- Osborne, Alistair (1 April 2002). "Intelligent cat's eye gleams at bright market prospects ahead". The Daily Telegraph. Archived from the original on 11 September 2009. Retrieved 24 April 2013.
- "Pavement Markers". Virginia Department of Transportation. Retrieved 15 March 2008.
- "Kemistry". Fuller Up, the Dead Musician Directory. Retrieved 2 December 2008.
- "Cat's eye killed DJ". News of the World. 2 May 1999. p. 15. "David Lydford, of Hampshire Police, said: Cat's eyes sometimes work loose, but I have never come across an accident like this in my 28 years with the police."
- "13 December 1999". Parliamentary Debates (Hansard) (House of Lords). col. WA20. 13 December 1999