designers were commissioned to design the system of signage: Jock Kinneir and his assistant (and later business partner) Margaret Calvert. The new signs were first used on the Preston bypass in 1958. Worboys Committee The UK government formed another committee in 1963 to review signage on all British roads. It was chaired by Sir Walter Worboys of Imperial Chemical Industries. The result was a document that defined traffic signing in Britain, the Traffic Signs Regulations and General Directions (TSRGD). It was first introduced on 1 January 1965 but has been updated many times since. It is comparable with the Manual on Uniform Traffic Control Devices in the United States. The TSRGD is a Statutory Instrument that prescribes the sign faces and permitted variants that may be used on UK roads. The TSRGD is supported by the Traffic Signs Manual (TSM), which consists of eight separately-published chapters which provide "the codes to be followed in the use, siting, and illumination of signs both on all-purpose roads and motorways. It also covers temporary signs for use in connection with road works, in an emergency by the police, and temporary route signing by motoring organisations and highway authorities." Guildford Rules To eliminate sign clutter in the mid-1980s, a colour-coding system was developed to indicate different route types on a single sign. The system, also adopted in the Republic of Ireland, became known as Guildford Rules, after trials in Guildford, Surrey. Design Detailed guidelines govern road signs in the United Kingdom. The basic units of measurement used by sign designers and typographers are the 'x-height' (the height of the lower case letter 'x') and the 'stroke width' (sw) (4 sw = 1 x-height). The sizes of borders, symbols and arrows and the spacing and layout of the sign face are expressed in sw, so that all the elements remain in proportion. The x-height of a sign is dictated mainly by the speed of traffic approaching it; hence x-heights are common on motorways, whereas parking signs are mostly at or x-height. Shape Almost all signs have rounded corners. This is partly for aesthetic reasons. It is also safer for anyone coming into contact with a sign, and it makes the sign more durable, as rain and snow are less likely to corrode the corners. Units of measurement The United Kingdom uses mostly imperial units on road signs for distance measurements and speed limits. Vehicle weight