Traffic signs or road signs are signs erected at the side of or above roads to give instructions or provide information to road users. The earliest signs were simple wooden or stone milestones. Later, signs with directional arms were introduced, for example, the fingerposts in the United Kingdom and their wooden counterparts in Saxony.
With traffic volumes increasing since the 1930s, many countries have adopted pictorial signs or otherwise simplified and standardized their signs to overcome language barriers, and enhance traffic safety. Such pictorial signs use symbols (often silhouettes) in place of words and are usually based on international protocols. Such signs were first developed in Europe, and have been adopted by most countries to varying degrees.
Traffic signs can be grouped into several types. For example, Annexe 1 of the Vienna Convention on Road Signs and Signals (1968), which on 30 June 2004 had 52 signatory countries, defines eight categories of signs:
*A. Danger warning signs
*B. Priority signs
*C. Prohibitory or restrictive signs
*D. Mandatory signs
*E. Special regulation signs
*F. Information, facilities, or service signs
*G. Direction, position, or indication signs
*H. Additional panels
In the United States, Canada, Ireland, Australia, and New Zealand signs are categorized as follows:
*Street name signs
*Route marker signs
*Recreation and cultural interest signs
*Emergency management (civil defense) signs
*Temporary traffic control (construction or work zone) signs
*Railroad and light rail signs
In the United States, the categories, placement, and graphic standards for traffic signs and pavement markings are legally defined in the Federal Highway Administration's ''Manual on Uniform Traffic Control Devices'' as the standard.
A rather informal distinction among the directional signs is the one between advance directional signs, interchange directional signs, and reassurance signs. Advance directional signs appear at a certain distance from the interchange, giving information for each direction. A number of countries do not give information for the road ahead (so-called "pull-through" signs), and only for the directions left and right. Advance directional signs enable drivers to take precautions for the exit (e.g., switch lanes, double check whether this is the correct exit, slow down).
They often do not appear on lesser roads, but are normally posted on expressways and motorways, as drivers would be missing exits without them. While each nation has its own system, the first approach sign for a motorway exit is mostly placed at least 1000 m from the actual interchange. After that sign, one or two additional advance directional signs typically follow before the actual interchange itself.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』