A Brief History of Road Signs: Traffic signs can be grouped into several types. For example, Annex 1 of the Vienna Convention on Road Signs and Signals (1968), with over 50 signatory countries, has eight categories of signs: • Danger warning signs • Priority signs • Prohibitory or restrictive signs • Mandatory signs • Special regulation signs • Information, facilities, or service signs • Direction, position, or indication signs • Additional panels In the United States and in Australia signs are categorized as follows: • Regulatory signs • Warning signs • Guide signs o Street signs o Route marker signs o Expressway signs o Freeway signs o Welcome Signs o Informational signs o Recreation and cultural interest signs • Emergency management (civil defense) signs • Temporary traffic control (construction or work zone) signs • School signs • Railroad and light rail signs • Bicycle 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. History
