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Traffic barriers (sometimes called crash barriers, or Armco barriers,〔AK Steel (formerly Armco) genericized trademark〕 also known in North America as guardrails or guard rails〔(【引用サイトリンク】url=http://www.oxforddictionaries.com/us/definition/american_english/guardrail )〕 and in Britain as crash barriers〔(【引用サイトリンク】url=http://www.oxforddictionaries.com/definition/english/crash-barrier )〕) keep vehicles within their roadway and prevent vehicles from colliding with dangerous obstacles such as boulders, buildings, walls or large storm drains. Traffic barriers are also installed at the road side to prevent errant vehicles from traversing steep (non-recoverable) slopes or entering deep water. Traffic barriers are installed within medians of divided highways to prevent errant vehicles from entering the opposing carriageway of traffic and help to reduce head-on collisions. Some of these barriers, designed to be struck from either side, are called median barriers. Crash barriers can also be used to protect vulnerable areas like school yards, pedestrian zones or fuel tanks from errant vehicles. While barriers are normally designed to minimize injury to vehicle occupants, injuries do occur in collisions with traffic barriers. They should only be installed where a collision with the barrier is likely to be less severe than a collision with the hazard behind it. Where possible, it is preferable to remove, relocate or modify a hazard, rather than shield it with a barrier. To make sure they are safe and effective, traffic barriers undergo extensive simulated and full scale crash testing before they are approved for general use. While crash testing cannot replicate every potential manner of impact, testing programs are designed to determine the performance limits of traffic barriers and provide an adequate level of protection to road users. ==Need and placement== Roadside hazards must be assessed for the danger they pose to traveling motorists based on size, shape and rigidity and distance from the edge of travelway. For instance, small roadside signs and some large signs (ground-mounted breakaway post) often do not merit roadside protection as the barrier itself may pose a greater threat to general health and well-being of the public than the obstacle it intends to protect. In many regions of the world, the concept of clear zone is taken into account when examining the distance of an obstacle or hazard from the edge of travelway. Clear zone, also known as clear recovery area or horizontal clearance is defined (through study) as a lateral distance in which a motorist on a recoverable slope may travel outside of the travelway and return their vehicle safely to the roadway. This distance is commonly determined as the 85th percentile in a study comparable to the method of determining speed limits on roadways through speed studies and varies based on the classification of a roadway. In order to provide for adequate safety in roadside conditions, hazardous elements such as fixed obstacles or steep slopes can be placed outside of the clear zone in order to reduce or eliminate the need for roadside protection. :Common sites for installation of traffic barrier: : *Bridge ends : *Near steep slopes from roadway limits : *At drainage crossings or culverts where steep or vertical drops are present : *Near large signs/illumination poles or other roadside elements which may pose hazards When barrier is needed, careful calculations are completed to determine length of need. The calculations take into account the speed and volume of traffic volume using the road, the distance from the edge of travelway to the hazard, and the distance or offset from the edge of travelway to the barrier. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Traffic barrier」の詳細全文を読む スポンサード リンク
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