A cattle grid (or stock grid)(British English) or cattle guard (American English) – also known as a vehicle pass, Texas gate, stock gap (in U.S. Southeast[1] ) or, in New Zealand, a cattle stop – is a type of obstacle used to prevent livestock, such as sheep, cattle, pigs, horses, or mules from passing along a road or railway which penetrates the fencing surrounding an enclosed piece of land. It consists of a depression in the road covered by a transverse grid of bars or tubes, normally made of metal and firmly fixed to the ground on either side of the depression, such that the gaps between them are wide enough for animals' legs to pass through, but sufficiently narrow not to impede a wheeled vehicle or plantigrade foot. They rely for their effect (of barring passage to animals but not to wheeled vehicles) upon animals' reluctance to set foot upon them.
Cattle grids are usually installed on roads where they cross a fenceline, often at a boundary between public and private lands. They are an alternative to the erection of gates that would need to be opened and closed every time a vehicle passed, and are common where roads cross open moorland, rangeland or common land maintained by grazing, but where segregation of fields is impractical. Cattle grids are also used when otherwise unfenced railways cross a fenceline. Cattle grids are seen throughout the world and quite common in places such as Australia, the Scottish Highlands, or the National Parks of England and Wales. They are also common throughout the Western United States and Canada, where they are usually called a cattle guard or, occasionally, a Texas gate. In the USA, they are most often used on BLM and Forest Service land, but are also used on paved roads and even exit ramps of the Interstate Highway System in many rural areas.
While these barriers are usually effective, they can fail due to ingenious animals. Sheep have been known to jump or run along the side of grids as wide as 8 feet (2.4 m), traversing them to find more and better food or water. Wider grids are used where deer are to be contained. Some animals, particularly wildlife, can jump across them, and animals with particularly large feet, such as American bison or even particularly large bovine bulls, can walk across them without slipping between the bars. Sometimes, they may be connected to an electric fence to prevent predatory animals, such as dingoes and foxes walking over them. In areas with heavy snowfall and long periods without a thaw, snow can pile up under a grid and allow animals to walk across it.
Portable "Texas gates" suspend the gate by springs so that it lowers to the ground when a vehicle passes over then returns to a position 6 inches (15 cm) above the ground.
Painted lines on the road can serve as skeuomorphs of cattle grids. The light-dark pattern of lines and pavement resembles a true cattle guard to animals. Many animals see a more intense contrast between light and dark because their night vision is much better than humans'. Animals see the sharp contrast of the cattle guard on the ground as a false visual cliff; they act as if the dark parts are deeper than the light parts. Using a virtual cattle guard is cheaper than a true cattle guard, and can be used on higher-speed roads due to its smooth surface.[2]
"Electric cattle guards" use electricity to deter animals from crossing the fence line. The cattle guard is composed of a bi-layer rubber polymer that lays directly on ground. The lower layer insulates electricity from ground and the upper layer carries an electric charge which shocks any animal that touches the cattle guard and ground at the same time. The rubber polymer allows wheeled traffic to cross.
The United States Patent and Trademark Office (US PTO) issued patent # 1,125,095 dated 15 January 1915 to William J. Hickey, Reno, Nevada.[3]
There is a British Standard for cattle grids: BS4008:2006. The US standards are put forth by The American Association of State Highway and Transportation Officials (AASHTO). AASHTO provides load rating guidelines for cattle guards that are used on public roads in America. All cattle guards used on American public roads must be certified by a qualified engineer that the guard meets AASHTO guidelines.[4]