A cattle grid (or stock grid)(British English) or cattle guard (American English) – also known as a vehicle pass, Texas gate, stock gap (in the U.S. Southeast ) 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 fall through, but sufficiently narrow not to impede a wheeled vehicle or human foot. This provides an effective barrier to animals without impeding wheeled vehicles, as the animals are reluctant to walk on the grates.
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 when 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 US, they are often used on BLM and Forest Service land, but are also used on paved roads and exit ramps of the Interstate Highway System in rural areas.
While these barriers are usually effective, they can fail due to ingenious animals. Sheep searching for food have been known to roll over grids, jump across them, step carefully into the spaces or run along the side of grids as wide as 8 feet (2.4 m). 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 accumulate beneath a grid and allow animals to walk across. 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 to avoid the snowfall problem.
Concrete cattle guards
Pre-cast concrete cattle guards provide the benefit of superior strength since each beam is reinforced with steel rods. They also offer better resistance to the elements than steel. However, due to the sheer weight of concrete these cattle guards can be expensive to transport and offload.
Cattle guard forms
A cattle guard form is a cast in place, light weight, mold made of high density polyethylene. The form is pre-installed with reinforcing rods. Once the form is placed in or above ground it is then filled with concrete. The concrete form is constructed so concrete can flow and fill each beam. Once filled both form and concrete remain in place to cure. A finished cattle guard form poured with 4,000-pound-per-square-inch (28 MPa) concrete reinforced with 5⁄8-inch (16 mm) fiberglass (GFRP) rebar is engineer certified at an HS-20 load rating or 32,000 pounds (15 t) per axle.
Steel cattle guards
Steel cattle guards are constructed of 3-to-5-inch (76 to 127 mm) steel piping supported by 8-to-12-inch (200 to 300 mm) channel beams. Steel cattle guards are also expensive to transport and offload. Due to continued exposure to the elements steel cattle guards need to be painted or constructed from galvanized steel to minimize corrosion. In addition most steel cattle guards need to sit on a concrete footing or foundation for added stability.
Virtual cattle guards
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[dubious ] 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.
Electric cattle guards
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 lies 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.
Patents and standards
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 the US. All cattle guards used on American public roads must be certified by a qualified engineer that the guard meets AASHTO guidelines.
- Brown, Robert A (March 1960). "Fooling Cattle With Paint". Popular Science 176 (3): 228. Retrieved 2010-09-21.
- Sheep escaping on YouTube
- "Crafty sheep conquer cattle grids". BBC News. Retrieved 3 October 2014.
- Hendricks, Walt. "Cattle Guard Forms". Cattle Guards website. Ray Allen. Retrieved 20 November 2012.
- "Virtual cattle grids outsmart NT cattle - 28/07/2005". Australian Broadcasting Company. 28 July 2005. Retrieved 2010-06-17.
- "Patent Images-Cattle Grid". Retrieved 2011-02-16.
- "Information on Cattle Guards & Cattle Grates". Barn World Farm & Ranch Superstore. www.cattle-guards.com. Retrieved 2010-06-17.
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