Bollards are short, vertical posts that are embedded in, or placed on, the pavement in order to define an area and often to prevent automobiles and other large vehicles from entering it.
Bollards exist in a wide variety of shapes and heights, and are commonly made from metal (steel, cast iron and aluminum), concrete, stone or plastic. Fixed bollards are typically the strongest and are often designed to withstand a severe hit from a vehicle. Removable bollards allow for quick installation and removal. Retractable bollards have electrically powered mechanisms that allow them to be raised or lowered into the pavement according to the situation or the time of day. Decorative bollards are intended to visually define an area or guide traffic and have little ability to physically block vehicles.