openings for twistlock fasteners at each of the eight corners, to allow gripping the box from above, below, or the side, and they can be stacked up to ten units high.[39][nb 8] Regional intermodal containers, such as European and U.S. domestic units however, are mainly transported by road and rail, and can frequently only be stacked up to three laden units high.[39] Although the two ends are quite rigid, containers flex somewhat during transport.[43] Container capacity is often expressed in twenty-foot equivalent units (TEU, or sometimes teu). A twenty-foot equivalent unit is a measure of containerized cargo capacity equal to one standard 20-foot (6.1 m) long container. This is an approximate measure, wherein the height of the box is not considered. For example, the 9 ft 6 in (2.9 m) tall high-cube, as well as 4-foot-3-inch (1.3 m) half-height 20-foot (6.1 m) containers are equally counted as one TEU. Similarly, extra long 45 ft (13.72 m) containers are commonly designated as two TEU, no different than standard 40 feet (12.19 m) long units. Two TEU are equivalent to one forty-foot equivalent unit (FEU).[44][45] In 2014 the global container fleet grew to a volume of 36.6 million TEU, based on Drewry Shipping Consultants Container Census.[46][nb 9] Moreover, in 2014 for the first time in history 40-foot High cube containers accounted for the majority of boxes in service, measured in TEU.[46] Manufacturing prices for regular, dry freight containers are typically in the range of $1750—$2000 U.S. per CEU (container equivalent unit),[47] and about 90% of the worlds containers are made in China.[38] The average age of the global container fleet was a little over 5 years from end 1994 to end 2009, meaning containers remain in shipping use for well over 10 years.[6] Bottom structure features Forty foot or longer containers typically have a gooseneck tunnel, an indentation in the floor structure, that meshes with the gooseneck on dedicated container sem