offset by lower installation cost. Design of aluminium lattice towers is similar to that for steel, but must take into account aluminium's lower Young's modulus. A lattice tower is usually assembled at the location where it is to be erected. This makes very tall towers possible, up to (and in special cases even higher, as in the Elbe crossing 1 and Elbe crossing 2). Assembly of lattice steel towers can be done using a crane. Lattice steel towers are generally made of angle-profiled steel beams (L-beam or T-beams). For very tall towers, trusses are often used. Wood Wood is a material which is limited in use in high-voltage transmission. Because of the limited height of available trees, the maximum height of wooden pylons is limited to approximately . Wood is rarely used for lattice framework. Instead, they are used to build multi-pole structures, such as H-frame and K-frame structures. The voltages they carry are also limited, such as in other regions, where wood structures only carry voltages up to approximately 30 kV. In countries such as Canada or the United States, wooden towers carry voltages up to 345 kV; these can be less costly than steel structures and take advantage of the surge voltage insulating properties of wood. , 345 kV lines on wood towers are still in use in the US and some are still being constructed on this technology. Wood can also be used for temporary structures while constructing a permanent replacement. Concrete Concrete pylons are used in Germany normally only for lines with operating voltages below 30 kV. In exceptional cases, concrete pylons are used also for 110 kV lines, as well as for the public grid or for the railway traction current grid. In Switzerland, concrete pylons with heights of up to 59.5 metres (world's tallest pylon of prefabricated concrete at Littau) are used for 380 kV overhead lines. Concrete poles are also used in Canada and the United States. Concrete pylons, which are not prefabricated, are also used for constructions taller than 60 metres. One example is a tall pylon of a 380 kV powerline near Reuter West Power Plant in Berlin. Such pylons look like industrial chimneys. In China some pylons for lines crossing rivers were built of concrete. The tallest of these pylons belong to the Yangtze Powerline crossing at Nanjing with a height of . Special designs Sometimes (in particular on steel