is "covered" line wire. It is treated as bare cable, but often is safer for wildlife, as the insulation on the cables increases the likelihood of a large-wing-span raptor to survive a brush with the lines, and reduces the overall danger of the lines slightly. These types of lines are often seen in the eastern United States and in heavily wooded areas, where tree-line contact is likely. The only pitfall is cost, as insulated wire is often costlier than its bare counterpart. Many utility companies implement covered line wire as jumper material where the wires are often closer to each other on the pole, such as an underground riser/pothead, and on reclosers, cutouts and the like. Dampers Because power lines can suffer from aeroelastic flutter and "galloping" oscillations driven by wind, tuned mass dampers are often attached to the line, to change the characteristics of the line's physical oscillations. A common type is the Stockbridge damper. Compact transmission lines A compact overhead transmission line requires a smaller right of way than a standard overhead powerline. Conductors must not get too close to each other. This can be achieved either by short span lengths and insulating crossbars, or by separating the conductors in the span with insulators. The first type is easier to build as it does not require insulators in the span, which may be difficult to install and to maintain. Examples of compact lines are: Lutsk compact overhead powerline () Hilpertsau-Weisenbach compact overhead line () Compact transmission lines may be designed for voltage upgrade of existing lines to increase the power that can be transmitted on an existing right of way. Low voltage Low voltage overhead lines may use either bare conductors carried on glass or ceramic insulators or an aerial bundled cable system. The number of conductors may be anywhere between two (most likely a phase and neutral) up to as many as six (three phase conductors, separate neutral and earth plus street lighting supplied by a common switch); a common case is four (three phase and neutral, where the neutral might also serve as a protective earthing conductor). Train power Overhead lines or overhead wires are used to transmit electrical energy to trams, trolleybuses and trains. Overhead lines are designed on the principle of one or more overhead wires situated over rail tracks. Feeder stations at regular intervals along the overhead line supply power from the high-voltage