Overhead lines, like most electrified systems, require a greater capital expenditure when building the system than an equivalent non-electric system. While a conventional rail line requires only the grade, ballast, ties and rails, an overhead system also requires a complex system of support structures, lines, insulators, power-control systems and power lines, all of which require maintenance. This makes non-electrical systems more attractive in the short term, although electrical systems can pay for themselves eventually. Also, the added construction and maintenance cost-per-mile makes overhead systems less attractive on long-distance railways, such as those found in North America, where the distances between cities are typically far greater than in Europe. Such long lines require enormous investment in overhead line equipment, and major difficulties confront energizing long portions of overhead wire on a permanent basis, especially in areas where energy demand already outstrips supply.