page_title: Railway electrification system
section_title: Disadvantages
hierarchical_section_title: Railway electrification system / Comparisons / Electric versus diesel / Disadvantages
caption_attribution_description: English: The East Coast Main Line's Royal Border Bridge at Berwick-upon-Tweed.This is a photo of listed building number 1211052.
context_page_description: A railway electrification system supplies electric power to railway trains and trams without an on-board prime mover or local fuel supply.
  Electric railways use either electric locomotives, electric multiple units or both.
  Electricity is typically generated in large and relatively efficient generating stations, transmitted to the railway network and distributed to the trains. Some electric railways have their own dedicated generating stations and transmission lines, but most purchase power from an electric utility. The railway usually provides its own distribution lines, switches, and transformers.
  Power is supplied to moving trains with a continuous conductor running along the track that usually takes one of two forms: an overhead line, suspended from poles or towers along the track or from structure or tunnel ceilings, or a third rail mounted at track level and contacted by a sliding "pickup shoe". Both overhead wire and third-rail systems usually use the running rails as the return conductor, but some systems use a separate fourth rail for this purpose.
context_section_description: Electrification cost: electrification requires an entire new infrastructure to be built around the existing tracks at a significant cost. Costs are especially high when tunnels, bridges and other obstructions have to be altered for clearance. Another aspect that can raise the cost of electrification are the alterations or upgrades to railway signalling needed for new traffic characteristics, and to protect signalling circuitry and track circuits from interference by traction current. Electrification may require line closures while the new equipment is being installed.
  Appearance: the overhead line structures and cabling can have a significant landscape impact compared with a non-electrified or third rail electrified line that has only occasional signalling equipment above ground level.
  Fragility and vulnerability: overhead electrification systems can suffer severe disruption due to minor mechanical faults or the effects of high winds causing the pantograph of a moving train to become entangled with the catenary, ripping the wires from their supports. The damage is often not limited to the supply to one track, but extends to those for adjacent tracks as well, causing the entire route to be blocked for a considerable time. Third-rail systems can suffer disruption in cold weather due to ice forming on the conductor rail.
  Theft: the high scrap value of copper and the unguarded, remote installations make overhead cables an attractive target for scrap metal thieves. Attempts at theft of live 25 kV cables may end in the thief's death from electrocution. In the UK, cable theft is claimed to be one of the biggest sources of delay and disruption to train services — though this normally relates to signalling cable, which is equally problematic for diesel lines.
  Birds may perch on parts with different charges, and animals may also touch the electrification system. Dead animals attract foxes or other predators, bringing risk of collision with trains.
  In most of the world's railway networks, the height clearance of overhead electrical lines is not sufficient for a double-stack container car or other unusually tall loads. It is extremely costly to upgrade electrified lines to the correct clearances (21 ft 8 in or 6.60 m) to take double-stacked container trains.
caption: The Royal Border Bridge in England, a protected monument. Adding electric catenary to older structures may be an expensive cost of electrification projects
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