page_title: Slippery rail
section_title: Effects
hierarchical_section_title: Slippery rail / Effects
caption_attribution_description: Deutsch: Extreme Flachstelle mit Auftragungung, wie sie an der Jubiläumsveranstaltung der SBB in Erstfeld gezeigt wurde. Ursache der Flachstelle war eine nichtlösende Bremse (Bremsstörung). English: A flat spot on a rail vehicle wheel. The flat spot was caused by a standstill as a consequence of a brake failure. This specific wheel was on disposition at a SBB jubilee celebration in Erstfeld.
context_page_description: Slippery rail, or low railhead adhesion, is a condition of railways where contamination of the railhead causes trains to experience less adhesion. This can lead to wheelslip when the train is taking power, and wheelslide when the train is braking. The most common cause of contamination is fallen moist leaves that lie on and cling to the top surface of the rails of railway tracks. The condition results in significant reduction in friction between train wheels and rails, and in extreme cases can render the track temporarily unusable. In Britain, the situation is colloquially referred to as "leaves on the line".
context_section_description: The loss of friction between wheels and rail results in loss of tractive force — the wheels begin to spin, and in some instances the train is unable to move. In braking, substantial loss of friction results in reduced braking force. Braking distances are considerably longer, and in extreme cases the wheels may even lock up, causing the train to slide. Modern locomotives and multiple units are equipped with Wheel slide protection to counter slippery rail conditions.  Locked wheels can self-grind flat spots on the steel tyres, especially if the wheels are still sliding when arriving at a non-greasy section of rail, e.g. one that has previously been sanded.  This causes the wheels to go out of profile (known colloquially as 'wheel flats'), which subsequently leads to severe vibration and the need for the wheels to be re-profiled or re-tyred at great expense.
  In extreme cases, the build-up of leaf material can electrically insulate the wheels from the rails, resulting in a failure of signalling equipment to detect the presence of the train. Where the problem is severe, Track Circuit Actuators fitted to trains can help alleviate the problem.
  In the United Kingdom, it was estimated that the autumn leaves problem cost the rail industry GBP 60 million (USD 115 million) a year.
caption: Flat spot
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