page_title: Railway slide fence
section_title: Consequences of slide fence activation
hierarchical_section_title: Railway slide fence / Consequences of slide fence activation
caption_attribution_description: English: Pennsylvania Railroad Pedestal type position light signal with red-stop lenses at CP-SOUTH FERRY near Duncannon . This signal governs southbound movements off of the controlled siding. The hand written SP board indicates to train crews that this signal is connected to a slide fence.
context_page_description: Part of a railway signaling system, a slide fence is a fence whose purpose is to prevent trains from being derailed by rock slides in mountainous areas where rock slides may occur without warning. The fence is designed to be displaced by a rock slide, causing the signaling system to display a stop aspect on nearby signals. As an alternative, a structural fence is designed to physically stop falling rocks from reaching the tracks.
context_section_description: When a train approaches a slide fence area, and the signal displays a stop aspect, the train is not permitted to proceed normally, because a rock slide has occurred. However, the rock slide may not prevent the safe passage of the train. For example, a large rock may have fallen off the cliff, broken through the slide fence, and continued to fall away from the track. After stopping, the train may obtain radio permission from the dispatch center to proceed slowly, watching for a dangerous rock slide. If the train is able to successfully pass through the slide area (that is, there is no danger), it may then be allowed to proceed normally.
  In North America slide fences are typically connected in such a way as to shunt the track circuit when activated. This causes signals on either side of the slide fence to display a restricting indication, requiring trains to travel at a speed enabling them to stop within one half the range of vision. On lines formerly operated by the Pennsylvania Railroad signals connected to a slide detector have an 'SP' placard, reminding engineers to watch for slides when governed by a restrictive speed signal.
  Once the slide fence has been activated (even if in error), all trains are affected until the slide fence is repaired by maintenance personnel. This may result in several hours of delay in train service.
caption: Hand-written slide protection placard on a PRR Pedestal type signal at CP-SOUTH FERRY indicates to engine crews that this signal is connected to a slide detector.
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