page_title: North American railroad signals
section_title: Mounting
hierarchical_section_title: North American railroad signals / Common signaling practices / Mounting
caption_attribution_description: English: PRR signal bridge at MP 304 on the Buffalo Line lit up for an approaching train. Replacement mast signals are in place behind the gantry, but have been sitting there for years.
context_page_description: North American railroad signals generally fall into the category of multi-headed electrically lit units displaying speed-based or weak route signaling. Signals may be of the searchlight, color light, position light, or color position light types, each displaying a variety of aspects which inform the locomotive engineer of track conditions so that he or she may keep their train under control and able to stop short of any obstruction or dangerous condition.
  There is no national standard or system for railroad signaling in North America. Individual railroad corporations are free to devise their own signaling systems as long as they uphold some basic regulated safety requirements. Due to the wave of mergers that have occurred since the 1960s it is not uncommon to see a single railroad operating many different types of signaling inherited from predecessor railroads. This variety can range from simple differences of hardware to completely different rules and aspects. While there has been some recent standardization within railroads in terms of hardware and rules, diversity remains the norm.
context_section_description: Signals are most commonly mounted on trackside masts about 12 feet (3.7 m) to 15 feet (4.6 m) high to put them in the eyeline of the engineer. Signals can also be mounted on signal bridges or cantilever masts spanning multiple tracks. Signal bridges and masts typically provide at least 20 feet (6.1 m) of clearance over the top of the rail. Bracket masts are arranged with multiple signals are mounted on the same masts governing two adjacent tracks. Bracket masts tend to be the tallest type of signal to allow the train crew to see the signal over a train on the intervening track. Signals in electrified territory may be mounted on the catenary structure, and signals on bi-directional lines may be mounted back-to-back on the same mounting device.
  Prior to 1985, signals were required by regulation to be mounted above and to the right of the track they governed. This mounting was designed to allow the engineer to view the signal when driving a steam or diesel locomotive with a long nose that restricted the view to the left. In most situations, especially where bi-directional running was implemented, signals needed to be mounted above the track or on bracket masts to allow this right hand placement. As locomotive design changed to allow good visibility on both sides of the track, regulations were changed allowing railroads to shift to bi-directional mast type signals, using signal bridges only in special situations involving multiple tracks or restricted views.
  Dwarf signals are typically mounted on the ground in areas of low speed movements or restricted clearances. Dwarf signals may be sometimes mounted higher up on a small mast or other structure for improved visibility. These can be known as "high dwarfs" or "stick signals," but a tall mounting does not change the lower speed applications of the dwarf signal.
caption: A Pennsylvania Railroad position light signal bridge with replacement mast signals in the background. The design of steam locomotives meant that all signals had to be placed to the right of the running track. Current diesel engine design allows both left- and right-hand siting.
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