Glossary - S

Saw by A maneuver by which two trains can meet at a siding that's too short to hold either one of them. (If neither train fits, it's a double saw-by.) Scale The size of things on a model railroad relative to things on a real railroad. For example, in the most popular scale, HO, models are 1/87th full size. Schedule That portion of a timetable that lists the class, direction, number, and timings of regular trains. Scissors crossover Two crossovers interlaced with a crossing in the middle which allow trains to pass from one parallel track to the other in either direction. Scratchbuilding Making a model from raw materials and parts, not using kits. SD General Motors' designation for its six-axle "special duty" diesel locomotives. Sectional track Track in short, rigid pieces (fixed length and curve radii) that are easily joined to each other. Shay A type of geared steam locomotive used extensively in logging, mining, and industrial railroading. It had three cylinders mounted vertically on the right side of the boiler driving a crankshaft geared to all the axles. Short line A small railroad, generally Class II. See Class I railroad. Siding A side track with a turnout at each end. Passing sidings are long enough to let trains meet each other. Single slip switch A special condensed track component that combines the functions of two turnouts in a short distance. Allows only three possible routings, not the four of a double-slip. Slug A weighted locomotive unit with traction motors but no diesel engine or generator. Used in conjunction with a diesel locomotive for additional tractive force. Smokejack A chimney on a car or building. Snowshed A structure built over the track in mountainous areas to protect the tracks from snow and avalanches. SPDT Single-pole, double-throw. A type of electrical switch used in model railroading. See DPDT. Speed table In DCC, table of parameters specifying the motor voltage in response to a speed and direction command. Individual speed tables can be programmed for each locomotive, allowing locomotives from different manufacturers to work together in a consist. Spike On a prototype railroad, a forged steel fastener with an offset head that's driven into the ties to secure the rails. Spiral curve or easement A curve of gradually increasing radius that makes the transition between a tangent or straight track and a fixed-radius curve. Spot a car To place a car in its designated position, as at an industry or on a station track. Spring switch A turnout held in one position by a spring so that facing point traffic always takes the same route but trailing point traffic can run through the turnout from either track. Spur or spur track A dead end track, one with a turnout at only one end. Standard gauge In North America, the standard gauge between rails is 4' 8½". Stub switch A pointless turnout that changes its route by gently bending the approach or "fly" rails sideways (image). Styrene Short for polystyrene, a versatile plastic commonly used for modeling. Comes in sheets, blocks, and rods of many different thicknesses and sizes. Subroadbed The bottom or foundation layer of model track, usually made from plywood. Superelevation Raising the outside rail of curved track to help trains negotiate curves more easily and at higher speeds. SW General Motors' designation for its diesel switchers. Switch Electrical switches are usually called toggles. In a turnout, the "switch" is the assembly of moving points that select one route or the other. Switchback A track layout that requires a change of direction. Switch lock A padlock or an interlocking device that secures a switch so it cannot be moved. Switch machine A single- or double-coil electromagnetic mechanism for directing trains to one track or another at a turnout. A remote-control device that moves the switch points to select a route through a turnout. Switch motor A motorized point-moving machine. Switch rod A metal rod that connects switch points to each other and to a switch stand or switch machine. Switch stand Manual device that allows a turnout to be lined (changed) from one route to the other.

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