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CE 515 Railroad Engineering. Railway Track Design Source: AREMA Ch. 6 Stationing& Horizontal Alignments. “Transportation exists to conquer space and time -”. Railway Track Design. Key factors for rail alignment Operator has no control over horizontal movement
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CE 515 Railroad Engineering Railway Track Design Source: AREMA Ch. 6 Stationing& Horizontal Alignments “Transportation exists to conquer space and time -”
Railway Track Design Key factors for rail alignment • Operator has no control over horizontal movement • Less relative power available for locomotion relative to the mass to be moved • Long and thin physical dimension
Railway Track Design Considerations for designing rail alignments • Type of train traffic • Volume of traffic • Speed
Stationing Stationing • A single station: 100 feet long from beginning point to end point Milepost • Less precise, but more easily identified
Horizontal Alignments Two components: Tangents and Curves Tangents: established first • A straight line between two points • Denoted with bearings • Need a starting point and length to locate in space Curves: established based on tangents • Point of Intersection (PI) - fixed • Define the tangents • Points of curve defined subsequently
Horizontal Curves Important components of simple circular curve • Angle of Deflection (I) • Other aspects • see figure Source: AREMA
Degree of Curve Source: AREMA
Curves: Chord and Arc Definitions • Differences between two definition are slight at small degrees of curves • But increase as curves get sharper • North America freight railways use chord-defined • Highway design, some light rail system and other alignments design use arc-defined
Curves • Note: the radius of a four-degree curve is not exactly half of that of a two-degree curve Source: AREMA
Centrifugal Force • Can be counteracted by superelevation • Equilibrium elevation, allow more uniform speed Source: AREMA
Horizontal Alignments Under-balance • Difference between the equilibrium elevation and the actual superelevation • Limited tothree inches by FRA Source: AREMA pg.224
Spiral Curves • Transition from tangent level track to curved superelevatedtrack • Two functions • Gradual introduction of superelevation • Guiding the train from tangent track to curved track
Types of Spirals • Commonly used: the Searles, the Talbot, and the AREMA 10-chord spiral • Two Design Criteria • Rotational acceleration of the train about its longitudinal axis • Limiting value of twist along car body Recommended formula for the minimum length of spiral on AREMA pg. 225