1. CE 515 Railroad Engineering
Railway Track Design
Source: AREMA Ch. 6
Stationing&
Horizontal Alignments
“Transportation exists to conquer space and time -”

2. 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

3. Railway Track Design Considerations for designing rail alignments
Type of train traffic
Volume of traffic
Speed

4. Stationing Stationing
A single station: 100 feet long from beginning point to end point
Milepost
Less precise, but more easily identified

5. 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

6. Horizontal Curves Important components of simple circular curve
Angle of Deflection (I)
Other aspects
see figure
Source: AREMA

7. Degree of Curve
Source: AREMA

8. 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

9. Curves
Note: the radius of a four-degree curve is not exactly half of that of a two-degree curve
Source: AREMA

10. Centrifugal Force Can be counteracted by superelevation
Equilibrium elevation, allow more uniform speed
Source: AREMA

11. Horizontal Alignments
Under-balance
Difference between the equilibrium elevation and the actual superelevation
Limited to three inches by FRA
Source: AREMA pg.224

12. Spiral Curves
Transition from tangent level track to curved superelevated track
Two functions
Gradual introduction of superelevation
Guiding the train from tangent track to curved track

13. 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

14. Questions?