Term / expression
Description
Left/right rail
Planimetric position of the left/right rail of a
track.
The sense of the left/right rail is given by the
direction of increasing chainage.
When a section of the track is viewed in the
direction of increasing chainage, the left rail
is to the left of the centre of the track.
Nominal gauge
The nominal distance between the active
(internal) faces of the left and right rails.
Superelevation base
The distance over which the superelevation is
applied. This distance is normally the dis-
tance between the centre of the left and
right rail.
Left/right superelevation
Left/right cant
The superelevation or height difference of
each rail with respect to the track centreline.
Usually expressed in millimetres.
If one of the rails is used to rotate the track
section, or the height of the vertical align-
ment coincides with the lowest rail, the
superelevation of the rotation point or low-
est rail will be zero.
Superelevation is also known by the term
cant. These two words can be interchanged.
a
b
c
d
Rail_001
a
Track centreline
b
Left rail
c
Right rail
d
Nominal gauge
Two generic methods can be used to define the section of the track.
Method 1 - A definition using rotation around a known point
This method involves rotating the section around a known point, normally the
lowest rail.
e
a
b
f
d
c
Rail_002
a
Left rail
b
Right rail
c
Rotation point
d
Nominal gauge
e
Superelevation base
f
Superelevation (cant)
Diagram - Plan
Diagram - Section
Roads - General
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