Effects
of Wide Gauge on Derailment Potential (Part
2 of 2) By Gary P. Wolf • January
1, 2005
Part 1 of "Effects
of Wide Gauge on Derailment Potential" examined
how wide gauge occurs, some of the symptoms and reasons why wide
gauge is undesirable. Part 2 of this article explores
how to correctly measure gauge and properly identify wide gauge
as the
cause of a derailment.After a derailment, track gauge should be
measured both before and after the point of derailment (POD).
Most railroads specify
that gauge should be measured for 15 stations (spaced 15.5 feet
apart) preceding the POD, and at least 5 stations beyond the
POD (if possible). The gauge is measured from a point 5/8 inches
below the top running surface of the rail. In addition to measuring
the static, or unloaded gauge, an attempt should be made to measure
the dynamic, or loaded, gauge. The FRA specifies in section 213.13
of the Track Safety Standards:
When unloaded track is measured
to determine compliance with this part, the amount of
rail movement, if any, that occurs while the track is
loaded must be added to the measurement of the unloaded
track.
In practical terms, the FRA is saying
that to correctly assess gauge conditions, any evidence of dynamic
gauge widening should
be added to the static, or unloaded, gauge. The telltale sign
of dynamic gauge widening is evidence on the tie surface that
the plate is moving laterally under load. This evidence is characterized
by shiny wood fibers burnished by the action of the tie plate
sliding laterally under each passing wheel. At the far extent
of the plate movement, upturned wood fibers will be evident (see
Figure 1). A gap between the base of the rail and the tie plate
shoulders indicates that the rail is likely moving laterally
against the shoulder of the tie plate.
The approximate total dynamic gauge is determined by adding the
amount of rail movement against the shoulder of the tie plate
and the amount of tie plate movement on the surface of the tie.
(Figure 2 indicates how these two areas of lateral movement are
added to the static gauge measurement to approximate total gauge "under
load.")
DECEMBER 2004 "Effects
of Wide Gauge on Derailment Potential (Part
1 of 2)" READ
ARTICLESEPTEMBER 2004 "Truck Warp:
Causes and Cures (Part 1 of 2)" READ
ARTICLEOCTOBER 2004 "Truck Warp: Causes
and Cures (Part 2 of 2)" READ
ARTICLEAUGUST 2004 "Effects of Rail Cant
on Wheel/Rail Forces and Derailment Potential" READ
ARTICLE
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In practical terms, the FRA is saying
that to correctly assess gauge conditions, any evidence of dynamic
gauge widening should
be added to the static, or unloaded, gauge. The telltale sign
of dynamic gauge widening is evidence on the tie surface that
the plate is moving laterally under load. This evidence is characterized
by shiny wood fibers burnished by the action of the tie plate
sliding laterally under each passing wheel. At the far extent
of the plate movement, upturned wood fibers will be evident (see
Figure 1). A gap between the base of the rail and the tie plate
shoulders indicates that the rail is likely moving laterally
against the shoulder of the tie plate.
The approximate total dynamic gauge is determined by adding the
amount of rail movement against the shoulder of the tie plate
and the amount of tie plate movement on the surface of the tie.
(Figure 2 indicates how these two areas of lateral movement are
added to the static gauge measurement to approximate total gauge "under
load.")
