Gauge Face Angle is becoming an increasingly important measurement in the railway industry, particularly on rail transit systems. The shutdown of a transit system in the Eastern US after a derailment in which high gauge face angle was recorded has brought the measurement to the attention of transit systems across the country

What is Gauge Face Angle?

Gauge face angle (GFA) is an angle measured at the contact point of the wheel flange and the
gauge face of the rail, typically 5/8 inch below the top of rail. It is derived by fitting a straight line to
a restricted region of the gauge face of the rail. The region is bounded by two user-defined points,
one, typically about 2 mm above the gauge point and one about 2 mm below the gauge point. The
GFA is the angle in degrees that this line makes with a vertical line, defined by reference to
track level.

Why is GFA important?

Gauge-face angle has been identified as a causal factor in derailments and as a predictor of
wheel-climb derailment risk on rail transit systems. There have also been instances of low-speed wheel-climb derailments on Amtrak and commuter lines. The problem occurs when the wheel/rail contact angles flatten with wear, providing a shallower angle and easier path for wheel flanges to climb up the gauge face of the rail.

While the angle of the wheel flange and the gauge face of the rail are the primary causes of wheel-climb derailments, the coefficient of friction at the wheel flange / gauge face is also a contributing factor. An APTA Task Force, convened after a number of low-speed derailments occurred at Amtrak and commuter railroads, concluded that high levels of
friction, typically generated by wheel truing operations that left abrasive facets in the wheel flange, contributed to the likelihood of

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