What information is documented in a track geometry measurement system?

A track geometry measurement system documents a range of parameters that define the physical condition of the track, including gauge, alignment (both horizontal and vertical), crosslevel (or cant), warp, and track surface. Gauge is the distance between the two rails, measured at a specified distance below the rail head. Alignment refers to the horizontal and vertical position of the track relative to its designed location. Horizontal alignment measures deviations from a straight line or the designed curvature of curves. Vertical alignment measures deviations from the designed elevation profile, including dips, humps, and sags. Crosslevel, also known as cant or superelevation, is the difference in elevation between the two rails, which is designed to compensate for centrifugal force on curves. Warp is the rate of change of crosslevel over a short distance, which can indicate track twist or instability. Track surface refers to the overall smoothness of the rail running surface, which is measured as deviations from a smooth profile. In addition to these primary parameters, track geometry measurement systems also document location information, such as milepost or GPS coordinates, to precisely identify the location of each measurement. They also often record speed of the measurement vehicle, date, and time. The data collected by the track geometry measurement system is used to identify track defects, prioritize maintenance efforts, and monitor track degradation over time. For example, a track geometry car might record a section of track with excessive gauge widening and a sudden change in crosslevel. This information would be used to schedule maintenance to correct these defects and prevent a potential derailment.