The axle load of a rail is an important design consideration in the engineering of railways. It is basically the total weight bearing on the track. It is determined by the weight of rails, the density of sleepers and fixtures, train speeds, amount of ballast, and the strength of bridges and earthworks. Generally, a given side of the track is designed to bear the maximum axle load. If the track gets overloaded by heavily loaded trains, it can be damaged. Therefore, in order to achieve higher operating speeds, the axle load on the tracks needs to be balanced. An axle load measuring system prevents derailments by accurately measuring any imbalance in vehicle wheels.
This is done using strain gauges which are embedded into the axles. They are mainly immuned to environmental changes such as rain and cold temperature, which removes risk and uncertainty from the installation process. As the vertical and lateral forces exert stress/strain between the axle and the point of rail-wheel contact, the effect is maximum along the line joining the center of axle and rail-wheel contact point. So, strain gauges are fixed in the radial direction for measuring these forces.