2.1 Straight track
The most common periodic or quasi-periodic rail damage in straight track is a result of vehicle “hunting”. When this occurs, wheelsets and the vehicle oscillate from side-to-side in a very periodic manner. Where there is flange contact the rail appears almost identical to a high rail, with gauge face wear and RCF on the gauge corner. The opposite rail appears like a low rail, with a flattened profile. Half a cycle further along (5-15m typically), the rail that appeared like a high rail appears like a low rail, and vice versa.
There are several reasons that “hunting” appears in localised areas. The most common reasons are tight gauge and profiles that have worn to conform too closely to the wheels. These increase the “effective conicity” and reduce the vehicles’ “critical speed”. Trains hunted on the rails shown in Section 1.1 immediately after these were transposed because of the increase in conicity from running in the root of the wheel flange.
When a periodic pattern of such long wavelength becomes established in the rail, it is impossible to remove with current rail reprofiling techniques. Reprofiling can, however, be undertaken to reduce conicity, eliminate hunting and allow trains to run on the periodically worn rail.
Hunting is potentially a dangerous condition: apart from damaging rails, it can move the whole track laterally.