Rail Transport Operators are reminded that wheel loads effect safe guidance of vehicles on track. Excessive wheel loads can damage rolling stock components and track structures. Insufficient vertical wheel loads can result in wheel climb or rollover derailments.
Awareness of this is particularly important when operating Road Rail Vehicles (RRVs) because of the diversity of RRV designs, suppliers and applications. This safety message focusses on wheel loads on RRVs.
The load on the wheels must not exceed the limit/s set by the Rail Infrastructure Manager under any travelling or working condition. The limit is usually expressed as an allowable maximum axle load.
Good design, particularly of rail vehicles, aims to distribute vehicle weight across the wheels as evenly as possible in the static load condition. In other words, when the vehicle stands stationary on straight, flat track on horizontal ground, the load on the wheels should be as close to equal as possible.
Static wheel loads vary when the vehicle is standing on curved, twisted or sloping track1.
Wheel vertical loads vary further if the RRV is altering its load distribution during work activities by, for example, extending or swinging its boom or lifting or manipulating a weight.
Over and above these static loads vehicle-track dynamics arise when RRVs are in motion causing further variations of wheel loading. For example, the body mass of an RRV may displace and roll inwards in a curve with track cant when the RRV goes slowly through it (cant excess), or outwards in the same curve at higher speed (cant deficiency). In addition wheelsets, bolsters or any number of masses on a rail vehicle may resonate at certain speeds resulting in lateral (or other) instability causing high dynamic forces between wheel and rail.
As can be seen from the above description wheel loads on RRVs can be affected by design and manufacture, by track geometry, working conditions and vehicle running dynamics.
Rail vehicle designers, manufacturers and operators must adhere to standards in order to keep wheel loads within safe limits under all rail travelling and working conditions. These standards include: