Mechanical friction at the wheel-rail interaction includes:

• Friction on both tangent and curved tracks due to rolling friction on the horizontal interface between wheel and rail.
• Curve resistance is the additional resistance in curves due to increased lateral friction forces in curves.

The sum of the two effects usually accounts for about 5 to 10% of a train’s energy consumption in passenger trains and up to 30% very heavy freight trains.

Rail and wheel lubrication aims at reducing lateral friction between rail and wheel. This is especially effective in curves but can also be applied on tangent tracks.

Rail lubrication is realised by special lubricating vehicles. Wheel lubrication can be achieved either by on-board or by stationary lubricators.