Literally, on the side of the way or the road.

In railways, it means anything on or beside the tracks and thus includes the four foot, the six foot and the cess.

Trackside equipment is often referred to as wayside equipment.

Steel wheels on steel rails provide sufficient traction (grip) in normal circumstances. When the braking applied to driving axles exceeds the traction capacity, the wheels lose grip and begin to slide.

Wheel slide is more prevalent where the tracks are slippery (snow, dust, wet leaves, etc) or the braking axles are not universally connected and retard uniformly. 

Sand may be used to increase the traction between wheel and rail and some locomotives have detection systems to deal with wheel slide.

See also wheel spin. 

Steel wheels on steel rails provide sufficient traction (grip) in normal circumstances. When the torque applied to driving axles exceeds the traction capacity, the wheels lose grip and begin to spin. Wheel spin is more prevalent where the tracks are slippery (snow, dust, wet leaves, etc) or the driving axles are not universally connected and rotate uniformly (diesel hydraulic locomotives). 

Sand may be used to increase the traction between wheel and rail and some locomotives have detection systems to deal with wheel spin.

See also wheel slide. 

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Work method statements

This is defined a failure that does not conform to a "fail safe" state. As such, this kind of failure leads to an unsafe situation.

An easy example to understand this undesirable situation is a signal. Should the signal show a green aspect instead of the intended red aspect, the potential for an accident is high.

The opposite to wrong side failure is right side failure.