When should a train operator be particularly cautious about slipping the wheels on a yard track?

A train operator should be particularly cautious about slipping the wheels on a yard track at the beginning of a light rain due to the combination of moisture with dust and dirt accumulation on the rails. When it starts to rain lightly, this initial moisture can create a slippery film on the tracks, reducing friction between the train's wheels and the rail surface. This phenomenon can be especially problematic in yard operations where trains are moving at lower speeds and precision in control is crucial.

In contrast, during heavy rain, the water typically washes away much of the dirt and debris, though caution is still necessary. In dry conditions, the track might offer good traction. During winter snowfalls, while there is an immediate risk of slipping, operators often adjust their driving techniques, such as reducing speed and applying sand, to mitigate slipping risks effectively. Therefore, the initial rain situation poses a higher immediate risk of slipping due to the unanticipated slickness of the rail.