Here in Australia, we are often asked by large roadside billboards to “drive to the conditions”. This means that your driving style should be adjusted depending on the time of day, weather, visibility, road conditions, and so on. And this is, of course, to prevent us from suffering road accidents.

While all that is obviously targeted at road users, you can easily imagine that something very similar will apply to railways, specifically to the driving of trains. Trains can have accidents too, for example, derailments due to overspeed in curves, over turnouts, or even on a straight line in extreme cases.

Not every train incident needs to be as serious as a derailment, but if you have ever heard about “slip-slide effects,” you know they can be quite serious too.

Wheel slip can occur when a train accelerates beyond the adhesion of the driving wheels (the wheels connected to the train’s propulsion) to the rail. The wheel then slips over the rail surface, causing a few extra wheel rotations without respective forward movement.

Why is this bad? It obviously increases the wear of both the slipping wheel and the rail head where such wheel slippage occurs. A bit of a mix of wheel lathing and rail grinding, but both undesired and inconsistent, potentially causing some “un-rounding” of wheels and “bumps” in the rail surface. It also involves determining the precise train location, which is based on counting wheel rotations from the last reference point. That is how it works in both ETCS and CBTC, which is why wheel slips are particularly undesirable when using those train control technologies.

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