It's like Snowpiercer without the weird drugs or cannibalism.
The word to remember here is “momentum.” Momentum is the product of mass and velocity, and simply put, it means that objects with a larger mass (like a train) will have a tremendous amount of force behind them, even at low speeds. This isn't always obvious while watching trains, but the following video is a pretty dramatic practical demonstration. It shows a CN train in Canada throwing up huge amounts of snow from the tracks as it goes.
As you can see, it isn't moving very fast, and it doesn't have a plow attached, it's just using its momentum to bash right through.