In this scenario, could the vehicle travelling by the roadside pose a hazard?

In the video you are driving in the right-hand lane of a dual carriageway outside town; a red car is overtaking you on the left, and ahead of you a light-coloured car is moving along the right shoulder. The vehicle moving along the shoulder may be a hazard. The answer is: yes.

The Road Traffic Act requires a driver to drive on the roadway, as close as possible to its right-hand edge, and a solid edge line prohibits cars from driving onto the shoulder - the shoulder is for pedestrians, bicycles and horse-drawn vehicles; the principle of limited trust tells you to be prepared for unusual behaviour by a road user when the circumstances suggest it. A car driving on the shoulder is exactly such a circumstance: it is going slower than the traffic on the roadway, it may come back into your lane at any moment to go around an obstacle on the shoulder, or it may suddenly stop. You also do not know why it is driving there - maybe it is looking for a place to stop, maybe it has broken down. You treat it like a vehicle which is about to join traffic: you slow down, and when the red car has passed you, you keep to the left part of your lane and watch the indicators and wheels of the car on the shoulder.

Legal basis: Art. 16 para. 4 and 5, Art. 11 para. 1, Art. 4 and Art. 3 para. 1 of the Road Traffic Act (Prawo o ruchu drogowym); § 86 para. 8 of the Regulation on road signs and signals