In this situation, when entering the tunnel, are you obliged to keep a distance of at least 100 meters from the preceding vehicle?

In the video you are approaching the entrance to a tunnel in town, marked with signs D-37 "tunnel"; the traffic lights above the roadway show a green signal, and the roadway has several lanes. You do not have to keep a distance of at least 100 m from the vehicle in front. The answer is: no.

The Road Traffic Act sets a minimum distance in tunnels only outside built-up areas and only in tunnels longer than 500 m: 50 m for a vehicle with a maximum permissible mass of up to 3.5 t or a bus, and 80 m for a vehicle combination and other vehicles; the traffic management authority may reduce or increase these distances with signs. So the figure of 100 m does not appear in the rule at all: in a tunnel in town no fixed distance in metres applies, and even in a tunnel longer than 500 m outside a built-up area it would be 50 m for a passenger car. However, the general rule always applies: you keep the distance needed to avoid a collision if the vehicle in front of you brakes or stops. The Regulation on road signs and signals states that sign D-37 marks the entrance to a tunnel; before it, you make sure that your dipped headlights are on.

Legal basis: Art. 19 para. 2 point 3 and para. 4-5 of the Road Traffic Act (Prawo o ruchu drogowym); § 56 para. 1 of the Regulation on road signs and signals