What distance from the preceding vehicle should you keep when driving a passenger car outside the built-up area in a tunnel 600 metres long?

According to Art. 19 para. 4 of the Road Traffic Act, in tunnels longer than 500 m (outside built-up areas), the driver of a passenger car is obliged to maintain a distance of at least 50 metres from the preceding vehicle. This regulation is intended to prevent pile-ups in a confined space.