If you need to park the car on a road marked like this because it has broken down, are you obliged to place a warning triangle behind it within a distance of 100 m?

Yes, it is mandatory. The visible D-7 information sign (white car on a blue background) indicates the beginning of an expressway. According to Art. 50 para. 2 of the Road Traffic Act, in the event of a breakdown on an expressway or motorway, a warning triangle must be placed 100 m behind the vehicle. This distance is necessary due to high speeds and gives other drivers time to react.