Which document do you have to carry with you for a bus in cross-border traffic within the EU states?

For cross-border bus travel within EU countries, it is required to carry a certified copy of the valid license specifically for commercial cross-border passenger traffic with coaches and buses. This serves as proof that the bus operator is authorized to transport passengers across EU borders. Items like timetables or location descriptions are not considered official documents for granting cross-border traffic rights. Always make sure to have this certified copy with you to comply with EU regulations and to avoid legal issues during international journeys.