When driving on main roads, which vehicles must use the hard shoulders where possible?

According to German traffic rules, slow-moving vehicles such as agricultural tractors and machinery (option 1) and mopeds (option 2) are required to use the hard shoulder when driving on main roads, if possible. This is because these vehicles travel at lower speeds and can obstruct faster traffic, so moving onto the hard shoulder helps maintain smooth and safe traffic flow. Small-engine motorcycles (option 3) are not specifically required to use the hard shoulder, as they can generally keep up with normal traffic speeds. Remember that using the hard shoulder in this context is meant to reduce speed differences and improve overall road safety.