What is prohibited when using motorways?

You answered correctly. On German motorways (Autobahnen), it is strictly forbidden to stop on the hard shoulder without emergency reason, to reverse, and to make U-turns. These actions are extremely dangerous and can cause serious accidents because traffic typically moves at high speed. Only use the hard shoulder in case of a breakdown or emergency. Reversing and U-turns are never allowed on motorways, not even to correct a missed exit. Obey these rules to ensure safety for yourself and others.