Core: The real hierarchy: who overrules whom on priority?

Level 1, the highest: instructions from an officer or traffic controller. A hand signal from an authorised person overrides everything below it, including a red light — precisely because a light can malfunction or an emergency may call for different handling. Level 2: traffic lights, as long as they are working. When the light is active, it regulates priority above every sign — with one precise limit: the light overrides signs THAT REGULATE PRIORITY, not every other sign (a speed sign remains simply in force alongside a green light). Level 3: signs that regulate priority — signs such as B1, B2, B6, B7 and shark's-teeth markings. The book says so itself (p.46): traffic signs are used when the ordinary traffic rules are not sufficient. Level 4, the baseline: the traffic rules themselves, such as the rechts-regel. This applies only when nothing from levels 1 through 3 is present — which is exactly why an equal-rank junction (no marking at all) falls back to precisely this bottom level. A direct application of level 2: whoever enters on green does not have to give way to someone running a red light — the light determines priority, not the other driver's behaviour.