About Warning signs J: triangle, not a command: which statement is WRONG?
J10 = level crossing WITH barriers. Dangerous crossroads is J8.
J16 = roadworks. Level crossing with barriers is J10.
At sign J17 (road narrowing) you are legally required to a specific, fixed lower speed.
J-signs are warning signs, not order/prohibition signs; J8 only warns, it does not regulate priority — that follows from B-signs, shark's teeth, or the main rule.
Explanation
trap: a warning confused with a standardised maximum-speed sign. A warning sign imposes **no fixed speed**; you must adjust your speed yourself so that you can stop within the distance you can see