Why is it difficult to capture illegal U-turns?

[Nora]

Illegal U-turns may be difficult to capture when they occur in the absence of no U-turn signs or dedicated U-turn traffic signals. Scenarios where U-turns are prohibited: Intersections marked with no U-turn signs; if the road centerline is a solid line, whether it's a single yellow line or double yellow lines, U-turns are prohibited; no-left-turn intersections prohibit U-turns; U-turns are forbidden at pedestrian crossings along road sections. Precautions for U-turns: U-turns are prohibited at pedestrian crossings. Although pedestrian crossings in road sections with traffic separation barriers may not have no U-turn traffic signs, pedestrians have the right of way, and pedestrian crossings are treated as prohibitive signs. Any U-turn at a pedestrian crossing will be penalized as an illegal U-turn at a prohibited location.