Which situation is illegal regarding turning left on red?

Turning left on red is a maneuver that is generally allowed under specific conditions. In most jurisdictions, it is legal to make a left turn on red when you are turning from a one-way street onto another one-way street, as this is typically seen as a safe and controlled maneuver. This option reflects the legal framework designed to facilitate traffic flow while ensuring driver and pedestrian safety.

On the other hand, making a left turn on red from a two-way street is often illegal because it poses significant safety risks. Two-way streets involve traffic coming from opposite directions, and turning left on red in such a scenario can lead to confusion and an increased likelihood of collisions. This is why turning left on red is restricted at two-way intersections—drivers must wait for the green signal to ensure that they have clear and unimpeded visibility of oncoming traffic.

The other scenarios provided involve specific traffic controls such as stop signs or lack of signage where the legality of turning on red can vary, but a left turn from a two-way street remains consistently prohibited in many locations.