When are dash-mounted emergency lights prohibited?

Dash-mounted emergency lights are prohibited primarily when they obstruct or impair the driver's view. The safety of the operator and other road users is paramount, and if the lights impede the driver's ability to see the road, other vehicles, or pedestrians, they present a significant hazard. For instance, lights that are too large or improperly positioned can create blind spots or distractions, compromising the driver's focus and reaction time.

The other options, while addressing specific scenarios involving emergency lights, do not encapsulate the overarching reason for prohibition. Red lights could indicate emergency use but aren't the sole factor in their restriction. Similarly, while non-emergency vehicles should not have these lights, that concern is less about safety in the moment of driving compared to visibility issues. Lastly, the motion of the vehicle can be a factor, but the critical issue remains that any obstruction to the driver's view is what directly influences safety on the road.