Which of the following actions signifies a marked departure from reasonable driving conduct?

Driving significantly above the speed limit under risky conditions clearly signifies a marked departure from reasonable driving conduct due to the heightened danger it poses both to the driver and to others on the road. Speeding, especially in adverse conditions such as bad weather, low visibility, or heavy traffic, greatly increases the likelihood of losing control of the vehicle, reducing the driver's ability to respond effectively to sudden changes or hazards on the road.

This behavior not only exceeds established legal limits but also disregards the necessity for caution and consideration of road conditions, which are critical for safe driving. The combination of excessive speed and risky conditions exacerbates the risks of accidents, making it an egregious violation of safe driving principles.

In contrast, actions such as driving with a seatbelt, driving slightly over the speed limit, or changing lanes without signaling may indicate lapses in judgment or adherence to regulations but do not inherently carry the same level of danger or recklessness associated with significantly exceeding the speed limit in unsafe conditions.