Which vehicles must stop at railroad crossings regardless of signals?

The choice indicating that church or school buses, common carriers, and hazardous material vehicles must stop at railroad crossings regardless of signals is correct because these vehicles are considered to be carrying potential hazards or vulnerable passengers.

Church or school buses often transport children, making it crucial for the driver to ensure their safety at all times, including at railroad crossings. Similarly, common carriers, which can include various types of vehicles transporting goods or passengers, are required to take extra precautions to protect the public. Hazardous material vehicles carry substances that could pose significant risks to public safety, so they are mandated to stop at railroad crossings to assess the situation before proceeding.

This requirement stems from the heightened risks associated with these vehicles. Stopping allows the drivers to ensure that no train is approaching, which is important for the safety of everyone on the road, especially when children or hazardous materials are involved.