Final answer:
According to U.S. Department of Transportation regulations, vehicles transporting Division 4.3 hazardous materials must stop at railroad crossings to ensure safety.
Step-by-step explanation:
Based on the United States Department of Transportation hazardous materials regulations, vehicles transporting certain types of hazardous materials must stop at railroad crossings, regardless of the weight of the shipment.
This is to ensure the safety of the driver and the surrounding environment, as materials classified as Division 4.3 (Dangerous when wet) could react dangerously if involved in an incident at a rail crossing. It's important for drivers to understand and comply with these regulations to prevent any potential accidents or hazardous releases.