Final answer:
Drivers carrying Division 4.3 materials must stop at railroad crossings regardless of the weight they are hauling.
Step-by-step explanation:
According to the Department of Transportation's Federal Motor Carrier Safety Administration (FMCSA), drivers carrying Division 4.3 materials, which are dangerous gases, must stop their vehicle at railroad crossings even if they are hauling below the threshold for Class 1 explosives or Class 3 flammable liquids. The weight of the Division 4.3 materials, such as oxygen, must not be a determining factor in whether or not to stop at a railroad crossing. So, in this case, you would need to stop your vehicle before a railroad crossing regardless of the weight you are hauling.