Buses are allowed to carry less than 100 pounds of ___ in the passenger area.

The correct answer is that buses are permitted to carry less than 100 pounds of small arms ammunition (ORM-D) in the passenger area. This allowance exists because small arms ammunition is classified as "ORM-D" (Other Regulated Material – Domestic), which poses a relatively low risk when transported in small quantities.

When carried under the ORM-D classification, the requirements are less stringent than those for more hazardous materials, acknowledging that this type of material, when properly packaged, does not pose a significant danger to passengers or the public. Hence, the specific limit of 100 pounds enables operators to transport this type of ammunition efficiently while adhering to safety standards.

In contrast, substances like labeled radioactive materials, liquid Class 6 poisons, and explosive materials carry much higher risks and are subject to stricter regulations and prohibitions concerning their transportation in passenger areas. These categories involve greater potential hazards and, as a result, cannot be transported in the same manner, ensuring the safety of passengers and crew on the bus.