Which of the following is NOT mandated by the national safety code?

The choice indicating that "Big vehicles" are not mandated by the national safety code highlights a crucial distinction regarding regulatory frameworks. The national safety code specifically targets defined categories of vehicles that pose significant safety considerations based on their operational parameters and potential risks.

In this context, "big vehicles" is an ambiguous term and does not fall under the specific regulatory categories outlined in the national safety code. Instead, the code focuses on tangible metrics like weight for commercial vehicles exceeding 5,000 kg and those with the capability to carry 10 or more passengers. These regulations ensure that vehicle safety standards and operational guidelines are met for vehicles that could impact public safety more directly. This specificity ensures that regulations are practical and enforceable.

On the other hand, vehicles under the Passenger Transportation Act are also clearly defined within the regulatory framework, emphasizing their operational standards as necessary to ensure safety for passengers. Consequently, identifying "big vehicles" as a non-mandated category reflects an understanding of how safety codes are structured around defined vehicle characteristics rather than vague descriptors.