Which of the following describes the "H" endorsement?

The "H" endorsement specifically pertains to the transport of hazardous materials. This endorsement is required for drivers who wish to haul substances deemed hazardous by federal regulations, which can include explosives, flammable materials, and toxic substances. The purpose of this endorsement is to ensure that drivers have been adequately trained in the safe handling, transportation, and emergency response procedures associated with these materials.

In contrast, the other options pertain to different endorsements: transporting passengers is covered under a separate endorsement, operating motorcycles requires a distinct motorcycle endorsement, and driving double trailers is also governed by its own endorsement. Each of these endorsements addresses specific vehicle operation qualifications and safety requirements, distinct from the specialized knowledge and training required for dealing with hazardous materials.