Which of the following is prohibited for a person driving a commercial motor vehicle?

Driving while having a measurable amount of alcohol in their system is prohibited for a person operating a commercial motor vehicle due to strict regulations aimed at ensuring the safety of all road users. Commercial vehicle operators are held to a higher standard of responsibility because they are often in control of larger, more dangerous vehicles, and may be transporting hazardous materials or many passengers. The legal limit for blood alcohol concentration (BAC) for commercial drivers is significantly lower than that for non-commercial drivers, typically set at 0.04% or lower depending on jurisdiction. This measure is in place to reduce the risk of accidents and enhance public safety, as impairment can greatly diminish a driver's ability to control a vehicle, make sound judgments, and respond quickly to dangers on the road.

In contrast, driving without a passenger and driving in the rain do not inherently present safety risks compared to operating under the influence of alcohol. Moreover, taking an alternate route may be necessary for safety or efficiency, depending on circumstances such as traffic or road conditions. These options do not violate specific regulations governing commercial driving, making them permissible actions.