Which of the following is a characteristic of drug testing under DOT regulations?

The characteristic of drug testing under DOT regulations that stands out is that tests must comply with specific federal guidelines. This compliance ensures that the testing process is standardized, reliable, and defensible. The regulations set forth by the Department of Transportation establish rigorous procedures and protocols, including how the collection, handling, and analysis of samples should be conducted. These guidelines also dictate who may perform the tests, how results are reported, and the consequences of testing outcomes.

Ensuring adherence to these federal guidelines is crucial for maintaining the integrity of the testing process and for protecting the rights of employees. This structured approach helps in preventing misuse or inaccuracies in the testing methodology and promotes fairness in the workplace.

Other options may not align with the comprehensive regulations set by DOT. For example, drug testing must be conducted under certain specified conditions rather than "at will," only urine samples are not used exclusively, and while privacy is important, testing can occur in various settings that meet the necessary standards rather than being limited to strictly private environments.