Which of the following forms of ID is commonly used for domestic travel?

A driver's license is commonly used for domestic travel in the United States as it serves as a government-issued form of identification that meets the requirements set by the Transportation Security Administration (TSA) for air travel. It verifies the traveler’s identity, age, and lawful presence in the country. A driver's license is widely accepted at airport security checkpoints and is familiar to airline personnel, making it the preferred ID for air travel among adults.

In contrast, while a credit card can prove financial means, it does not establish identity sufficiently for security screening. An employee badge may not be recognized as valid identification outside of the workplace context, and library cards do not meet the identification requirements set for travel. Hence, a driver's license remains the standard identification for domestic air travel.