Which of these is used primarily as a form of identification for driving purposes?

A driver's license is primarily used as a form of identification for driving purposes because it serves as both proof of an individual's legal ability to operate a motor vehicle and a standard form of personal identification. It contains essential information such as the driver's name, address, date of birth, photo, and signature. This official document demonstrates that the individual has undergone the necessary testing and has met the state's requirements for driving a vehicle safely.

While other options may serve as identification in certain contexts, they do not specifically fulfill the legal requirements for driving. For instance, a passport card is typically used for travel or identification and is not a proof of driving competency. A Colorado digital ID is an identification option but is not universally recognized for driving like a driver's license. Similarly, a birth certificate is an important document for establishing identity, but it does not indicate that the person is authorized to drive. Thus, the driver's license stands out as the primary form of identification necessary for driving purposes.