What is indicated by the letter "D" on a driving license?

The designation indicated by the letter "D" on a driving license signifies that a prosthetic aid must be used while driving. This notation is important because it informs law enforcement and other drivers that the individual may have specific needs or accommodations, which ensures safety for both the driver and others on the road. The presence of a prosthetic aid indicates that the driver has been evaluated and approved to operate a vehicle safely with the necessary modifications or aids.

The other options do not accurately represent what the "D" signifies. For instance, restrictions related to passenger vehicles, hazardous materials transport, or manual transmission requirements are denoted by different letters or codes specific to those conditions. Understanding these codes helps clarify the capabilities and requirements for drivers regarding their specific driving situations.