For vehicles that are not specifically used for government officials but still carry a sense of formality or official use, two common terms that come to mind are:

Corporate car service: This term is often used for vehicles provided by a company for its executives or guests.
Executive shuttle: This refers to a service that provides transportation for business professionals, often between work sites or from airports to hotels.

Vehicles that are specifically used for government officials:
Government limousine: Often associated with high-ranking officials, this term emphasizes the luxury and official capacity of the vehicle.
Diplomatic car: Used for transporting diplomats and dignitaries, this term highlights the diplomatic context of the vehicle.