To ensure **safe driving**, it is essential to have good visibility around the vehicle. This includes keeping the windows clean and avoiding any obstructions that may hinder vision.

- **Sunshades**: These can be installed on the rear windows of a passenger car, but only under certain conditions. Specifically, the vehicle must be equipped with **two exterior rearview mirrors**, one on the left side and one on the right side. This ensures that, even if the visibility through the rear window is partially blocked by the sunshades, the driver can still see adequately through the side mirrors.

- **Rearview mirrors**: Passenger cars must have an exterior mirror on the left side and another on the right side, in addition to a central interior mirror. Although the right-side mirror is recommended, it is not mandatory, except when sunshades are installed on the rear windows.

Therefore, the installation of sunshades is permitted only if these specific visibility conditions are met through the rearview mirrors.