Which of the following indicates a well-maintained passenger transport vehicle?

A clean and functional interior is a strong indicator of a well-maintained passenger transport vehicle. It demonstrates that the vehicle has been cared for in a way that prioritizes passenger comfort and hygiene, which is essential in passenger transport. A tidy interior not only creates a pleasant travel environment but also suggests that the vehicle undergoes regular cleaning and maintenance checks, ensuring that all parts, such as seats, seat belts, and safety equipment, are in good working order.

Other options such as a regularly washed exterior and bright exterior paint may reflect some level of care, but they do not necessarily speak to the overall functionality and safety of the vehicle's interior environment. In contrast, outdated safety features would indicate potential negligence in maintenance and updates necessary to keep passengers safe, which clearly detracts from the notion of a well-maintained vehicle. Thus, the focus on a clean and functional interior best signifies thorough maintenance practices.