When is a fuel cap not required on a vehicle?

A capless fuel system is designed to eliminate the need for a traditional fuel cap. In these systems, the fuel filler neck is designed in such a way that it has a built-in mechanism preventing fuel evaporation and maintaining the integrity of the fuel system without a removable cap. This leads to increased convenience for the driver and reduced risk of fuel spills.

Motorcycles typically require fuel caps for safety and functional reasons, while older vehicles may still have to comply with safety inspection regulations that include the necessity of caps. Electric vehicles do not use conventional fuel and instead usually rely on charging ports, which can also vary in design but generally do not involve removing a cap. Thus, the presence of a capless fuel system specifically identifies a situation where a fuel cap is not needed, making this the correct answer.