What do trains proceed on while in Release mode?

In Release mode, trains operate based on the aspects provided by the Signal Train Detection System (STDS). This system is designed to ensure that the train can safely proceed through areas that have been cleared by signaling aspects. The STDS communicates relevant information about track conditions and signal status, allowing the engineer to make informed decisions.

Utilizing the STDS allows for a more controlled environment, where the train can be guided by signal indications that are specifically designed for safe operations. This contributes to overall system safety and efficient train movement. Operating under train signal aspects is essential for maintaining proper separation between trains and avoiding conflicts on the track.

The other options, such as automatic override signals, emergency signals only, and manual control signals, do not accurately describe the signal system in use during Release mode. These options represent different operational conditions or signal types that do not apply in a normal operating scenario where STDS is in effect. Thus, the correct answer emphasizes the reliance on STDS signal aspects for safe train operations in Release mode.