What occurs if the primary RCO presses the vigilance toggle for five seconds or longer?

When the primary Remote Control Operator (RCO) presses the vigilance toggle for five seconds or longer, the function associated with the vigilance system is engaged to ensure that the operator remains attentive while operating the equipment. In this particular case, pressing the toggle activates the sanders for 30 seconds, which helps to improve traction by applying sand to the tracks. This action is a safety feature designed to assist with preventing slipping and maintaining control over the locomotive's movement.

The other options describe outcomes that do not align with the function of the vigilance toggle. The locomotive stopping immediately or the alarm sounding are not the direct results of pressing the vigilance toggle but rather serve other operational safety measures. Releasing the brakes is also unrelated to the vigilance function, further clarifying that the activation of sanders is the intended response when the toggle is pressed for five seconds or longer.