Final answer:
A conductor trainee must have the current operating rulebook available at all times in accordance with the rule effective December 28, 2015, transitioning from the 2008 to 2015 standards.
Step-by-step explanation:
A conductor trainee must always have his/her current operating rulebook available as per the final rule signed on October 1, 2015, which became effective on December 28, 2015. This requirement ensures that all operational procedures and safety measures are being followed according to the most up-to-date standards. While the previous 2008 '03 standards may still apply in some regions, it is important to note that a transition to the current 2015 standards is expected, and the precise instructions for this shift will be outlined in the implementation rule for the current standards.