To help maintain alertness while driving, you should:

Taking short breaks before you're drowsy is an effective strategy for maintaining alertness while driving because it allows you to refresh your mind and body. Regular breaks can help prevent fatigue and reduce the risk of falling asleep at the wheel. Driving can be monotonous, and taking a moment to stretch, walk around, or simply rest your eyes can significantly enhance your focus and attention to the road.

In contrast, driving only during the day may help some drivers feel more alert, but it does not address the issue of drowsiness that can occur regardless of the time of day. Listening to loud music, while it may seem energizing, does not actually prevent fatigue and could even become a distraction. Eating high-protein snacks might provide a temporary boost in energy, but they can also lead to a crash in energy levels later on, especially if consumed in large quantities. Thus, actively managing your alertness through regular breaks is the most effective approach among the provided options.