Fatigue Limit

A characters can travel for a limited number of hours before fatigue sets in, this is called their fatigue limit. A character's fatigue limit is equal to 8 + their Constitution modifier. This is the number of hours they can comfortably travel in a day. For each additional hour of travel beyond their fatigue limit, the character gains a level of exhaustion at the end of the hour.

A long rest resets the number of hours spent traveling to zero.