Before amud hashachar a person is allowed to travel, provided that he plans his departure in such a way that he will succeed in reciting Shacharit on time. However, after amud hashachar, a person is prohibited from going on his way; instead, he must pray first and only then may he leave. Even if he has to leave home so early that he will miss praying with the minyan in his area, whereas he will still be able to pray in a minyan at his destination, it is preferable for him to pray individually before departing (Mishnah Berurah 89:20).
This prohibition refers to setting out on a long trip, for that is the meaning of “yotzeh laderech” (going on one’s way). One interpretation maintains that the words refer to a journey that lasts at least 72 minutes (Shut Or L’Tzion, part 2, 7:6). In times of need one may rely on that opinion. Therefore, concerning a person who must start traveling earlier than the time of the minyan in his area, if his trip lasts less than 72 minutes, it is preferable for him to leave and then pray in a minyan at his destination. However, if his trip lasts longer than 72 minutes, it is best that he pray first in his area individually.
If the entire trip is for the sake of prayer, for example, traveling to recite Shacharit at the Kotel, one is permitted to depart before praying, even if the travel time will last more than 72 minutes, for he is traveling to pray and not for his own personal needs (Or L’Tzion there).
It seems that before praying, l’chatchilah a person should not even leave for a trip that lasts only half an hour. If there is a minyan in one’s area, it is preferable to pray with it instead of traveling to his workplace to pray there, for there is reason l’chatchilah to maintain that even a trip of half an hour is considered traveling before prayer, especially if that is the regular road he takes to work.