Does the traveler shorten the prayer alone, or complete it with the congregation?

Question:
If a traveler is alone near the mosque, does he shorten the prayer or pray with the congregation?

Answer:
If he is alone, he prays four rak'ahs with the congregation; he does not shorten the prayer unless he is with his "brother" or two or more people.
As for if he is one person, no, he does not pray with the people; the congregation is obligatory; he prays with them and completes the prayer.