Should a traveler shorten his prayer if the time for it overtakes him while he is within the buildings of his hometown?

If a traveler catches the prayer in his town before departing, he should not shorten it. However, if he has departed and the call to prayer is made while he is still within his town's boundaries, and then he prays on the road, he should pray it as two rak'ahs. The key factor is the performance of the prayer: if it is performed during travel, it is shortened; if it is performed while resident, it is completed.