Travel Power: The North Vietnamese have conditioned themselves for a war which, according to official Hanoi predictions, may last 10 to 20 years. While the people live their daily lives under anti-aircraft fortifications and machine guns in upper-story windows throughout the towns, commerce and industry continue. Despite the war and the bombings, this tramline in Hanoi continues a cheap means of transportation to the populace. One woman is seated, left, on the opening to a bomb shelter