HERAT, Afghanistan — Over the course of an hour on a recent night, the bus waiting in the Herat station filled with passengers. Mostly young men, they had no luggage, just the clothes on their backs, maybe a bag with some bread and water for the long road ahead of them. That road is leading them to Iran.

Every day, multiple buses rumble out of Afghanistan’s western city of Herat, carrying hundreds of people to the border. There they disembark, connect with their smugglers and trek for days, sometimes crammed into pickup trucks bumping through wastelands, sometimes on foot through treacherous mountains in the darkness, eluding guards and thieves. Once in Iran, most will stay there to look for work. But a few hope to go farther.

Afghans are streaming across the border into Iran in accelerating numbers, driven by desperation. Since the Taliban takeover in mid-August, Afghanistan’s economic collapse has accelerated. In the past three months, more than 300,000 people have crossed illegally into Iran, according to the Norwegian Refugee Council, and more are coming at the rate of 4,000 to 5,000 a day.