A major earthquake hits. Just as you've practiced in disaster drills, you evacuate. Making it to a safe place, you let out a small sigh of relief.
But it's not over yet. Now you've got to make your way home, perhaps through a devastated city and at night.
Itsuki Nakabayashi, a professor at Tokyo Metropolitan University and an expert in city planning and urban geography, estimates that 3.7 million people might be stranded in Tokyo if a magnitude 7 earthquake strikes the city during the day. He calculated the figure based on the number of people who commute in from up to 20 km away.