Tokyo's population is about 4 times that of Houston. So fine, instead of running 3000 trains a day from the central station, you can run at least 750?

That's what life would look like if people in the US actually used trains on a regular basis.

In any case, all I'm saying is that if a massive number of people need to be moved, trains can scale well, additional reserve capacity can be deployed during evacuations, and it's also a lot safer than having hundreds of thousands of people taking to the roads in bad weather.