I agree about the feeling of "plunging" quickly into trouble. Not only is the train transitioning from one "portal" (through the tunnel), to another, but the people are too absorbed in themselves, in the mechanization of their lives (represented in their work) to see what is fully ahead, as they are glimpsing from a side angle. And I was struck by the sense of collision when the second train barreled towards "us" in out first person point of view.
Yes, I thought the same thing. The children playing the "death" game, ignoring the woman's fears. The careless way Elsie stepped into the street, and then bouncing the ball off of the poster as if she's almost mocking it. Interesting observation!