Finally: An answer to the question of what happens at the Dedham line when the radioactive monster, awakened from its long slumber by a mid-Atlantic earthquake, attacks Boston and we are all forced to take those emergency evacuation routes that head into our neighboring town:

Dedham police will block off major thoroughfares to keep us moving out of Dedham.

We learn this from Brian over at MyDedham, who called up Dedham's Finest after reading about that woman running all the evacuation routes:

... Our strategy, I guess, is to make all these refugees Westwood's problem. ...

Earlier:
I try to evacuate but am swept away on 128.