There may be good policies or reasons not to scatter the population across every back road in the area. I don't know.

The idea that it is not feasible to move the entire population of a city on the highways may just indicate reality, not somebody "screwing up."

I could imagine a highway system designed to exhaust Houston of population in a few days, while still permitting rescue and supply vehicles to circulate--and NO, you can't do it with helicopters--but who would pay for it? And where would they put the extra lanes in the many areas that are built up to the freeways?

A typical dirty bomb will create a lot more panic than actual hazard. Unless you're within a few blocks of it, there are excellent ways to shelter at home.

Too bad somebody obliterated our national Civil Defense system.