Digging up the Intrerstate is a real possibility. When cities break down and the hordes try to go rural for food, trenched highways will prevent vehicles from moving.

“Shows of force have historically been undertaken mostly by a military actor unwilling to engage in all-out hostilities, but fearing to 'lose face' (to appear weak). By performing a carefully calculated provocation, the opponent is to be shown that violent confrontation remains an option, and there will be no backing off on the principle that the show of force is to defend.

Shows of force may be actual military operations, but in times of official peace, they may also be limited to military exercises.”