Fingertips:

1. Eisenhower Interstate System
(Matching tags: Preparations for War,Airstrips,United States,Eisenhower Interstate System,Roads,Factoids,Highways)

The Eisenhower Interstate System requires that one mile in every five must be straight.  These straight sections are usable as airstrips in times of war or other emergencies.

2. Statistics About Paved Roads in North America
(Matching tags: Canada,United States,Roads,Highways,Factoids)

Chances that a road is unpaved: in the U.S.A. . = 1% in  Canada = ...75%