Acreage of Highways
Just how much area do USA highways take up?
A USA highway is typically 200 feet wide (including shoulder and righ-of-way) - 76 feet in minimum width with shoulder for 2-lane highway, plus whatever land is taken until land can be used for applications other than right-of-way. Thus, there are ~24 acres covered by US highways per mile or highway length.
24 acres per mile means about 1M acres based on the length of USA Interstate Highways and USA Roads.
For comparison, it would take 100x100 miles to power up all of the USA's electric needs.  This is about 7 million acres. Must says that the battery to store all of this would be 1 square mile.
Thus, just using highway right of ways would provide 1/7 of the USA's electricity!
- Roads are 4M miles. Only 1.2% is interstate highways.