Dont know, but driving at 55mph saves more fuel that driving at 75mph.

Changing Interstate speed limit to 55mph would not save any fuel, since noone would actually drive at those speeds.

I am personally know to drive fast on interstates, and 50mph on 55mph highway next to my house. (not actually obstruction traffic, I always take right lane and cruise there)

Its just another political manuver to put some as****e in a seat somewhere.