I have a question about gas mileage, how come going on the highway at 70 mph I can get up to 30 mpg, but at 60 mph I only get 20 mpg? Just wondering? Taking it a step further if cars can get better gas mileage at higher speeds why don't they raise the speed limits on highways so we can use less energy(being gas)? Just wondering?

I've wondered about that too; they always say going faster reduces your gas mileage, but mine always goes up when I go faster.

Not all vehicles achieve higher mileage at higher speeds.
And not all vehicles get the same mileage at the same speed, either.
What we are driving, the posted speed limit, is an assumption that all drivers are also paying attention, thus avoiding stop-and-go driving.
A smoother flow of traffic with shorter stops will go a long way to seeing higher MPG's.

The MAIN reason they don't raise the spped limit is because of safety. Hit you at 55 you might have a better chance to survive. without causing a chain reaction accident on top of it. At least, that's part of the theory, if they could get people to obey the speed limit and not tailgate!
Also when you are driving freeway it is at a consistent speed with very little of the stop-and-go that takes up a lot of gas.
I have read that the actual best mileage is between the speeds of 45 to 55 MPH.