Median Income

So I drove over 2,000 miles in the past couple month on this nation's fine interstates and something occured to me. Medians are wasted space. Sure they keep driver from careening into each other and make good places for deer to regroup before attempting to cross the other two lanes. But is that really their best use?
Take the drive from Charlotte to Atlanta. 200+ miles of interstate. Medians are about 30 yards wide. So that's 90 feet times 200 miles times 5,280 feet in a mile. That's 31,680,000 square yards. Or over 6,500 acres. That's a nice size farm kids. Why don't we grow something instead of having grass or trees? Just wondering.