Semi-trucks are some of the longest, biggest, and heaviest vehicles on the roads. Semi-trucks -- and here's what "semi" means on a semi-truck-- are wide, averaging 8.5 feet, and can reach 70 to 80 ...

The average miles per gallon of a semi-truck is bad enough when barreling down the highway — somewhere in the range of 6-8 MPG — but things don't look much better when the 18-wheeler's at a standstill ...