There are many advantages of adding alternative energy fuels in the fleet. The main advantage is that alternative fuels are very inexpensive; there are many types of alternative fuels for example bio-fuels, hydrogen fuel and solar energy etc. Standard fuel sources include nonrenewable energy sources such as petroleum-based products, natural gas, coal, propane and nuclear power. Alternative fuels on the other hand, refer to any unconventional source materials that include bio-fuels (e.g., biodiesel, ethanol), hydrogen, wind power, hydroelectricity, geothermal energy, and solar power (Kemp, 2006).