Specifications include, but are not limited to: Heavy-duty buses purchased under this RFP will be low floor, double deck transit bus; and diesel, hybrid, CNG, or electric propulsion system; or any combination thereof. The buses will not to exceed forty- three (43) feet in length, with an overall height of not more than 14 feet including all GPS and communication antennas, as per Washington State Law. Maximum height of antennas is 3 inches. Buses shall have a minimum expected life of twelve (12) years or 500,000 miles, whichever comes first, and are intended for a wide possible spectrum of passengers, including children, adults, the elderly, and people with disabilities. Where brand names or specific items are used in these specifications, consider the term "or equivalent" to follow. The buses must be Altoona tested and meet any other bus testing requirements under MAP-21.