A low-emission prototype is a modern version of the traditional Yellowstone National Park tour bus.
Developed by the Idaho National Engineering and Environmental Laboratory, the departments of Interior and Transportation, and private industry, the bus uses alternative fuel and complies with the Americans with Disabilities Act (ADA).
The bus will carry several optional engines burning alternative fuels such as natural gas, propane, ethanol, and biodiesel. Currently, the CNG engine displaces 6.8 liters and meets ultralow emission standards with 0.5 ppm of nitrous oxide. The chassis can carry the equivalent of 40 gasoline gallons of compressed gas.
The passenger area of the bus sits low so that no steps are required for entry. An entry ramp can extend to accommodate passengers in wheelchairs and strollers. As a modern interpretation of buses that were commonplace in Yellowstone and Glacier National Parks in the 1930s, the bus includes a roll-back top and rounded back. Modern touches include an air and kneeling suspension for a smooth ride as well as audio-visual capabilities.