Mammoth Cave National Park's commitment to incorporate sustainable initiative into all aspects of its operation has made it the first of 394 National Park Service sites to run all light- and medium-duty vehicles on alternative fuels, including biodiesel, ethanol, and propane autogas. The Kentucky park converted its entire fleet of six buses from gasoline to propane autogas more than a decade ago to transport over 200,000 visitors to entrances of the world's longest known cave system each year.

The buses, fueled by propane autogas, provide such a high-performing and sustainable solution for the park that it is replacing four buses with new Blue Bird Vision propane-autogas-fueled buses later this year.

Domestic, Sustainable Alternative Fuel

In the mid-1990s, Mammoth Cave National Park received a grant from the Kentucky Clean Fuels Coalition (KCFC) — a Clean Cities coalition member — to convert buses to run on propane autogas. The buses make continuous routes from visitor parking lots to four cave entrances across the park and travel a combined 475 miles a day during the park’s busy season.

Propane autogas is the leading alternative fuel in the United States and the nation’s third most common vehicle fuel after gasoline and diesel, fueling more than 270,000 vehicles across the country, according to the Propane Education and Research Council (PERC). Propane autogas is a domestic resource, as 90 percent of propane autogas supplies are produced in the U.S. Fueling with propane autogas helps reduce the country’s dependence on foreign oil.

Vehicles fueled by propane autogas emit 25-percent less greenhouse gas emissions, 12-percent less carbon dioxide, 20-percent less nitrogen oxide, and up to 60-percent less carbon monoxide than gasoline-fueled vehicles. The conversion to propane autogas not only contributes to cleaner air but also extends the life of the buses’ engines because propane autogas burns cleaner than gasoline or diesel and reduces engine wear.

“Fueling our buses with propane autogas matches Mammoth Cave’s mission to be an environmental leader and employ sustainable practices,” said Mammoth Cave National Park Superintendent Pat Reed. “The buses allow us to transport visitors while reducing our carbon footprint.”

High Performance with Reduced Maintenance

The buses’ high performance — combined with reduced emissions, cost, and maintenance — led Mammoth Cave to invest in new propane-autogas-fueled technology. The park recently purchased four new Blue Bird Vision propane-powered school buses to replace aging buses in its fleet through a grant from the Energy Department that was facilitated by the KCFC. The park’s concessionaire, Forever Resorts, oversees maintenance, refueling, and operation of the buses.

“Our engines are getting more years of service with propane autogas,” said Greg Davis, general manager of Forever Resorts. “We haven’t had any problems as far as maintenance is concerned.”

The buses climb the park’s hills with no trouble, and drivers and passengers have not noticed a difference in performance.

“The performance is exactly the same as a gasoline- or diesel-fueled bus; there is immediate acceleration and lots of power,” Davis said. 

The park owns a 1,000-gallon onsite refueling dispenser, while Forever Resorts negotiates an annual fuel contract and manages weekly fuel delivery with a local propane autogas provider. The speed and ease of refueling is comparable to that of gasoline or diesel, and government incentives are available for infrastructure installation.

During busy summer months, the buses use around 80 gallons of fuel daily. All drivers are trained on proper refueling procedures. Even after the delivery of the new Blue Bird Vision propane-autogas-powered buses, the park doesn’t rule out adding more buses in the future.

“We want to continue to provide examples of how to interact in a sustainable way with our environment,” Reed said.

About the Author

Roy Willis is the president & CEO of the Propane Education & Research Council (PERC).

The Propane Education & Research Council was authorized by the U.S. Congress with the passage of Public Law 104-284, the Propane Education and Research Act (PERA), signed into law on October 11, 1996. The mission of the Propane Education & Research Council is to promote the safe, efficient use of odorized propane gas as a preferred energy source through research and development, training, and safety initiatives.