A fleet of cleaner-burning buses that cost less to operate and sport colorful photos and graphics letting tourists know about Central Coast attractions went into service at Hearst Castle on July 31.

Silverado Stages Inc. of San Luis Obispo is investing $3.5 million over a 10-year contract to supply the buses. The fleet of 14 57-passenger buses and two 29-passenger buses for the disabled carries about 650,000 tour-takers per year from the visitor center at the base of the hill along a twisting five-mile road that climbs 1,500 feet to the top of La Cuesta Encantada (“The Enchanted Hill”).

Silverado, which started as San Simeon Stages with a single bus in 1987, replaced Ohio-based First Transit Inc., which, according to its corporate website, is part of FirstGroup, the world’s leading transportation corporation. Silverado chief executive officer Jim Galusha said the charter bus company had 12 buses when he acquired it in 2004. It is now the largest in California and 21st largest in the nation. It has 116 buses and employs 200 people.

The First Transit buses also burned natural gas, but were conversions. The Silverado buses are 2012 models manufactured by Blue Bird Corp. in Georgia.

Natural gas-powered vehicles emit about 5 percent as much soot as diesel-powered ones, Galusha said, and operate at about one-third the cost of gasoline. Only about 1 percent of the world’s 12 million compressed natural gas vehicles are in the U.S., largely because of a lack of fueling stations, he added.

The wrap-around advertising on each bus combining photos and graphics was applied at the Blue Bird plant in Georgia. Various tourism groups paid $5,000 to have their images on the buses for 10 years. Those participating are: the Cambria Tourism Board; Morro Bay Tourism Bureau; Travel Paso Robles; the San Simeon Tourism Alliance; Solvang Conference & Visitors Bureau; Ventura Port District; the county Air Pollution Control District and Central Coast Clean Cities Coalition; Central Coast Tourism Council; and Buellton Chamber of Commerce.

“We came to the realization that you don’t need to advertise Hearst Castle — (the visitors) are already here,” Nick Franco, State Parks district director, said at a reception for the new buses at the Castle on Wednesday.

He thanked the tourism organizations for “stepping up and sponsoring a bus,” and he said they’ve “gotten positive response from visitors.”