zion canyon scenic drive provides access to zion canyon. traffic congestion in the narrow canyon was recognized as a major problem in the 1990s and a public transportation system using propane-powered shuttle buses was instituted in the year 2000. as part of its shuttle fleet, zion has two electric trams each holding up to 36 passengers. usually from early april through late october, the scenic drive in zion canyon is closed to private vehicles and visitors ride the shuttle buses.