If you are organizing a downhill, super D, or cross-country race, you may be using a ski resort as your venue. Ski resorts not only work for this type of event, but they have a need for revenue during their off-season. Their lifts provide shuttling to the top of the trails for your riders instead of vehicles. For spectators, the resort may allow them to ride to the top of the trail if they pay a fee.
Another option for these events and a 4x course is a shuttle vehicle. These should have roof racks or a trailer with bike racks on it.
In either case, you must clearly and repeatedly communicate to the racers when the shuttles are running and when they are expected to be at the start.