Casinos come in many sizes and shapes: Some float down the Mississippi River, some are on stationary barges that never sail, some are in the middle of a moat, and some are on dry land. Most casino operations either have their own hotel or are supported by a hotel complex. Generally, the casino in a casino-hotel complex, not the hotel, is the economic engine that drives the operation. Las Vegas has over 120,000 hotel rooms. Because the principal target population Las Vegas draws from is over 275 miles distant, gamblers need a place to stay. Atlantic City, on the other hand, has only 25,000 hotel rooms because its principal target market population lives within a two-hour drive. Consequently, most of its customer base is made up of people who are staying for just one day, or day-trippers. This has led to the growth of a previously untapped transportation format, the busing program.