Alpine skiing, alternatively referred to as downhill skiing, ranks as one of the most popular winter sports in the world. In order to differentiate the level of experience a skier needs to safely negotiate a specific ski run or trail, resort owners have established a rating system that makes use of different colors and shapes. Trails marked with a green circle are appropriate for skiers with a basic ability but not much experience. Trails marked with blue squares, meanwhile, are better suited to intermediate skiers. On most mountains, a black diamond represents the highest level of difficulty for a trail. However, some resorts and mountains make use of the double black diamond rating in order to distinguish a particularly challenging trail that should only be tackled by experts.
For amateur and intermediate skiers who have yet to reach the black or double black diamond level, it may be hard to understand exactly what challenge these trails present. Double black diamond trails feature very steep slopes, resulting in extreme speeds that may be hard for non-advanced skiers to handle. By comparison, most black diamond trails have a steepness grade of about 40 percent. A trail may also receive a higher difficulty rating due to natural obstacles, exposure to wind and ice, and various other hazards.