(originally published to Helium writing site, now gone)
A number of countries and continents use a rating system to grade the difficulty of their ski trails. Among these are North America, Europe, Japan, Australia and New Zealand. North America uses a series of colored shapes to advise skiers of the degree of difficulty they will encounter on each trail. There are five different ratings: easiest, intermediate, difficult, expert and exceptional expert.
Gradient is the main consideration in giving a rating to a particular slope. Trail width, snow conditions and how often a run is groomed are also taken into account. Each ski resort assigns its own ratings, there being no overall governing body. This can mean some inconsistencies between resorts.
A sign with a green circle indicates that the slope has the easiest level of difficulty. These are usually suitable for beginners and novice skiers as well as occasional skiers who might prefer the easier slopes. These trails are normally wide and well-groomed by ski resort snow cats at least every night. Gradients range from 6 to 25 percent (a gradient of 100 percent is equal to an angle of 45 degrees). Resorts with a large number of green circle trails include the Inn at Beaver Creek, Colorado; Sonnenalp, Vail, Colorado; and Sun Valley Lodge, Sun Valley, Idaho. The Little Nell, Aspen, Colorado has no beginner slopes.
Trails with a blue square designate an intermediate level of difficulty. These slopes have gradients between 25 and 40 percent, and are usually groomed. They are normally the most popular trails at most resorts. Many of these slopes may be somewhat chopped up at certain times of the day, depending on how often the snow cats are brought out. Most resorts have a large number of blue square runs.
A black diamond suggests a slope that is regarded as difficult. They tend to be steeper than green circle and blue square trails, with a gradient of 40 percent or greater. Traditionally, these slopes were often not groomed. However, modern snow cats are quite capable of the job and most people expect runs to be groomed more frequently. The majority of resorts have plenty of black diamond trails.
A slope with a double black diamond is more difficult again and is regarded as suitable only for expert skiers. These trails can be very steep and hazardous. They might be narrow, in a windy area, heavily wooded, or have steep drop-offs. This rating was introduced in the 1980s due to technological advancements in the construction and maintenance of difficult tracks, their increasing popularity with expert skiers, and for safety considerations by trying to keep all but very experienced skiers off the more dangerous slopes.
Less common are triple black diamond runs for exceptional experts only. These trails are even more difficult and hazardous than those rated as double black diamond slopes. Black Hole at Smuggler’s Notch, Vermont has some of these slopes. At certain resorts, unrated slopes can be found that are around the double or triple black diamond degree of difficulty. A handful of thrill seekers who are usually highly competent experts ski unrated slopes that are probably better defined as cliff faces with gradients of 150-250 percent or more.
Most types of trails are offered at the majority of leading ski resorts. Many resorts only use three ratings rather than four or five. Easiest, intermediate and difficult are used at, for example, the Inn at Beaver Creek, Colorado; Fairmont Chateau Whistler, British Columbia, Canada; Sun Valley Lodge, Sun Valley, Idaho; and The Peaks at Telluride, Telluride, Colorado. Easiest, intermediate and expert ratings are used at Stein Eriksen Lodge, Deer Valley, Utah; Topnotch, Stowe, Vermont; and Sonnenalp, Vail, Colorado.
Occasionally, there are certain variations to the five standard ratings. Some trails have a sign that is a combination of two ratings, for example, a black diamond inside a blue square suggests the slope is between intermediate and difficult. Two adjacent blue squares, such as at Canada’s Mont Tremblant, mean the same thing. At Summit County, Colorado, resorts use a double diamond sign with an “EX” in the middle to indicate greater difficulty than a standard double diamond.
Trails that offer obstacles such as jumps and halfpipes are called terrain parks and are marked with an orange rectangle with its corners rounded. Terrain parks also usually use one of the standard ratings, for example, a blue square or black diamond, depending on the degree of difficulty of the obstacles.