The Trail Difficulty Score (TDS) is Ski.Vacations proprietary rating of ski trails as to how challenging they are to get down. We use a scale of 1-9 with 1 being the easiest and 9 being the hardest. This scoring is similar to one used by the PSIA (Professional Ski Instructors of America) when rating sking ability. Many ski schools around the US use a version of this (Europe often uses a 1-6 system). Again with a 1 being an absolute beginner and a 9 being able to "Ski all slopes in all conditions".
The TDS is international in that a score is meant to be comparable from country to country. A trail scoring a 4 in Austria should be as challenging as a 4 in New England and vice-versa. While a ski area may rate a trail using the traditional Trail Symbol of a double diamond it could be the case that that same trail at another ski area would struggle to be a diamond at all. Some ski areas located in smaller mountain ranges may not have any trails scoring above a 7 while more extreme mountains will feature many 8's and a handful of 9's.
In recent years many US ski areas have gone beyond the tradtional Green Circles / Blue Squares and started using Double Squares and even Diamonds in Squares. To add to the confusion Europe and South America also use the color red and no symbols at all. We hope our TDS will allow skiers/snowboarders to compare trails they know well to one they may visit on vacation and know that Blue Square back home is nowhere near as hard to get down as that Blue Square they encounter for the first time on holiday.
A trail rated a 1 is most likely a learn-to-ski area with little to no slope, well-groomed and wide with lots of room. Typically this kind of trail is set off so as to get little to no traffic from other skiers besides those learning to ski/snowboard. Trails rated a 9 are few and far between. These types of trails are likely to be the hardest trail at the most challenging ski areas. Most people have no business attempting these trails.
When scoring a trail we look at the symbol assigned by the mountain, our own experience skiing it, and the scores from local experts and professional skiers/snowboarders. We also allow you to vote on the TDS. If you feel that our score is too high or too low vote and we will take that into consideration when looking at adjusting scores. Look for the Ratings Section for each trail. Please vote "stay the same" as well if what we have as a TDS matches your experience.
Here is a great detailed article on comparing https://www.nytimes.com/2015/12/13/travel/5-things-skiers-may-not-know-about-the-trail-map.html