Wild Alpine uses the D Scale for Skiers and Splitboarders to better understand your experience in the mountains. Click here for the scale. Continue reading for a complete explanation.
“D System – Système” and “D Scale” for Rating and Grading Backcountry Ski and Snowboard Mountain Descents
Edited by Louis Dawson and Andrew McLean. Latest revision of this page: August, 2010.
The “D System” described here is a linear method of rating, grading, or describing how difficult a slope is to ski or snowboard DOWNHILL, how dangerous the route is, and how long it takes to climb. In other words, the D System COMPARES the difficulty and danger of routes to one another.
The term “D” is shorthand for words such as descendere, detail, détail, descent, détaillé, detalle, difficulty, descente, downhill, down, drop, difference, degree, etcetera. As a nod to cognates, the word “detail” is the same in French, German and English, and is “detalle” in Spanish, so perhaps the D System could be called the DETAIL System if one wishes to be international, as said en français.
Before reading farther, please be aware that the D System has three parts or scales.
D Scale Route Ratings (détaillé, difficulty)
R Scale (rischio, risk)
Grade Scale (length of route, longueur d’itinéraire, as a roman numeral)
The D Scale is the most important part of the D rating and grading System (and may be used without the other scales). Routes are rated on the D Scale according to the difficulty of skiing or snowboarding — such difficulty varies mostly because of terrain features and slope angle, but many other factors play a part as well. Thus, most importantly, routes are rated by public consensus of how routes compare to each other as to technical difficulty (as in rock climbing ratings).
Difficulty “D” Rating Scale
In the D System, routes receive a “D Rating” on the “D Scale” (shown above) according to their toughest terrain and steepest angle. If a route has 3,000 vertical feet of low angle skiing, but starts with a 50 degree headwall above a bergschrund, it would be rated for the headwall and for negotiating the ‘schrund (though a route with a similar but longer crux section might rate one or two steps higher on the scale.)
Routes generally increase in difficulty on the D Scale as slope angle increases, but slope angle is only part of the picture. In other words, a route that’s a few degrees lower angled than another could actually rate higher on the scale if it had terrain features that made it tougher to descend. Thus, In the case of routes with similar slope pitches, terrain features and obstacles would ratchet a route higher or lower on the D Scale, but length of steep crux sections would play a part as well. Terrain features of concern include but are not limited to: tree skiing (open or tight), narrows, melt or avalanche runnels (if usually present), drops, cliff jumps, traverses to link sections of a route, narrows, mandatory rappels, etcetera.
Since this is a linear system of describing difficulty, some routes fall close to each other on the scale and their rating may be debatable. To help refine ratings, factors such as the total length of the route, length of the steep sections and amount of tough terrain may be considered as well. Again, as this is a linear system, public consensus will provide the final rating of routes. In other words, rating routes for the D Scale part of the D System should first be based on terrain features and slope angles, but should allow other factors to place the route in the continuum of the rating scale. In the end, just as in rock climbing difficulty ratings (5.x), eventually there will be little need to describe criteria for each rating, as numerous routes will serve as examples.
The D System is inclusive — it is designed to work with the diverse culture and languages of worldwide ski and snowboard alpinism. Hence it uses letters and numbers instead of any specific language (the letters “D” and “R” translate to numerous related words in many languages, see intro above). The D System is intended to work for routes anywhere in the world. More, all rating scales (grade, D and R) in the D System are open ended, thus allowing for development of the sport without re-rating routes to fit in a closed end scale, or contriving ways of extending a scale.
What Doesn’t Count on the D Scale
– The D Scale is NOT a rating scale for route length or approach length (see “Grade” below), though a route with a longer crux would generally rate higher than with a shorter but equally difficult crux.
– The D Scale is NOT a danger rating system (danger is rated with the R Scale explained below), but it still may communicate hazards intrinsic to the slope angle and terrain features. More, in the case of steeper routes, if two routes had everything else equal, but one involved extreme hazard such as skiing a few feet above certain-death cliffs or the possibility of a long sliding fall with no safe runout, such a route could be ratcheted up one D Scale grade higher since skiing such terrain is more difficult because it requires no-fall technique with limited maneuvering space. Conversely, objective hazards such as an icefall above the route have no influence on the D Scale rating of a route (but rather are rated with the R Scale covered below).
– The D Scale is NOT a slope angle rating system. While routes on the D Scale usually fit in angle categories such as “the 45 degree range,” a route could be slightly less steep than another yet still rate higher because of difficult terrain. In other words, there is some overlap in slope angle when routes are rated. Nonetheless, slope angle IS important, and overlap should only occur within smaller angle ranges. For example, a 30 degree route with tight trees (probably rated D5) could never rate higher on the scale than a 45 degree route with no terrain obstacles (probably a D9). If guidebook writers, alpinists or barstool conversationalists are concerned with exact slope angles, they can always append an exact slope angle to a rating, or include it in a route description. Another reason not to make a god out of slope angle is that it may never have been accurately measured, especially in the case of difficult routes that have only been done a few times.
Historical note about slope angles: In the formative days of extreme skiing it was all about slope angle, as most descents were done on open slopes or wider couloirs where angle was the determining factor of difficulty. Thus, it was easy to rate route difficulty based on slope angle alone, as is done with the S System (see end of this page). Today’s extreme skiing explores terrain where features other than slope angle frequently play a part in how hard a route is. Hence, a modern rating system must combine all factors to rate difficulty on a linear scale. Nonetheless, ski alpinists still tend to emphasize slope angle when communicating about routes, so it’s important to keep that in mind.
Route Length “Grade” Scale
In the D System, routes optionally receive a Roman Numeral “Grade” rating for how long they take an average party to complete in average conditions — this is virtually the same as that commonly used in North American mountaineering ascent ratings. Again, know that while routes are rated on the D Scale mostly according to the difficulty of the hardest section of the route, a much longer route will tend to get a harder D Scale rating as well as a higher Grade rating.
Grade I routes are usually done in a few hours.
Grade II routes take about a half day for an average party.
Grade III means the trip requires a normal day.
Grade IV routes are the longest normally done without an overnight.
Grade V means the route requires a mega day or overnight.
Grade VI trips usually require a night out or a huge push.
Grade VII is reserved for routes such as those on Denali or Mount Everest.
See examples below for routes with length grade ratings. More than in climbing, the question of how much the approach is part of a ski route’s length grade will no doubt come up while rating ski routes. We’ll leave that detail up to locals and guidebook writers.
Risk “R” Scale
D System routes may also receive an optional risk rating that considers things such as potential for icefall, rockfall, crevasse danger, consequences of a fall on the route, avalanche terrain traps, rocky areas that tend to be hidden by thin snow, and so forth — but is not a rating for avalanche danger (snow instability). The “R” scale (standing for words such as rischio, risque, and riesgo) goes from 1 to 5.
R1 Average backcountry ski routes, meaning the route has little to no objective hazard (other than possible avalanche danger that varies with the snowpack).
R2 Slightly more inherent danger.
R3 Route probably has sliding fall potential if snow is firm, moderate amount of obstacles or features that could cause injury, or moderate exposure to rockfall, tributary avalanches and other dangers.
R4 Route has plentiful hazards such as fall potential, rockfall, crevasses, etcetera. etc.
R5 Reserved for the most hazardous routes.
In the case of average backcountry routes the R Scale rating is optional, and in many cases might not be used.The “R” Scale is more subjective than any other part of the D System. As with all other parts of the D System, the R Scale is intended to compare routes to one another rather than giving a final word on how dangerous a route actually is (this could only be done in a narrative style guidebook description or trip report, if even then). And to repeat: the R scale is not an avalanche risk rating, though it does consider the probability of “tributary” avalanches that threaten the route from above, such as in the case of Himalayan climbing.