The double-black diamond (hyphenated or unhyphenated) sounds like something most of us would not want. But what is it?<2016 “Pittsburgh logged Day 1 of Uber’s self-driving car experiment.
A few of the ride-share service’s most loyal users are taking part in the pilot program, operating in a few square miles of the city’s downtown.
During our own reporter’s test ride, a safety engineer in the driver’s seat took control of the car several times — to avoid speeders or when a truck suddenly backed out in front of them. “Pittsburgh,” an Uber officer said, “is the double-black diamond of driving.”—New York Times, 14 September>
According to Wikipedia: it is a skiing term:
BLACK DIAMOND: Amongst the most difficult slopes at a mountain. Generally, Black Diamond trails are steep (40% and up) and may or may not be groomed. [For advanced skiers]
DOUBLE BLACK DIAMOND: These trails are even more difficult than Black Diamond, due to exceptionally steep slopes and other hazards such as narrow trails, exposure to wind, and the presence of obstacles such as steep drop-offs or trees. They are intended only for the most experienced skiers.
This trail rating is fairly new; by the 1980s, technological improvements in trail construction and maintenance, coupled with intense marketing competition, led to the creation of a Double Black Diamond rating.
(See Wikipedia) for slope ratings.)
Ken Greenwald – September 17, 2016