Hi Rob,
Some of us are using the "old" British system of describing slopes. If a road rises 100 feet vertically in a horizontal distance of 400 feet, that's a 1 in 4 slope (and pretty d*!n steep!). The modern way, which is gradually creeping in, is to express it as a percentage. 1 in 4 is 25%. 1 in 10 would be 10%, etc.
Our most detailed national mapping system, Ordnance Survey (OS), has two "steep hill" markers on the maps. A single arrow across a road shows a hill of between 1 in 7 and 1 in 5. (14% to 20%). A double arrow is for steeper than 1 in 5.
Many of us never encounter a hill as steep as 14% in our cycling lives, so we don't get that information from the OS maps. Hence discussions about how to calculate gradients, in order to assess bike performance. Search the forum for "gradient" or "slope" and you should come up with some relevant threads.
How do you measure slopes in USA? Percentages?
Regards,
Mary