ADA guidelines

Slope Grades (Anat)Generally speaking, no running slope should exceed 5% grade if it runs longer than 200'. I would call that a moderate grade. Then there's the 'steep' section which allows up to 12.5% grade, but specifiies for different grades how long those grades may persist and how long of a 'flat' interval must be provided in-between slopes.

Below are guidelines, an accessible path would meet these minimum technical provisions: Clear tread width: 36" minimum Tread Obstacles: 2" high maximum (up to 3" high where running and cross slopes are 5% or less) Cross Slope: 5% max. Running slope (trail grade) meets one or more of the following:

• 5% or less for any distance.
• up to 8.33% for 200' max. Resting intervals no more than 200' apart.
• up to10% for 30' max. Resting intervals 30'.
• up to 12.5% for 10' max. Resting intervals 10'. No more than 30% of the total trail length may exceed a running slope of 8.33%. Passing Space: provided at least every 1000' where trail width is less than 60"

http://www.ada.gov/regs2010/2010ADAStandards/2010ADAstandards.htm#c4-- Point 402.2

High hills in Seattle http://www.seattle.gov/transportation/steepest.htm