@edgarblythe,
We have that in common as I used to design/specify the ramps. I don't now remember all the details - close, but no cigar re number of feet and grade, thou the numbers may come back.
My most interesting one was for a landscape I did for (I think it was) the first AIDS house in Los Angeles, or so it seemed. I was asked by an architect pal. That involved ramp design that took ease into consideration.
The architect pal was the lover of an architectural historian who had been part of a project I was the coordinator of. Through him, I got connected to some of the people trying to help folks in trouble in downtown LA. I didn't do much, stuff in my life and work going on, but I did design a landscape for one of those good people, a small house, no charge my lady. But through him I saw more and more.
Later, the architect, with whom I'd worked before a few times, hired me to design landscape for the LA Times building.