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How do they determine how many handicap spots a parking lot is supposed to have? Is it supposed to be a percentage of total parking available?


Yes, that is correct.
My wife being a Landscape Architect mentioned that to me at one point, but also said, there is no rule to WHERE the handicap spots should be, just that there has to be a percentage of the total.
There is a lower limit where you don't have to have any, don't remember what that is though.


1986 Pickup extracab longbed "Woody edition"
SAS - 33's, 5.29's, lockright rear.

02 IS300 SportCross - my "DD"
94 2wd v6 extracab
04 Outback Wagon- wife's/family car