I lived and worked downtown for a long time.
Anyway, I did some quick maths. Your average parking spot is 8' x 18'. X 40k = 5,760,000'
The boundaries for "downtown" are roughly 3150' x 6600' = 20,790,000'
That means 27.7% of "downtown" needs to be reserved for parking. Probably more, actually, because of vehicles that come and go during the course of business. Can we round up to an even 30% of all space downtown is solely for parking? Sure.