Three viaducts

"Three viaducts." This is Wynkoop and 15th Street, 1978. We're looking at the 15th street viaduct (built after 1937), the 16th street viaduct (built before 1937), and in the very far distance, the 20th street viaduct. All three have been demolished. Of interest is the Barteldes Seeds building entrance onto the 16th street viaduct. You can see it from the Tattered Cover corner (2012). It's weird to see a door up there! I was up on the viaduct in 1978, photographing toward Cherry Creek, not Barteldes. I wish Cyril Norrred, the WPA photographer, had looked the other way, toward Union Station, from the viaduct.
How did people get off the streeetcar and enter the Seeds building? (This will always be the "Seeds" building to me.) Could they park on the viaduct? Is it true that the 2nd floor door was the main public door? Oh, to go back in a time machine...