Zaceman, you're right in your comment on the first photo; the streetcars ran in the subway and lower deck of the D-S bridge from its opening until the end of service in 1954. I'm not absolutely sure, but I think the structure in the right foreground of the photo may be one of the subway station entrances. In the right middle distance the piers are in place for the Union Terminal Viaduct (now used by the Rapid to the West Side), but the structure hasn't been finished. It was completed in 1929. Although it's hard to tell from the distance, there may still be scaffolding around the top of Terminal Tower; I think this photo was taken at about the same time as the photo of the tower under construction.
Marvelous collection of photos. If you haven't attended the bridge-subway tour, I recommend it. If they follow the established pattern, the next date will be Saturday of Labor Day Weekend; you can find out for sure from the office of the Cuyahoga County Engineer.