Based on the portal and the build dates it might also be Stringer's Ridge.
I have pics of my grandparents taken in/about the 1920's, standing with friends in front of what I believe is the original, one-tube McCallie Tunnel, viewed from the west side looking east. They lived down Dodds Avenue at the time (where the funeral home is now) with her mother, Ida Kelly. Note the street is still gravel! The right side of the concrete form looks the same, though the top looks different (could have been altered in the addition of the new tube). It looks like the Cherokee Blvd. tunnel, also, but the pic shows much more earth above the tunnel than the Cherokee Blvd. one has, so my guess is they were built around the same time and/or by the same people. I'd appreciate any research on this that anyone would care to do.
BTW, while we're on the subject of bridges, my great-grandfather Joe P. Kelly worked for the Converse Bridge Company in Chattanooga at the time of his death in 1912. They specialized in metal truss bridges.
Only one of these two tunnels was built in 1950. The other one had been in existence for some time prior to 1950. Some research will, no doubt, reveal when the first tube was constructed. Sorry I have no information as to that date.