O lord ,that thing has been there forever.I believe they might have been all over town at some point,close to schools and libraries.

Old underground crosswalks. You can find them all over the city in areas where people used to walk alot. We have one in Long Beach going under Ocean Blvd at Cherry Ave that connects people from the park to the beach. It's usually closed off, except on the 4th of July when pedestrians reach critical mass.

Oh!

That *is* an underground crosswalk. I went to Melrose Avenue Elementary school (which is adjacent to that intersection) in the mid-1970s, and we used to cross underneath there. But it was only open at certain times. It used to have a chain link fence just at the bottom of the steps to lock the underground tunnel part, I'm not sure when they built up that big monstrosity to cover the stairwell, too. It was scary as a little kid, and it smelled like pee! Every time we'd enter on one end, we would run and not stop or look back until we got across. No one ever wanted to wait down there very long. But it was one way we could cross Melrose without adult supervision. I seem to remember it only being open during school hours for the children to use, but closed the rest of the time because homeless people went down there. Back then we called them "bums". I think it was originally built back in the 50s, but by the 70s was being used less and less. Another throwback to the 50s when I went to school there were the weekly air raid emergency sirens that would blow at 10:15 a.m. every Friday (which were also located near that intersection). I think they stopped doing that later in the 70s.

So, yeah. It was a safety crosswalk for children to use to walk to school, and probably went defunct in the late 70s or early 80s. At some point after that they added the big fence completely enclosing the stairwell, and it's been sitting unused like that ever since.