The entire area was once home to the ASARCO Tacoma Smelter. The smoke stack and part of the smelter were uphill from the tunnel. I dont recall which came first the tunnel or the smelter, but millwork and massive piping/ducting was on that narrow space just over the tunnel. You probably saw the adajacent but lower tunnel next to the railroad tunnel and that was the street. It was just a couple years ago that the new street bypassed the old tunnel as part of the site cleanup. Just google Tacoma Smelter Photos and you will see the before and after shots of the area. When the smokestack was built in 1917 it was the largest in the world. As you would expect the whole area was highly contaminated with lead, copper and arsenic; now mostly cleaned up.
Roger Beckett