Update: The Strange Unused Tunnel along Carson Street in Pittsbughs Southside has an even Darker History and good reason why it was closed it became known as The Murder Tunnel

With some further research that mysterious Brown Tunnel as it was known along Carson Street which was closed  and bypassed with a set of stairs around 3rd street was done so for a reason.

It became known as the Murder Tunnel
after 2 Italians and 1 workman's remains where found in the tunnel which allowed people to get to homes on other side of railroad tracks to Manor St. which are now long gone.

According to a 1885 description in the Pittsburgh City Directory, Manor street ran from Brownsville (Arlington) ave. to South 17th. Manor street along with a school  was razed in 1932 to make way for the lower extension of McArdle Roadway, from the Liberty Bridge to South 10th Street.