[Dr Nevergold]

BTW all this rail terminology can be confusing. I actually have referred to some inaccurate terms.

When I say "in-grade" what I should be saying is at-grade rail connections where the rail is on the ground and occasionally (or entirely) goes within traffic.

Its possible to have an at-grade rail line, but mostly within its own right of way. That is sufficient, but the problem with Pittsburgh's neighborhoods is that they are too dense and too urban to have an at-grade service running right through these urban districts. Only at spots between the districts would this be feasible (for example, from where it exits underground at the South Side Works and would cross the Hot Metal bridge, it could remain above ground until it gets to Oakland). This could take some significant costs out of it rather than doing at tunnel bore for the entire project.

Its entirely feasible.