This is not an answer to the Eliza Furnace-Swinburne Street issue, but an alternative - the Chateau Trail access area known as The Bastille, 2000 Westhall Street, Pittsburgh, PA 15233, has car parking, portapotty, and good bike trail access. It's also colocated with SCI-Pittsburgh (a/k/a Western Penitentiary), which puts the area under video surveillance and an armed guard drives through the area every two minutes.

The patrol is there to secure the prison, not the trailhead, but it does have a calming effect nevertheless. It's as close to secure parking as I've found at a trailhead.
As I said, it's not a solution to the broken window issue, but if the Bastille Trailhead isn't too inconvenient it may provide what you need. From there, you're 2.5 miles on the Chateau Trail to the Ft. Duquesne Bridge bike ramp. Cross the Ft. Duq Bridge and you're in Pt. State Park.
You guys all know this, but from there you cross the Ft Pitt bridge for the SouthSide Trail, or take the Strip District Bridge out to the Cork Factory, etc.
Just fwiw. Merry Christmas to all.