The borrowing limits affect the timeline, but I'd be surprised if they affect the cost in any measurable way. Bond interest rates are so low for something like

The borrowing limits affect the timeline, but I'd be surprised if they affect the cost in any measurable way. Bond interest rates are so low for something like this that after adjustment for expected inflation they might as well be zero. Above ground does matter. Grade separated still mostly works from a transit perspective, but there are other concerns: how they affect surface traffic, how they can be affected by marine traffic, etc. Underground is more expensive but still demanded for a reason, and we are still paying >2x per mile for above ground vs what Paris paid for underground lines.