Afaik, rail companies own the air rights above that corridor. They know what they have and what it is worth. Even if government expropriates, rail companies will push for (and probably get) land prices suitable for a row of condos. That is in the ballpark of $300 per buildable sq ft so in the ballpark of $15,000/sq ft of air rights above the rail. The stupid rail deck park was going to be 20 acres. The cheque to the rail company would be on the wrong side of $10B. You haven't even built anything yet (and that was a relatively small park, not the entire corridor). Now, if government changed laws to make that air space worth less (eg. no structures allowed in the area), then expropriated, then changed laws to allow construction, it could be a fight over bad faith but would probably save billions.