The SB path track can easily go over 21 on a partial Viaduct over the Northbound Lanes. If they really wanted to build it, theyd find a way. Highways and roads are constantly realigned whenever the government wants to build rail or highways. Also keep in mind when the South Street station reactivation was dismissed that area was not seeing much Redevelopment. Since then, a major apartment building has been built right next to the old station on what used to be a former rail yard. You can still see the bridge that carried the siding over South Street just east of the bridge carrying the 4 main tracks. Developments like this will once again make the South Street Station viable.