The city hired the consultant Parsons Brinckerhoff in early 2011 to study the merits of extending the subway, shortly after New Jersey Gov. Chris Christie canceled the planned "Access to the Region's Core" cross-river tunnel project, which was a blow to those who believe the region is hampered by the limited capacity for trains crossing the Hudson between Manhattan and the suburbs.
If the Hudson Yards project continued without the casement, officials said, it would block access for any new tunnel projects looking to serve Penn Station's existing tracks.