Flooding from Sandy caused more damage than first thought to the two tunnels that carry trains under the Hudson and East rivers, Amtrak said Thursday.
The railroad made the announcement as it released an engineering report detailing the damage to structural components from saltwater that inundated the two tunnels during the 2012 storm.
Crews have been making some repairs on weekends but Amtrak said the extent of the damage required longer closures that would result in delays for passengers on Amtrak, Long Island Rail Road and New Jersey Transit. All three share the tunnel tracks.
The repairs underscored the need for a new tunnel under the Hudson River known as the Gateway Project, said Amtrak spokesman Craig Schulz.
He said it would take a year to do the prep work for closing an East River tunnel, then another year to do the work. The railroad's preferred option for the Hudson tunnel would be to build the Gateway tunnel before closing the Hudson tunnel, Schulz said.
The report "puts an exclamation point" on the need to build a new tunnel, said Schulz. "That is absolutely our best-case scenario."
It "would allow us to move the existing traffic into a new tunnel with two tubes, shut the existing tube down, do the necessary work and then ... eventually have a 4-track between New York and New Jersey," he added.
Repairs on the Hudson tunnel would create major headaches for riders, Schulz said.
"The idea of going from 24 trains an hour to six trains an hour is really something that no one wants to see," he said, adding that it would create a ripple effect on the whole Northeast Corridor, from Boston to Washington.
The report did not offer a firm timetable for the repairs but recommended that the work be done in phases to get it done as soon as possible while minimizing disruptions to passenger service.
Officials said they expected insurance to cover the estimated $689 million cost of the repairs.
While the report found no evidence that the tunnels were unsafe, it did find that the salt water has caused significant damage to the track, signal, electrical and mechanical systems.
Only two of the four tubes of the East River tunnel, which runs from Penn Station to Queens, were damaged in the storm. The Hudson River tunnel consists of two tubes that extend from North Bergen, New Jersey, to 10th Avenue in Manhattan.
About 400,000 passengers ride trains through the tunnels each weekday.