Cracks and corrosion from sea water salts line the Amtrak tunnel beneath the Hudson River. Amtrak

Pressure washing, bench wall replacement, direct fixation tracks—oh, my.

Late last week, Amtrak revealed the extent of the damage its New York-area tunnels suffered during Superstorm Sandy, and it wasn't pretty. Seawater infiltrated ventilation shafts during the 2012 storm, flooding train tunnels beneath the Hudson and East rivers that date back to 1910. At some point soon, each of the four damaged tracks (two beneath each river) will have to be shut down to undergo serious long-term repairs. The new engineering report estimates the total cost at $689 million.

Using figures in the full report, which was provided by Amtrak, we charted the repair costs below. The damage falls into four categories: pressure washing ($9 million), crack and delamination repair ($8.3 million), bench wall replacement ($479.4 million), and a complete track replacement ($192.3 million). The $689 million total is spread fairly evenly across the four tracks. The East River tunnel will need $334.1 million in attention; the Hudson tracks, $354.1 million.

CityLab

Let's go a little deeper inside the numbers and see what Amtrak's up against.

Pressure Washing: Long after the seawater from Sandy was pumped out of the train tunnels, salts (mainly chlorides and sulfates) stayed behind to attack the cast-iron and concrete tunnel linings. Salt plus concrete equals more porous concrete, a problem magnified by the fact that salts attract moisture. The best way to remove the chlorides and sulfates slowly corrupting the tunnel linings is a good old pressure washing.

Cracks and Delaminations: Sometimes the salts cause more damage than a pressure wash can handle. The Amtrak report identified a number of troubling cracks in the concrete, including several cracks more than an eighth of an inch wide—the threshold for being considered "severe." Engineers also found concrete "delamination," which basically means the solid layers have started to split and fray. These areas must be handled with additional care, filling the cracks and replacing the concrete as well as being washed.

A severe crack—more than 500 feet long and up to half an inch wide—lines an Amtrak tunnel beneath the East River. (Amtrak)

Bench Wall Replacement: The "most serious damage" to the Amtrak tunnels, according to the new engineering report, was that sustained by the concrete bench walls. These walls provide emergency access to (and exit from) trains, and their interiors house key electrical wiring, yet they suffered considerable cracks and corrosion. The new report suggests replacing the bench walls with new ones at a total cost of nearly $480 million, by far the highest-cost line item in the damage report.

Direct Fixation Tracks: And then there are the tracks themselves, which consist of rock ballast, timber ties, the main rail, and the electrified third rail. In the words of the engineering report, these components are "coated with chlorides" that can't be removed via washing. As with the bench walls, the only real option here is to replace the whole structure, though in this case the report recommends installing a new "direct fixation track system" in keeping with current best practices.

Amtrak officials told the New York Times and other media outlets last week that the long-term repairs require shutting down each of the tracks for at least a year. Until those fixes occur, the railroad might suffer more incidents like one outlined in the report from August 19, when a piece of bench wall from the Hudson River tunnel fell onto the tracks and led to train delays. The good news for taxpayers and travelers is that Amtrak believes the costs will be covered by insurance.

The bad news, of course, is that the repairs merely highlight the ongoing need for more tunnel capacity into and out of New York—the fulcrum of the popular Northeast Corridor, and the foundation of Amtrak's financial stability. Amtrak has a plan for that capacity in the form of its Gateway Tunnel beneath the Hudson. If the economic and transportation importance of rail in this part of the country isn't enough for federal officials to fund the Gateway, perhaps Sandy sympathy is.

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