In New Jersey and other parts of the eastern seaboard, evacuation orders have forced around a million people out of their homes. In New York City, the problem is somewhat different: Residents are largely stuck at home.

The country’s most extensive subway system has been put thoroughly out of commission by Hurricane Sandy. A 14-foot storm surge sent water into the tunnels and seems likely to have caused considerable damage.

“The subway system is 108-years-old. This is a system which was built over many years and was maintained very well, but salt water does not mix well with a subway system,” says Mitchell Moss, director of the Rudin Center for Transportation at NYU.

Moss says salt water can corrode eletrical parts and short-out the signaling system for trains.

City officials have not yet released a full damage assessment but have reported that all seven tunnels which carry trains under the East River are flooded. Moss says there may be significant repair costs to come, but in the immediate-term, the main cost will be loss of business activity due to the subway closure.