New York has 26 subway lines, 490 stations and 660 miles of subway track.

CNN: New York subway system on alert

If subway rats have grown up eating from the trash bags and track litter of the subway system, those foods will prove most enticing.

WSJ: MTA Sets New Tactic in Rat War

Carrying nearly seven million passengers each day on nine lines and 327km of track, the Seoul subway has climate-controlled train cars with mobile phone reception, wireless internet and televisions.

BBC: Subway systems by the numbers

The machinery for track switches and motors on subway systems is often many decades old, and replacements aren't readily available when stores of backup parts have been used up as PATH's was after the storm.

WSJ: PATH's Road Back Is Rocky

One reason the PATH has been so much slower to recover than the New York City subway is the relatively greater expanse of track area that was subjected to coastal flooding in the storm, said Stephen Kingsberry, the acting director of the PATH, on a recent visit to Exchange Place in Jersey City.

WSJ: PATH's Road Back Is Rocky