New York City's subway system is the country's largest, with more than 460 stations, millions of daily riders and multiple entrances for each station. A decade after Sept. 11, city officials consider the mass transit system a top terror target.
The NYPD has a counterterror arsenal that includes more than 30 bomb-sniffing dogs, silent alarms, motion detectors and a vast security camera system.
Random bag checks are done tens of thousands of times each year. High-tech detection devices screen riders for peroxides or nitrates common in homemade explosives. And city police board subway cars and ask passengers to beware of suspicious packages.
Commuters say they're used to the "new normal". Mass transit is a huge terror concern in other countries, where subways have been bombed in Europe.