A huge emergency-response drill is to be held at the World Trade Center in New York on Sunday.
More than 800 police and firefighters will practice their response to a simulated explosion on a commuter train in a tunnel below the Hudson River that separates New York from New Jersey.
The drill is set to run from 6am - 11:30am (1000 - 1530 GMT) at the transit hub, which is surrounded by construction sites for skyscrapers and a memorial for victims of the September 11, 2001 attacks.
The World Trade Center site has been attacked twice, first by a truck bomb in 1993 and then in the September 11 attacks that destroyed the Twin Towers in 2001.
Since then, Madrid, London and Mumbai have been hit by attacks on their transit systems, putting New York on alert.
On 27 April, a plane used by President Barack Obama, escorted by a fighter jet, flew low over the Statue of Liberty near the World Trade Center site, creating a panic among New Yorkers who lived through September 11.
It turned out the flight had been staged for a photo shoot. The aide who authorized the flyover resigned on 8 May.