And airlines are warning passengers that such disruption can be costly.

Although the driver managed to warn passengers of an imminent collision, 23 people were injured.

There is a small variable message sign on the platform that warns passengers about incoming trains.

The pilot reported smoke in the cabin, and warned passengers to adopt the "brace position".

However, as a frequent flier, I am tired of being ripped off and would like to warn other passengers.

They sound a whistle to warn waiting passengers of imminent arrivals.

Audio announcements also deliver station information and warns passengers of the train's movements.

Inside the airport, with its single ticket counter, a small sign warns passengers of random searches.

One recent morning, a conductor warned passengers that they'd better have their tickets out.

They warned passengers not to touch such containers and to report them immediately.