NEW YORK – Every day, throngs of riders stand on the edge of danger in the nation's busiest subway system, waiting on platforms with nothing between them and the tracks.

Dozens of subway and light rail systems around the world have safety barriers with sliding doors on their platforms, but the idea hasn't gotten traction in New York. Yet transit officials are giving it a new look after two people were pushed and a third fell to their deaths on the tracks since early December.

Safety doors would be expensive and difficult additions to the sprawling, 108-year-old subway system, but some people are urging the Metropolitan Transportation Authority to try it. A company has proposed to install the barriers for free in exchange for advertising revenue.