How safe are U.S. subways?

 system.

Najibullah Zazi, a former Denver airport shuttle driver, pleaded guilty last month to terrorism-related charges and admitted in court that he conspired with al Qaeda in Pakistan to blow up the New York subway system. Zazi planned to use a bomb made from the explosive triacetone triperoxide that he concocted from the chemicals in beauty supplies.

Last month, WPIX-TV in New York generated some headlines when its reporter found a police officer asleep in his security booth at the Grand Central terminal, one of the alleged targets of Zazi’s plot.

Others question the progress DHS has made in fortifying subways. The agency’s quaddrienniel security review released in February mentioned subways only once in more than 100 pages. “Subways have become a second child to some degree to the airlines,” said Scott Nelson, a former deputy assistant director of the FBI and former head of security for Warner Bros. Studios and Time Warner. Authorities rely more on police and intelligence to thwart subway attacks than technology and passenger screening, he added.

“Typically what drives improvements are problems,” said Nelson, now president of the corporate security firm Security & Risk Management Group, LLC. “But I think you will see in the future improved cameras, improved patrols with dogs. I think you will even see the possibility … of other screening like at airports. But I think it is still going to take a couple of serious events to get us completely there.”

Solomon writes that though long-held fears of a chemical and biological attack in a subway system arose in 1995 after the deadly sarin attack on the Tokyo subway, DHS began staging tests to study how such deadly chemicals might flow through the system last year. Washington was the first subway system tested and Boston, the nation’s oldest system, had its first tests back in December. Officials said devising long-term solutions are a long way off. DHS officials plan to study the results of the two tests to come up with early detection system recommendations.

The progress on studying and detecting chemical attacks on subway systems has been plodding. The U.S. Army as early as 1966 conducted a test simulating a biological attack on New York’s subway system, using a benign form of the Bacillus subtilis bacteria to show that trains rushing through tunnels would carry the germ throughout the entire subway system with ease, according to the book The Cult at the