Vulnerable US mass transit systems leave Americans jittery

"Americans take public transportation 32 million times a day -- 16 times more often than they travel on domestic airlines -- and yet, when it comes to security, public transportation riders are treated as second-class citizens by the federal government," said American Public Transportation Association chief William Millar.

The US federal government has lavished about 18 billion dollars to make air travel safe, between the September 11, 2001 terror strikes and last May 31, compared to 250 million dollars for making public ground transportation safer, the AFTA says.

It believes the price of making necessary security upgrades at about six billion dollars. Many lawmakers, particularly among opposition Democrats, are pushing the cause.