Senators Susan Collins and Joseph Lieberman on Wednesday held a hearing to discuss lessons learned from the London attacks in July and what more should be done to secure the U.S. mass transit systems.

Testimony was provided by Polly Hanson, transit police chief at the Washington Metropolitan Area Transit Authority, and Michael Brown, chief operating officer of the London Underground.

Collins and Lieberman both pointed out that while many more Americans use public transit than airlines each day, only a fraction of what is being spent on aviation security is devoted to securing our mass transit systems.

"The attacks on London have been described as a wake-up call to those responsible for the safety and security of our own mass transit systems," Collins said. "And they are not the first. They echo the alarms set off by earlier attacks on mass transit in Madrid, Moscow, Tokyo, Tel Aviv and so many other cities around the world. Now that we have the alarm bell, it is time to act."

"Our government has a can-do, must-do attitude toward aviation security, but does not appear to have the same attitude toward transit security," Lieberman said. "This must change."