CHICAGO – The Chicago-area’s Metra commuter rail service is installing hundreds of portable, easy-to-use defibrillators on all of its trains, becoming only the second major transit system in the country to make the lifesaving machines available on trains, Metra officials said Thursday.

Defibrillators, devices that restore a normal heart rhythm with an electric shock, are required on airliners and in public places such as sports stadiums and large office buildings. But cost, lack of training and liability fears have prevented a greater proliferation of machines that advocates say are crucial to improving a dismal survival rate for people who suffer cardiac arrest.

“We’re adding something to our trains that hopefully none of us will have to use, but it’s like insurance: when we need it we want it,” Metra Chairman Brad O’Halloran said in announcing the initiative at a downtown Chicago Metra station.